Psychiatric Comorbidity and Demographic Characteristics of 1,000 Children and Adolescents With ADHD in Turkey

Abstract

Objective: The objective was to examine the frequency of comorbid disorders in children and adolescents with ADHD in Turkey and to evaluate the distribution of comorbidities according to the subtypes of ADHD and sociodemographic features. Method: The sample consisted of 1,000 children, 6 to 18 years of age, including 242 females and 758 males, from Ege University who were diagnosed with ADHD. Results: The overall prevalence rate of psychiatric comorbidity in the study was 56.3%. The most frequently observed comorbidity was oppositional defiant disorder with a rate of 37.4%. Conduct disorder, depressive disorder, obsessive-compulsive disorder, and anxiety disorder accompanied ADHD, respectively. The results revealed that 70.2% of the children with ADHD-Combine type had at least one psychiatric comorbidity. Oppositional defiant disorder, conduct disorder, depressive disorder, and obsessive-compulsive disorder accompanied ADHD-Combine type in 54.6%, 12.6%, 8.1%, and 8.8% of the participants, respectively. Conclusion: These findings provide valuable information about the comorbid disorders in children and adolescents with a very large clinical sample of ADHD children.

Keywords

ADHD psychiatric comorbidity children adolescent

Introduction

ADHD is a neuropsychiatric disorder that is characterized by age-inappropriate inattention, hyperactivity, and impulsivity that emerge in childhood. It is the most common neurobehavioral disorder in primary school-aged children (Biederman & Faraone, 2005), and it negatively affects children’s normal development and academic and social functioning (Biederman et al., 2012; Spetie & Arnold, 2007). A comprehensive meta-analysis revealed that the global prevalence of ADHD is 5.29% (Polanczyk, Silva de Lima, Horta, Biederman, & Rohde, 2007). The clinical characteristics and epidemiology of ADHD differs between males and females (Nussbaum, 2012). ADHD is more common in males compared with females. The male to female ratio has been reported to vary from 3:1 to 10:1 in community samples (Biederman, 2005; Dalsgaard, Mortensen, Frydenberg, & Thomsen, 2002; Graetz, Sawyer, Hazell, Arney, & Baghurst, 2001). Three subtypes of ADHD are defined in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) based on nine inattention and nine hyperactivity-impulsivity criteria. The predominantly inattentive (PI) type is defined as six or more symptoms of inattention and fewer than six symptoms of hyperactivity/impulsivity. The predominantly hyperactive-impulsive type is defined as six or more symptoms of hyperactivity-impulsivity and fewer than six symptoms of inattention. Finally, the combined (CB) type is defined as six or more symptoms on both dimensions (Durak et al., 2014). Inattentive type is the most frequently seen subtype (Gadow et al., 2000; Gomez, Harvey, Quick, Scharer, & Harris, 1999). However, there are studies that have found a higher rate of the combined type (Graetz et al., 2001). In general, school problems, such as learning difficulties and failure in courses, are more common in the inattentive type, and behavioral problems are more common in the hyperactive-impulsive subtype; in the combined type, the symptoms are more severe. Previous studies have shown several comorbid psychiatric disorders in patients with ADHD (Kessler et al., 2006; Larson, Russ, Kahn, & Halfon, 2011). Most children diagnosed with ADHD are often found to have another comorbid psychiatric disorder besides ADHD. The presence of psychiatric comorbidities enhances the severity of the clinical picture and complicates the treatment procedures and process. Thus, there is great importance for an appropriate diagnosis and evaluation for psychiatric comorbidities. There are limited numbers of clinical-based studies that have been performed in Turkey on this issue. A clinical-based study conducted in Turkey by Hergüner and Hergüner (2012) revealed that 73.7% of the children with ADHD had at least one comorbid psychiatric disorder. There are many studies that have reported more than half of ADHD cases have at least one psychiatric comorbidity, and this rate increases with age (Gau et al., 2010; Jensen, Martin, & Cantwell, 1997; Yüce Zoroğlu, Ceylan, Kandemir, & Karabekiroğlu, 2013). Studies have shown that 54% to 84% of children and adolescents with ADHD may meet the criteria for oppositional defiant disorder (ODD); a significant portion of these patients will develop conduct disorder (CD; Ercan, Ardic, Kutlu, & Durak, 2012; Faraone, Biederman, Jetton, & Tsuang, 1997). ADHD and ODD are among the most common psychiatric disorders of childhood in either the community or clinical samples (Ghanizadeh, 2009; Willcutt et al., 2012). The rate of ADHD concurrent with ODD has been reported to vary between 40% and 95% (Steiner, 2007). CD is also one of the comorbidities of ADHD (Faraone et al., 1997; Kadesjö & Gillberg, 2001). Reports in the literature have documented a high psychiatric comorbidity in ADHD (Biederman et al., 1996; Faraone, Biederman, Mennin, Russell, & Tsuang, 1998), including ODD, CD (Drabick, Gadow, Carlson, & Bromet, 2004), mood disorders (Cohen et al., 1993; Eiraldi, Power, & Nezu, 1997), anxiety disorders (Gadow et al., 2000), learning disorder, tic disorder (Graetz et al., 2001), and substance use disorders (Burke, Loeber, & Lahey, 2001). The rate of mood and anxiety disorders concomitant with ADHD has been stated to be 20% to 40% (Biederman, Newcorn, & Sprich, 1991). Between 15% and 35% of children with ADHD or an anxiety disorder have both at the same time, such that ADHD is the most common externalizing comorbidity for anxiety (Levin-Decanini, Connolly, Simpson, Suarez, & Jacob, 2013). Family studies have stated that ADHD is widespread among children, adolescents, and adults with bipolar disorder (Faraone, Biederman & Monuteaux, 2001; Wilder-Willis et al., 2001). Tics are characterized by abnormal movements or vocalizations that are easily observed by others and might cause embarrassment or distress at school. Tic behaviors are relatively common in children, frequently associated with ADHD, and exhibited more often by males than females (Gadow, Nolan, Sverd, Sprafkin, & Schwartz, 2002). Comorbid tic disorder is known to have only a limited impact on the course, outcome, and treatment of ADHD (Spencer et al., 2001). Elimination disorders represent an inability to achieve or maintain control of bodily functions (Walsh & Menvielle, 2004). Nocturnal enuresis, which is common in children with ADHD, has been reported in 21% to 32% of children with ADHD (Bailey et al., 1999). Selective mutism (SM) is marked by a consistent failure to speak in certain social situations despite speaking and having knowledge of the spoken language in other situations, namely at home. SM is often comorbid with other psychiatric disorders, including other anxiety disorders and ADHD. Levin-Decanini et al. (2013) reported that children with SM have equal levels of social problems with ADHD children. In addition, a review of 33 identified studies showed evidence that the prevalence of symptoms of ADHD in children with autism spectrum disorder (ASD) was 33% to 37%. The clinical profile of ASD and ADHD is seen to be more severe than that of pure ADHD or ASD (Berenquer-Forner, Miranda-Casas, Pastor-Cerezuela, & Rosello-Miranda, 2015). ADHD and obsessive-compulsive disorder (OCD) are common developmental neuropsychiatric disorders associated with significant distress and dysfunction. The research on ADHD-OCD comorbidity faces empirical and conceptual difficulties that are likely interrelated. Empirically, reports of co-occurrence rates are highly inconsistent, ranging from 0% to 60% (Abramovitch, Goldzweig, & Schweiger, 2013), with much lower co-occurrence rates reported in adults relative to youth samples (Abramovitch, Dar, Mittelman, & Wilhelm, 2015). Heyman and colleagues (2001) reported that 40% of the 25 children ranging in age from 5 to 15, diagnosed with OCD, had an additional comorbid psychiatric condition, but none was diagnosed with ADHD. Similarly, Toro, Cervera, Osejo, and Salamero (1992) stated that of 72 children with OCD recruited from hospitals and private clinics, only 5.5% had a concomitant diagnosis of ADHD. By contrast, Geller et al. (2000) reported that 59% of the children diagnosed with OCD in the general psychopharmacology clinic and 44% of the children in the OCD specialized clinic had a concomitant diagnosis of ADHD. Whereas the above studies stated the occurrence of ADHD in children diagnosed with OCD, only a few studies have documented the occurrence of OCD in children and adolescents diagnosed with ADHD. Increased co-occurrence rates were found in children and adolescents compared with adults (Abramovitch et al., 2015). A limited number of studies reported the breakdown of ADHD subtypes in individuals with ADHD-OCD comorbidity. Geller et al. (2002) reported 69% of ADHD-combined type and 24% of ADHD-inattentive type in a sample of youth with comorbid OCD and ADHD, which is consistent with Willcutt’s meta-analysis (Willcutt, 2012). In contrast with these studies, Anholt and colleagues (2010) reported that 48% of ADHD-inattentive type and 36% of ADHD-combined type were present in a sample of adults with comorbid ADHD-OCD.

The rate of comorbid diagnoses may vary according to ADHD subtypes, age, and sex. Connor et al. (2003) reported that ODD and CD have been seen in early childhood in ADHD; however, mood and anxiety disorders appear in older ages. Lahey et al. (1998) stated anxiety disorder has been seen more in ADHD-inattentive type than ADHD-combined type. Hinshaw (2002) stated that ODD was more common in ADHD-combined type. Yüce et al. (2013) found that the comorbidity of depression and anxiety disorder with ADHD were more common in girls than boys.

The objective of this study was to examine the frequency of comorbid disorders in children and adolescents with ADHD in Turkey and to evaluate the distribution of comorbidities according to the subtypes of ADHD and sociodemographic features.

Method

Sampling Process

This study was a cross-sectional study. The sample consisted of 1,000 children, 6 to 18 years of age (10.82 ± 3.24), including 242 females and 758 males, from Ege University who were diagnosed with ADHD according to the DSM-IV criteria. The assessment was conducted in the first psychiatric admission using the Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children–Present and Lifetime version (K-SADS-PL) to parents.

Mental retardation, having a history of head injury with a loss of consciousness, and having a neurological disease or other serious medical diseases were exclusion criteria for participants.

Assessment Procedures

Our recruitment and screening procedures were designed to collect data from a carefully diagnosed sample of children and adolescents for ADHD comorbidities and subtypes. The children and adolescents were first interviewed using the K-SADS-PL (Gökler et al., 2004). The K-SADS-PL is a semi-structured diagnostic interview schedule based on the DSM-IV criteria, which investigates a wide range of psychiatric disorders. Families and teachers completed the Turgay DSM-IV Disruptive Behavior Disorders Rating Scale–teacher and parent forms (T-DSM-IV-S). The T-DSM-IV-S was developed by Turgay (1994) and translated and adapted by Ercan, Amado, Somer, and Çıkoğlu (2001). T-DSM-IV-S is based on the DSM-IV diagnostic criteria and assesses hyperactivity-impulsivity, inattention, opposition defiance, and CD.

During the psychiatric assessment of the diagnosis, participants were required to exhibit at least six of the nine symptoms of attention deficit or hyperactivity and to have reported at least six attention deficit or hyperactivity symptoms during childhood for the ADHD diagnosis to be upheld. The returned parent and teacher version of the T-DSM-IV-S forms were scored, and the children and adolescents who scored less than one standard deviation below the relevant age norms on the ADHD subscales were excluded from the study.

A “best estimate procedure” was used to determine the final diagnoses. The “best estimate procedure” is defined here as determining the diagnostic status after reviewing all teacher and parent scales and the K-SADS-PL.

Data Analysis

Statistical analyses were performed using SPSS 18. Descriptive statistics are expressed as the mean, standard deviation, and percentage. All continuous variables were tested for normality and homogeneity of variance. The continuous variables were not normally distributed; therefore, the Mann–Whitney U test and Pearson’s chi-square analysis were performed; p values less than .05 were accepted to be statistically significant.

Results

The mean age of all participants was 10.82 ± 3.24 years; 608 children were in the 6 to 11 years age group, and 392 children were in the 12 to 18 years age group. The most frequent type in our sample was the ADHD-combined type. Among these children, 57.1% were diagnosed with ADHD-combined type (ADHD-C), 39.9% were ADHD-inattentive type (ADHD-I), and 3% were ADHD-hyperactive-impulsive type (ADHD-H). The sociodemographic features according to ADHD subtypes are presented in Table 1.

Table 1.

Sociodemographic Features According to ADHD Subtypes.

	ADHD-C		ADHD-I		ADHD-H		χ²	p
	n	%	n	%	n	%	χ²	p
Gender
Male	473	82.8	240	65.2	25	3.3	40.95	<.00*
Female	98	17.2	139	34.8	5	16.7	40.95	<.00*
Age groups
6-11 years (child)	389	64	194	31.9	25	4.1	44.07	<.05*
12-18 years (adolescent)	182	46.4	205	52.3	5	1.3	44.07	<.05*

Note. ADHD-C = ADHD-combined type; ADHD-I = ADHD-inattentive type; ADHD-H = ADHD-hyperactive/impulsive type.

p < .05.

The analysis of the data revealed that the prevalence of ADHD was significantly higher in males than in females. ADHD-inattentive type (54.7%) was more common in females, and ADHD-combined type (62.4%) was more often seen in males. ADHD-C (40.5%) and then ADHD-H (2.1%) were seen in females after ADHD-I. As for males, ADHD-C was followed by ADHD-I (34.3%) and ADHD-H (3.3%). There were significant differences between gender according to ADHD subtypes (p < .05).

The overall prevalence rate of psychiatric comorbidity was 56.3% (N = 1,000; 95% CI = [53.2, 59.3]). The most frequently observed comorbidity was ODD with a rate of 37.4%. CD, depressive disorder, OCD, and anxiety disorder accompanied ADHD in 7.6%, 7.2%, 7.1%, and 5.6% of the participants, respectively. The psychiatric comorbidities are presented in Figure 1.

Figure 1.

Distribution of psychiatric comorbidities in children with ADHD.

When the psychiatric comorbidities were assessed, 41.3% of the children with ADHD had one, 12% had two, and 3% had three or more psychiatric comorbidities. There were significant differences among the ADHD subtypes according to having a psychiatric comorbidity, χ²(1, 6) = 130.46, p < .05. There were no statistically significant differences among subtypes according to gender or age (p > .05). At least one comorbid disorder was present in 42.4% of children aged between 6 and 12 years and 39.5% of adolescents aged between 12 and 18 years. Among the children and adolescents who had at least one psychiatric comorbidity, the combined type of ADHD was present in 401 (70.2%), the inattentive type was present in 146 (36.6%), and the hyperactive/impulsive type was present in 16 (53.3%). The number of psychiatric comorbidities according to ADHD subtypes are presented in Table 2.

Table 2.

The Distribution of the Number of Psychiatric Comorbidity in ADHD Subtypes.

	None		One comorbidity		Two comorbidity		Three and more comorbidity
	N	%	n	%	n	%	n	%
ADHD-I	253	63.4	130	32.6	11	2.8	5	1.3
ADHD-C	170	29.8	273	47.8	103	18	25	4.4
ADHD-H	14	46.7	10	33.3	6	20	—

Note. ADHD-C = ADHD-combined type = ADHD-I: ADHD-inattentive type = ADHD-H: ADHD-hyperactive/impulsive type.

ODD and CD were frequently seen with ADHD-combined type, whereas anxiety disorder was seen more frequently in children diagnosed with ADHD-inattentive type. After the pairwise comparisons, ODD was more common in children who were diagnosed with the ADHD-combined type than the other two ADHD types (p < .05). CD was seen in children with ADHD-C and ADHD-I (p < .05). Although it was almost significant, OCD was consistently present in children with ADHD-C and ADHD-I (p > .05). In our sample, depressive disorder was seen equally in children who were diagnosed with ADHD-C and ADHD-I. Psychiatric comorbidities according to ADHD subtypes are presented in Table 3.

Table 3.

Psychiatric Comorbidities According to ADHD Subtypes.

	ADHD-C		ADHD-I		ADHD-H		χ²	p
	n	%	n	%	n	%	χ²	p
Oppositional defiant disorder	312	54.6	48	12	14	3.7	183.28	<.05*
Conduct disorder	72	12.6	1	0.3	3	10	51.34	<.05*
Depressive disorder	46	8.1	25	6.3	1	3.3	1.81	>.05
Obsessive-compulsive disorder	50	8.8	20	5	1	0.1	5.65	<.05*
Anxiety disorder	8	1.4	48	12	—		52,03	0.00*
Tourette’s disorder	16	2.8	8	2	—		1.39	>.05
Asperger syndrome	34	6	3	0.8	2	6.7	17,59	0.00*
Enuresis	8	1.4	1	0.3	1	3.3	4.84	>.05
Encopresis	2	0.4	—		—		1.50	>.05
Dyslexia	—		2	0.5	—		3.01	>.05
Bipolar disorder	5	0.9	4	1	—		0.32	>.05
Substance abuse	3	0.3	—		—			>.05
SM	—		1	0.3	—		1.50	>.05

Note. ADHD-C = ADHD-combined type; ADHD-I = ADHD-inattentive type; ADHD-H = ADHD-hyperactive/impulsive type; SM = selective mutism.

p < .05.

With regard to gender, ODD and CD were more common in male cases (p < .05). Depressive disorder, OCD, anxiety disorder, and bipolar disorder were more frequent in female cases (p < .05; Table 4).

Table 4.

Psychiatric Comorbidities With ADHD Children According to Gender.

	Female		Male		χ²	p
	n	%	n	%	χ²	p
Oppositional defiant disorder	59	24.4	311	41.6	23.11	0.00*
Conduct disorder	12	5	64	8.4	3.17	>.05
Depressive disorder	25	10.3	47	6.2	4.68	<.05*
Obsessive-compulsive disorder	25	10.3	46	6.1	5.05	<.05*
Anxiety disorder	37	15.3	19	2.5	56.69	0.00*
Tourette’s disorder	2	0.8	22	2.9	3.37	>.05
Asperger syndrome	5	2.1	34	4.5	2.86	>.05
Enuresis	1	0.4	9	1.2	1.11	>.05
Encopresis	—		2	0.3	0.64	>.05
Dyslexia	1	0.4	1	0.1	0.72	>.05
Bipolar disorder	8	3.3	1	0.1	20.71	<.05*
Substance abuse	—		3	0.4	0.96	>.05
SM	—		1	0.1	0.32	>.05

Note. SM = selective mutism.

p < .05.

With regard to age group, the rate of ODD appears in early childhood in ADHD. Moreover, no significant difference was found between early childhood and adolescent cases according to CD comorbidity. Anxiety disorder and depressive disorder were more common at older ages. The rate of substance abuse and bipolar disorders were also significantly higher in adolescent cases compared with early childhood cases. OCD was more common in adolescents (n = 34), but no significant difference was found. There were no significant differences between age groups in terms of the rate of enuresis, encopresis, dyslexia, SM, and Tourette’s disorder comorbidities (p > .05). The psychiatric comorbidities with ADHD children according to age groups are presented in Table 5.

Table 5.

Psychiatric Comorbidities With ADHD Children According to Age Group.

	Child (6-11 years)		Adolescent (12-18 years)		χ²	p
	n	%	n	%	χ²	p
Oppositional defiant disorder	248	40.8	126	32.1	7.61	<.05*
Conduct disorder	45	7.4	31	7.9	0.08	>.05
Depressive disorder	33	5.4	39	9.9	7.29	<.05*
Obsessive-compulsive disorder	37	6.1	34	8.7	2.42	>.05
Anxiety disorder	17	2.8	39	9.9	23.06	<.05*
Tourette’s disorder	11	1.8	13	3.3	2.31	>.05
Asperger syndrome	39	6.4	—		26.16	<.05*
Enuresis	8	1.3	2	0.5	1.56	>.05
Encopresis	1	0.2	1	0.3	0.09	>.05
Dyslexia	2	0.3	—		1.29	>.05
Bipolar disorder	2	0.3	7	1.8	5.67	<.05*
Substance abuse	—		3	0.8	4.66	<.05*
SM	—		1	0.3	1.55	>.05

Note. SM = selective mutism.

p < .05.

Discussion

The aim of the present study was to examine the frequency of comorbid disorders in children and adolescents with ADHD in Turkey and to evaluate the distribution of comorbidities according to the ADHD subtypes and age group features. As expected, ADHD cases in our study often had a number of other psychiatric disorders besides ADHD (56.3%; Barkley, 2006). It is well known that comorbidity is a rule and not an exception in ADHD, and at least more than 50% of patients with ADHD have psychiatric comorbid disorders, which is in line with our findings (Pliszka, 2003; Wilens et al., 2002). However, most of the studies from other countries and from Turkey, including the Multimodal Treatment Study of Children With ADHD (MTA) study, report much higher comorbidity rates than our rate of 56.3% in clinical samples of ADHD (Jensen et al., 2001; Kessler et al., 2006). In an MTA, which involved 579 young children with combined-type ADHD, 70% of the children fully met the diagnostic criteria for at least one other psychiatric disorder (MTA Cooperative Group, 1999). Similar to the MTA study, we found that 70.2% of the children with ADHD-C had at least one psychiatric comorbidity. The lower rates of ADHD-I may be explained by a random selection of the cases. Moreover, in the present study, ADHD-C children (70.2%) had more psychiatric comorbidities compared with children with ADHD-I (36.6%). Barkley (2006) indicated that psychiatric comorbidity was largely confined to the combined type of ADHD. The psychiatric comorbidity rates of ADHD were lower in our study than other studies, but this may be explained by the cases of ADHD-C selected in other studies, notably the MTA study. The low rate of comorbidity, which was approximately 50% in our overall sample, was due to the low comorbidity rates of psychiatric disorders in children with ADHD-I. Consistent with these previous studies, when only ADHD-C was analyzed in our sample, about 70% of children had psychiatric comorbidities. Unlike the findings reported by Barkley (2006), we assessed the differences between ADHD subtypes in regard to the existence of psychiatric comorbidity.

Among the 1,000 ADHD children examined in the present study, 413 (41.3%) had one psychiatric comorbidity, 120 (12%) had two, and 30 (3%) had at least three. Consistent with the present study, Barkley (2006) stated that up to 44% of ADHD children have at least one other psychiatric disorder and 43% have at least two or more additional psychiatric disorders. The results of the present study are also in accordance with reports in the literature. Biederman et al. (1991) reported two or more comorbidities in 20% of ADHD cases in a clinical sample.

In the present study, 57.1% of the children were diagnosed with ADHD-C, 39.9% with ADHD-I, and 3% with ADHD-H. A meta-analysis by Willcutt et al. (2012) revealed that ADHD-I was the most frequently observed type in the population; however, ADHD-C was probably referred to the clinical-based study. Byun et al. (2006) stated that the prevalence of ADHD-C was 66.7%, ADHD-I was 21%, and ADHD-H was 1% in a clinical-based study. Similarly, Huh et al. (2011) found that ADHD-C was more frequent than other subtypes. In our study, we found the rate of the combined type was higher than that for the other types. This is also consistent with the results of other studies (Huh et al., 2011; Polanczyk et al., 2007). There might be a transition between ADHD subtypes with age. The high rates of ADHD-C in our study were typically because of the mean age of our sample (10.82 ± 3.24). It is known that the transition could be from ADHD-C to ADHD-I in later years (Ercan et al., 2013).

The difference between the male and female prevalence of ADHD is a well-known fact, and community-based studies have reported that ADHD affects male more commonly than females (Skounti, Philalithis, & Galanaki, 2007). These results are consistent with those of previous studies demonstrating a gender difference (Bradshaw & Kamal, 2014; Faraone, Sergeant, Gillberg, & Biederman, 2003; Polanczyk et al., 2007). In our study, and similar to Polanczyk and Jensen (2008), ADHD was more common in males. Based on these findings, it would be justifiable to presume that ADHD-related symptoms and comorbidities present in males are more easily noticed by parents and are, therefore, more often referred to the clinic (Joelsson et al., 2015). Moreover, within clinic-referred samples, the sex ratio can be considerably higher, suggesting that boys with ADHD are far more likely to be referred to clinics than girls. This is probably because boys are more likely to have a comorbid oppositional or CD. In our study, when investigating the frequency of ADHD subtypes relative to gender, ADHD-I was more common in females, and ADHD-C was more common in males (Willcutt et al., 2012).

In our study, ODD was significantly more common in children with ADHD, with a rate of 37.4%. Similar to the present study, other studies have stated that the highest comorbidity rates reported among children and adolescents with ADHD are for ODD, and the rate of comorbid ADHD and ODD has been estimated at approximately 39% to 59% (Biederman et al., 2007; Byun et al., 2006; Ghanizadeh, 2009). Some studies have assessed ADHD as a risk factor for development of ODD and CD (Connor, 2015; Taurines et al., 2010). Moreover, ODD was encountered more frequently in ADHD-C (54.6%). This finding is consistent with many other studies in the literature, which also report that ODD was seen more often in the ADHD-C type (Hinshaw, 2002; Huh et al., 2011; Wyman et al., 2009). Erşan, Doğan, Doğan and Sümer (2004) reported that the highest rate of association with ODD was with ADHD-C subtype (65.6%); the lowest was with ADHD-I subtype (43.2%).

High comorbid rates of ADHD and CD in children have been reported in previous studies (Biederman et al., 1996). In an epidemiological study, August, Realmuto, Macdonal, Nugent, and Crosby (1996) reported that the rate of CD is 12%. Consistent with previous studies, we found the rate of CD in children with ADHD was 7.6%. In addition, Gau et al. (2010) indicated that a childhood diagnosis of ADHD predicts a higher risk for ODD/CD in adolescence. In contrast with these findings, this study shows that there was no significant difference between age groups based on participation in a treatment process. Our findings suggest that CD was more common in the ADHD-C type. This could be interpreted as behavioral problems were more often seen in ADHD-C subtype because of the symptom severity and having greater difficulty in regulating emotions. Faraone and colleagues (1995) indicated that children with ADHD-C, particularly those with severe and persistent ADHD symptoms, are at increased risk for the development of conduct problems, including ODD and CD. Ercan et al. (2013) indicated that CD was more frequent in males than females, which is line with our findings. Although, Disney, Elkins, McGue, and Lacono (1999) stated that there were no differences between genders.

Anxiety disorders occur in up to one third of patients with ADHD (Biederman et al., 1991; Manassis, Tannock, & Barbosa, 2000; MTA Cooperative Group, 1999; Pliszka, 2003). Inconsistent with our findings was the finding that anxiety and ADHD had a comorbidity rate that was 5.6%. Thus, the rate of comorbid anxiety disorders and ADHD seems to vary from 10% to 40% in clinic-referred children (Barkley, 2006; Manassis et al., 2000). The rate of OCD and ADHD comorbidity has been estimated at 13.6% (APA, 2000). In addition, in the present study, the comorbidity rate for OCD in an ADHD sample was 7.1%. In the MTA study, only 4% of the children met the criteria for mood disorder (Jensen et al., 2001). The findings about the rate of depression (7.2%) are slightly congruent with the MTA study. This lower prevalence of depression, anxiety disorder, and OCD may be explained by the current sample being older. According to the sample size, the distribution range is expanding. Consistent with previous studies (Biederman et al., 2004; Gau et al., 2010; Levy, Hay, Bennett, & McStephen, 2005), depression, anxiety disorder, and OCD were more common in females. In the present study, with regard to age groups, the rate of depression and anxiety disorder was significantly higher in adolescents compared with the children. Consistent with the present findings, anxiety disorder and depression were seen in adolescents (Biederman et al., 2004; Small et al., 2008). While studies have demonstrated that OCD is more common in childhood (Spencer, Biederman, & Wilens, 1999), our findings indicate that there is no significant difference in OCD according to age group, which is consistent with the findings of Weidle, Jozefiak, Ivarsson, and Thomsen (2014). With respect to the ADHD subtypes, the frequency of anxiety disorder was higher in ADHD-I, whereas the frequency of OCD was higher in ADHD-C. Depressive disorder was not significantly different among the ADHD subtypes. One persisting clinical belief is that anxiety disorders are more likely to co-occur with the DSM-IV ADHD-I than with other subtypes (APA, 2000). Many studies state that children with ADHD-C and ADHD-I show similar levels of anxiety and depression (Byun et al., 2006; Power, Costigan, Eiraldi, & Leff., 2004).

In addition, ADHD was accompanied by bipolar disorder in nine children. One study by Carlson (2005) that involved 326 cases with ADHD demonstrated that 18 of the children with ADHD met the criteria for bipolar disorder. Our findings are in agreement with the previous study. We found that bipolar disorder was seen more in females with ADHD in adolescents. Faraone et al. (1998) stated that the rate of bipolar disorder was 22% in children and 28% in adolescents with ADHD. In contrast with our findings, most studies revealed that bipolar disorder in children with ADHD occurred predominately in males (Biederman et al., 1996; Geller et al., 2000). There were no significant differences among ADHD subtypes. It is difficult to generalize these findings due to the limited number of cases of diagnosed bipolar disorder.

In our sample, 2.4% of the children had tic disorder. However, there was no significant difference with regard to age, gender, or ADHD subtypes. Consistent with our study, Gau et al. (2010) indicated that the rate of tic disorder in ADHD was lower than what many previous studies reported and ranged from 10.9% to 33% (Kadesjö & Gillberg, 2001; MTA study, 1999).

However, previous studies have demonstrated a significantly increased prevalence of ADHD in children with enuresis (Baeyens Roeyers, & Walle, 2006; Liu, Sun, Uchiyama, Li, & Okawa, 2000). The rate of comorbid ADHD and enuresis was 10.3% (Baeyens et al., 2006). According to our findings, ADHD was accompanied by enuresis and encopresis in 1% and 0.25%, respectively.

A childhood diagnosis of ADHD may increase the risk for substance use (APA, 2000; Gaus et al., 2010). August et al. (2006) found that drug abuse was most common in adolescents. Consistent with the results of the study by August et al. (2006), we found that substance abuse was seen more in males with ADHD and in adolescents. All three adolescents were diagnosed with ADHD-C. In contrast to our study, Turgay (2005) reported no significant differences among the ADHD subtypes according to substance use in adolescents.

Learning disorders are known to frequently accompany ADHD, and the risk is especially higher in ADHD-I (Gillberg, 2004). In present study, the rate of learning disorder in ADHD was lower than what was reported in many previous studies (Baeyens et al., 2006; Gillberg, 2004). The lower rates of learning disorders may be explained by the random selection of cases and the high socio-economic levels of families.

In the clinical population, the rate of SM was lower than 1% (APA, 2000). Consistent with the literature, we found that the rate of SM in children with ADHD was 0.1%.

The rate of Asperger disorder in children with ADHD was 3.9%. All of them were diagnosed with ADHD-C type. With regard to age group, Asperger disorder was seen more in childhood. Consistent with the recent study, Mukaddes, Hergüner, and Tanidir (2010) stated that Asperger disorder was most common with ADHD and more seen in ADHD-C type.

In conclusion, the present study found a high rate of comorbidity (56.3%) in children and adolescents with ADHD. The most common comorbidities were ODD, CD, depressive disorder, OCD, and anxiety disorder. There were two different views about the etiology of the comorbidity among depression and ADHD. It has been suggested that depressive symptoms among children with ADHD may reflect the demoralizing effects of ADHD across domains of functioning (Waxmonsky, 2003). However, Biederman et al. (2006) found that the course of depressive symptoms was independent of ADHD, suggesting that the mood symptoms reflected a separate diagnostic entity. In the general consensus that both genetic and non-genetic factors play an etiological role in both ADHD, anxiety and depression have motivated several approaches to provide insights into underlying mechanisms for the comorbidity between ADHD, anxiety, and depression (Brown, 2009). Tic disorder, enuresis, encopresis, SM, substance abuse, dyslexia, bipolar disorder, and Asperger syndrome also accompanied ADHD. ODD and CD were more frequent in males, whereas depressive disorder, OCD, and anxiety disorder were more common in females. ODD was more common in children, whereas anxiety disorder, depression, and OCD were more common in adolescents. In general, when we assessed the rates of comorbidities in different age groups, the rate of depression and anxiety tend to be higher with increasing age. However, Asperger disorder and ODD were more common in childhood in our study. ADHD symptoms (along with any concurrent symptoms of ODD, CD) are typically the major concerns of the parents and teachers during the childhood (Barkley, 2006). On the contrary, poor achievement in school, problems with parents and teachers, and low self-esteem tend to be major concerns in adolescence, and internalizing problems (e.g., anxiety, sadness) and concerns about underachievement predominate in adulthood (Barkley, 2006; Biederman et al., 2006). In addition, except for anxiety disorder, depression, OCD, ODD, and CD were more frequent in ADHD-C in this study. Consistent with the recent study, one persisting clinical belief is that anxiety disorders are more likely to co-occur with ADHD-inattentive subtype than with others (Brown, 2009).

Limitations and Strengths

Several weaknesses need to be considered when interpreting our present findings. The limitations of this study are that it only included children and adolescents from the Department of Psychiatry in Ege University. Therefore, we should consider that these results may not reflect the general population of children and adolescents. The other limitation is the high socio-economic level of our sample.

Conclusion

Despite the several limitations of this study, these findings provide valuable information about the comorbid disorders in children and adolescents with a very large clinical sample of ADHD children with a mid-to-high socio-economic status (SES) in Turkey. The assessment of the relationship between ADHD subtypes and psychiatric comorbidities in the sample was noteworthy. Most studies have assessed the relationship between the existence of ADHD and comorbidities, and the result from this study is a useful addition to the other studies focusing on the relationships between ADHD and comorbidities.

The present results highlight the need for more research in this area, as well as the importance of screening comorbidities among children and adolescents diagnosed with ADHD.

Footnotes

Acknowledgements

We thank Dr. Fatma Sibel Durak for help with the statistical analyses.

Authors’ Contributions

Study concept and design: Eyüp Sabri Ercan, Sevim Berrin İnci, Melis İpci. Acquisition of data: Sevim Berrin İnci, Melis İpci. Analysis and interpretation of data: Eyüp Sabri Ercan, Sevim Berrin İnci, Melis İpci. Drafting of article: Sevim Berrin İnci, Melis İpci. Critical revision: Eyüp Sabri Ercan

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Dr. Ercan is on advisory boards for Eli Lilly Turkey and Janssen Turkey.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Author Biographies

Sevim Berrin Inci is a Senior Psychologist and Cognitive Behavioral Psychotherapist and is working on children and adolescents with ADHD. Up to date had several publications about ADHD.

Melis Ipci is a Psychologist and is working on ADHD children and adolescents. Up to date had several publications about ADHD.

Ulkü Akyol Ardıç worked as a research assistant in Ege University Faculty of medicine Department of Child and Adolesecent psychiatry. ADHD and ADHD like symptoms in Autism are among her areas of interest.

Eyup Sabri Ercan is a Professor in the Department of Child and Adolescent psychiatry in the School of Medicine at Ege University, turkey. He also obtained his MD and training in child and adolescent psychiatry at Ege University. He passed the United Stated Medical Licensing Examination (USMLE) basic and clinical science exams in 1995. He worked as an observer doctor at scarborough General Hospital ADHD clinic in 1997. His clinical and research interest over his 20 year career have focused on ADHD and pediatric psychopharmacology. He is the director of ADHD commission of Turkish Child and Psychiatric Association. Also, he is a councillor of World Psychiatry Association of Child and Adolescent Psychiatry.

References

Abramovitch

Dar

Mittelman

Wilhelm

(2015). Comorbidity between attention deficit/hyperactivity disorder and obsessive-compulsive disorder across the lifespan: A systematic and critical review. Harvard Review of Psychiatry, 23, 245-262.

Abramovitch

Goldzweig

Schweiger

(2013). Correlates of physical activity with intrusive thoughts, worry and impulsivity in adults with attention deficit/hyperactivity disorder: A cross-sectional pilot study. The Israel Journal of Psychiatry and Related Sciences, 50(1), 47-54.

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author.

American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (4th ed., text rev.). Washington, DC: Author.

Anholt

G. E.

Cath

D. C.

van Oppen

Eikelenboom

Smit

J. H.

van Megen

Van Balkom

A. J.

(2010). Autism and ADHD symptoms in patients with OCD: Are they associated with specific OC symptom dimensions or OC symptom severity? Journal of Autism and Developmental Disorders, 40, 580-589.

August

G. J.

Realmuto

G. M.

Macdonal

A. W.

Nugent

S. M.

Crosby

(1996). Prevalence of ADHD and comorbid disorders among elementary school children screened for disruptive behavior. Journal of Abnormal Child Psychology, 24, 571-595.

August

G. J.

Winters

K. C.

Realmuto

G. M.

Fahnhorst

Botzet

M. A.

Lee

(2006). Prospective study of adolescent drug use among community samples of ADHD and Non-ADHD participants. Child & Adolescent Psychiatry, 45, 824-832.

Baeyens

Roeyers

Walle

J. V.

(2006). Subtypes of attention-deficit/hyperactivity disorder (ADHD): Distinct or related disorders across measurement levels? Child Psychiatry and Human Development, 36, 403-417.

Bailey

Ornitz

E. M. N.

Gehricke

J. G.

Gabikian

Russell

A. T.

Smalley

S. L.

(1999). Transmission of primary nocturnal enuresis and attention deficit hyperactivity disorder. Acta Paediatrica, 88, 1364-1368.

10.

Barkley

R. A.

(2006). The relevance of the still lectures to attention-deficit/hyperactivity disorder: A commentary. Journal of Attention Disorders, 10, 137-140.

11.

Berenquer-Forner

Miranda-Casas

Pastor-Cerezuela

Rosello-Miranda

(2015). Comorbidity of autism spectrum disorder and attention deficit hyperactivity. A review study. Revista de Neurologia, 60, 37-43.

12.

Biederman

(2005). Attention-deficit/hyperactivity disorder: A selective overview. Biological Psychiatry, 57, 1215-1220.

13.

Biederman

Faraone

S. V.

(2005). Attention deficit hyperactivity disorder. Lancet, 366, 237-248.

14.

Biederman

Faraone

S. V.

Milberger

Curtis

Chen

Marrs

… Spencer

(1996). Predictors of persistence and remission of ADHD into adolescence: Results from a four-year prospective follow-up study. Journal of the American Academy of Child & Adolescent Psychiatry, 35, 343-351.

15.

Biederman

Fried

Petty

Mahoney

Faraone

S. V.

(2012). An examination of the impact of attention-deficit hyperactivity disorder on IQ: A large controlled family-based analysis. Canadian Journal of Psychiatry/Revue canadienne de psychiatrie, 57, 608-616.

16.

Biederman

Monuteaux

M. C.

Faraone

S. V.

Hirshfeld-Becker

D. R.

Henin

Gilbert

Rosenbaum

J. F.

(2004). Does referral bias impact findings in high-risk offspring for anxiety disorders? A controlled study of high-risk children of non-referred parents with panic disorder/agoraphobia and major depression. Journal of Affective Disorder, 82, 209-216.

17.

Biederman

Monuteaux

M. C.

Mick

Spencer

Wilens

T. E.

Klein

K. L.

… Faraone

S. V.

(2006). Psychopathology in females with attention-deficit/hyperactivity disorder: A controlled, five-year prospective study. Biological Psychology, 60, 1098-1105.

18.

Biederman

Newcorn

Sprich

(1991). Comorbidity of attention deficit hyperactivity disorder with conduct, depressive, anxiety, and other disorders. The American Journal of Psychiatry, 148, 564-577.

19.

Biederman

Spencer

T. J.

Newcorn

J. H.

Gao

Milton

D. R.

Feldman

P. D.

Witte

M. M.

(2007). Effect of comorbid symptoms of oppositional defiant disorder on responses to atomoxetine in children with ADHD: A meta-analysis of controlled clinical trial data. Psychopharmacology, 190, 31-41.

20.

Bradshaw

L. G.

Kamal

(2014). Prevalence of ADHD in Qatari School-Age Children. Journal of Attention Disorders. Advance online publication. doi:10.1177/1087054713517545

21.

Brown

T. E.

(2009). ADHD comorbidities: Handbook for ADHD complications in children and adults. Arlington, TX: American Psychiatric Publishing.

22.

Burke

J. D.

Loeber

Lahey

B. B.

(2001). Which aspects of ADHD are associated with tobacco use in early adolescence. Journal of Child Psychology and Psychiatry, 42, 493-502.

23.

Byun

Yang

Lee

Jang

Yang

J. W.

Kim

J. H.

… Joung

Y. S.

(2006). Psychiatric comorbidity in Korean children and adolescents with attention-deficit hyperactivity disorder: Psychopathology according to subtype. Yonsei Medical Journal, 47, 113-121.

24.

Carlson

G. A.

(2005). Early onset bipolar disorder: Clinical and research considerations. Journal of Clinical Child & Adolescent Psychiatry, 34, 333-343.

25.

Cohen

Kasen

Velez

C. N.

Hartmark

Johnson

… Streuning

E. L.

(1993). An epidemiological study of disorders in late childhood and adolescence–I. Age- and gender-specific prevalence. Journal of Child Psychology and Psychiatry, 34, 851-867.

26.

Connor

D. F.

(2015). Pharmacological management of pediatric patients with comorbid attention-deficit hyperactivity disorder oppositional defiant disorder. Pediatric Drugs, 17, 361-371.

27.

Connor

D. F.

Edwards

Fletcher

K. E.

Baird

Barkley

R. A.

Steingard

R. J.

(2003). Correlates of comorbid psychopathology in children with ADHD. Journal of the American Academy of Child & Adolescent Psychiatry, 42, 193-200.

28.

Dalsgaard

Mortensen

P. B.

Frydenberg

Thomsen

P. H.

(2002). Conduct problems, gender and adult psychiatric outcome of children with attention- deficit hyperactivity disorder. The British Journal of Psychiatry, 181, 416-421.

29.

Disney

E. R.

Elkins

I. J.

McGue

Lacono

W. G.

(1999). Effects of ADHD, conduct disorder, and gender on substance use and abuse in adolescence. The American Journal of Psychiatry, 156, 1515-1521.

30.

Drabick

D. A.

Gadow

K. D.

Carlson

G. A.

Bromet

E. J.

(2004). ODD and ADHD symptoms in Ukrainian children: External validators and comorbidity. Journal of the American Academy of Child & Adolescent Psychiatry, 43, 735-743.

31.

Durak

Ercan

E. S.

Ardic

U. A.

Yuce

Ercan

Ipci

(2014). Effect of methylphenidate on neurocognitive test battery: An evaluation according to the diagnostic and statistical manual of mental disorders, fourth edition, subtypes. Journal of Clinical Psychopharmacology, 34, 467-474.

32.

Eiraldi

R. B.

Power

T. J.

Nezu

C. M.

(1997). Patterns of comorbidity associated with subtypes of attention-deficit/hyperactivity disorder among 6- to 12-year-old children. Journal of the American Academy of Child & Adolescent Psychiatry, 36, 503-514.

33.

Ercan

E. S.

Amado

Somer

Çıkoğlu

(2001). A work for developing a test for attention deficit hyperactivity disorder and disruptive behaviours disorders. Turkish Journal of Child and Adolescent Mental Health, 8, 132-144.

34.

Ercan

E. S.

Ardic

U. A.

Kutlu

Durak

(2012). No beneficial effects of adding parent training to methylphenidate treatment for ADHD + ODD/CD children: A 1-year prospective follow-up study. Journal of Attention Disorders, 18, 145-157.

35.

Ercan

E. S.

Kandulu

Uslu

Ardic

U. A.

Yazici

K. U.

Basay

B. K.

… Rohde

L. A.

(2013). Prevalence and diagnostic stability of ADHD and ODD in Turkish children: A 4-year longitudinal study. Child and Adolescent Psychiatry and Mental Health, 7(1), Article 30.

36.

Erşan

E. E.

Doğan

Sümer

(2004). The distribution of symptoms of attention-deficit/hyperactivity disorder and oppositional defiant disorder in school age children in Turkey. European Child and Adolescent Psychiatry, 13, 354-361.

37.

Faraone

S. V.

Biederman

Jetton

J. G.

Tsuang

M. T.

(1997). Attention deficit disorder and conduct disorder: Longitudinal evidence for a familial subtype. Psychological Medicine, 27, 291-300.

38.

Faraone

S. V.

Biederman

Mennin

Russell

Tsuang

M. T.

(1998). Familial subtypes of attention deficit hyperactivity disorder: A 4-year follow-up study of children from antisocial-ADHD families. Journal of Child Psychology and Psychiatry, 39, 1045-1053.

39.

Faraone

S. V.

Biederman

Monuteaux

M. C.

(2001). Attention deficit hyperactivity disorder with bipolar disorder in girls: Further evidence for a familial subtype? Journal of Affective Disorder, 64(1), 19-26.

40.

Faraone

S. V. M. C.

Sergeant

Gillberg

Biederman

(2003). The worldwide prevalence of ADHD: Is it an American condition? World Psychiatry, 2, 104-113.

41.

Faraone

S. V.

Stephen

Biederman

Chen

W. J.

Milberger

Warburton

Tsuang

M. T.

(1995). Genetic heterogeneity in attention-deficit hyperactivity disorder (ADHD): Gender, psychiatric comorbidity, and maternal ADHD. Journal of Abnormal Psychology, 104, 334-345.

42.

Gadow

K. D.

Nolan

E. E.

Litcher

Carlson

G. A.

Panina

Golovakha

… Bromet

E. J.

(2000). Comparison of attention-deficit/hyperactivity disorder symptom subtypes in Ukrainian schoolchildren. Journal of the American Academy of Child & Adolescent Psychiatry, 39, 1520-1527.

43.

Gadow

K. D.

Nolan

E. E.

Sverd

Sprafkin

Schwartz

(2002). Anxiety and depression symptoms and response to methylphenidate in children with attention-deficit hyperactivity disorder and tic disorder. Journal of Clinical Psychopharmacology, 22, 267-274.

44.

Gau

S. S.

H. C.

Shang

C. Y.

Soong

W. T.

Y. Y.

Lin

L. Y.

Chiu

Y. N.

(2010). Psychiatric comorbidity among children and adolescents with and without persistent attention-deficit hyperactivity disorder. Australian & New Zealand Journal of Psychiatry, 44, 135-143.

45.

Geller

Biederman

Faraone

S. V.

Frazier

Coffey

B. J.

Kim

Bellordre

C. A.

(2000). Clinical correlates of obsessive compulsive disorder in children and adolescents referred to specialized and non-specialized clinical settings. Depression and Anxiety, 11, 163-168.

46.

Geller

Biederman

Faraone

S. V.

Cradock

Hagermoser

Zaman

… Spencer

T. J.

(2002). Attention-deficit/hyperactivity disorder in children and adolescents with obsessive-compulsive disorder: Fact or artifact? Journal of the American Academy of Child & Adolescent Psychiatry, 41, 52-58.

47.

Ghanizadeh

(2009). Psychiatric comorbidity differences in clinic-referred children and adolescents with ADHD according to the subtypes and gender. Journal of Child Neurology, 24, 679-684.

48.

Gillberg

(2004). The field of child and adolescent psychiatry. European Child and Adolescent Psychiatry, 3, 1-2.

49.

Gomez

Harvey

Quick

Scharer

Harris

(1999). DSM-IV AD/HD: Confirmatory factor models, prevalence, and gender and age differences based on parent and teacher ratings of Australian primary school children. Journal of Child Psychology and Psychiatry, 40, 265-274.

50.

Gökler

Unal

Pehlivanturk

Cengelkultur

Akdemir

Taner

(2004). Okul çağı çocukları için duygudurum bozuklukları ve şizofreni görüşme çizelgesi-şimdi ve yaşam boyu şekli-türkçe uyarlamasının geçerlik ve güvenirliği. Cocuk ve Genclik Ruh Sağlığı Dergisi, 11, 109-116.

51.

Graetz

B. W.

Sawyer

M. G.

Hazell

P. L.

Arney

Baghurst

(2001). Validity of DSM-IVADHD subtypes in a nationally representative sample of Australian children and adolescents. Journal of the American Academy of Child & Adolescence Psychiatry, 40, 1410-1417.

52.

Hergüner

(2012). Psychiatric comorbidity in children and adolescents with attention deficit hyperactivity disorder. Archives of Neuropsychiatry, 49, 114-118.

53.

Heyman

Fombonne

Simmons

Ford

Meltzer

Goodman

(2001). Prevalence of obsessive—Compulsive disorder in the British nationwide survey of child mental health. The British Journal of Psychiatry, 179, 324-329.

54.

Hinshaw

S. P.

(2002). Preadolescent girls with attention-deficit/hyperactivity disorder: I. Background characteristics, comorbidity, cognitive and social functioning, and parenting practices. Journal of Consulting & Clinical Psychology, 70, 1086-1098.

55.

Huh

Choi

Song

Kim

Hong

S. D.

Joung

(2011). A comparison of comorbidity and psychological outcomes in children and adolescents with attention-deficit/hyperactivity disorder. Psychiatry Investigation, 8(2), 95-101.

56.

Jensen

P. S.

Hinshaw

S. P.

Kraemer

H. C.

Lenora

Newcorn

J. H.

Abikoff

H. B.

… Vitiello

(2001). ADHD comorbidity findings from the MTA study: Comparing comorbid subgroups. Journal of the American Academy of Child & Adolescent Psychiatry, 40, 147-158.

57.

Jensen

P. S.

Martin

Cantwell

D. P.

(1997). Comorbidity in ADHD: Implications for research, practice, and DSM-V. Journal of the American Academy of Child & Adolescent Psychiatry, 36, 1065-1079.

58.

Joelsson

Chudal

Gyllenberg

Kesti

A. K.

Hinkka-Yli-Salomäki

Virtanen

J. P.

… Sourander

(2015). Demographic characteristics and psychiatric comorbidity of children and adolescents diagnosed with ADHD in specialized healthcare. Child Psychiatry & Human Development, 47, 574-582.

59.

Kadesjö

Gillberg

(2001). The comorbidity of ADHD in the general population of Swedish school-age children. Journal of Child Psychology and Psychiatry, 42, 487-492.

60.

Kessler

R. C.

Adler

Barkley

R. A.

Biederman

Conners

C. K.

Demler

… Zaslavsky

A. M.

(2006). The prevalence and correlates of adult ADHD in the United States: Results from the National Comorbidity Survey Replication. American Journal Psychiatry, 163, 716-723.

61.

Lahey

B. B.

Pelham

W. E.

Stein

M. A.

Loney

Trapani

Nugent

… Baumann

(1998). Validity of DSM-IV attention-deficit/hyperactivity disorder for younger children. Journal of the American Academy of Child & Adolescent Psychiatry, 37, 695-702.

62.

Larson

Russ

S. A.

Kahn

R. S.

Halfon

(2011). Patterns of comorbidity, functioning, and service use for US children with ADHD, 2007. Pediatrics, 127, 462-470.

63.

Levin-Decanini

Connolly

S. D.

Simpson

Suarez

Jacob

(2013). Comparison of behavioral profiles for anxiety-related comorbidities including ADHD and selective mutism in children. Depression and Anxiety, 30, 857-864.

64.

Levy

Hay

D. A.

Bennett

K. S.

McStephen

(2005). Gender differences in ADHD subtype comorbidity. Journal of the American Academy of Child & Adolescent Psychiatry, 44, 368-376.

65.

Liu

Sun

Uchiyama

Okawa

(2000). Attaining nocturnal urinary control, nocturnal enuresis, and behavioral problems in Chinese children aged 6 through 16 years. Journal of the American Academy of Child & Adolescent Psychiatry, 39, 1557-1564.

66.

Manassis

Tannock

Barbosa

(2000). Dichotic listening and response inhibition in children with comorbid anxiety disorders and ADHD. Journal of the American Academy of Child & Adolescent Psychiatry, 39, 1152-1159.

67.

Multimodal Treatment Study of Children With ADHD Cooperative Group (MTA). (1999). Moderators and mediators of treatment response for children with attention-deficit/hyperactivity disorder: The Multimodal Treatment Study of Children With Attention-deficit/hyperactivity disorder. Archives of General Psychiatry, 56, 1088-1096.

68.

Mukaddes

N. M.

Hergüner

Tanidir

(2010). Psychiatric disorders in individuals with high-functioning autism and Asperger’s disorder: Similarities and differences. The World Journal of Biological Psychiatry, 11, 964-971.

69.

Nussbaum

N. L.

(2012). ADHD and female specific concerns: A review of the literature and clinical implications. Journal of Attention Disorders, 16, 87-100.

70.

Pliszka

S. R.

(2003). Psychiatric comorbidities in children with attention deficit hyperactivity disorder: Implications for management. Pediatric Drugs, 5, 741-750.

71.

Polanczyk

Jensen

(2008). Epidemiologic considerations in attention deficit hyperactivity disorder: A review and update. Child and Adolescent Psychiatric Clinics of North America, 17, 245-260.

72.

Polanczyk

Silva de Lima

Horta

B. H.

Biederman

Rohde

L. A.

(2007). The worldwide prevalence of ADHD: A systematic review and metaregression analysis. American Journal of Psychiatry, 164, 942-948.

73.

Power

T. J.

Costigan

T. E.

Eiraldi

R. B.

Leff

S. S.

(2004). Variations in anxiety and depression as a function of ADHD subtypes defined by DSM-IV: Do subtype differences exist or not? Journal of Abnormal Child Psychology, 32, 27-37.

74.

Skounti

Philalithis

Galanaki

(2007). Variations in prevalence of attention deficit hyperactivity disorder worldwide. European Journal of Pediatrics, 166, 117-123.

75.

Small

D. V.

Simons

A. D.

Yovanoff

Silva

S. G.

Lewis

C. C.

Murakami

J. L.

March

. (2008). Depressed adolescents and comorbid psychiatric disorders: Are there differences in the presentation of depression? Journal of Abnormal Child Psychology, 36, 1015-1028.

76.

Spencer

Biederman

Coffey

Geller

Faraone

Wilens

(2001). Tourette disorder and ADHD. Advances in Neurology, 85, 57-77.

77.

Spencer

Biederman

Wilens

(1999). Attention-deficit/hyperactivity disorder and comorbidity. Pediatric Clinic of North America, 46, 915-927.

78.

Spetie

Arnold

E. L.

(2007). Attention-deficit/hyperactivity disorder. In Martin

Volkmar

F. R.

(Eds.), Lewis’s child and adolescent psychiatry (4th ed., pp. 430-454). Philadelphia, PA: Lippincott Williams & Wilkins.

79.

Steiner

(2007). Practice parameter for the assessment and treatment of children and adolescents with oppositional defiant disorder. Journal of the American Academy of Child & Adolescent Psychiatry, 46, 126-141.

80.

Taurines

Schmitt

Renner

Conner

A. C.

Warnke

Romanos

(2010). Developmental comorbidity in attention-deficit/hyperactivity disorder. Attention Deficit Hyperactivity Disorder, 2, 267-289.

81.

Toro

Cervera

Osejo

Salamero

(1992). Obsessive-compulsive disorder in childhood and adolescence: A clinical study. Journal of Child Psychology and Psychiatry, 33, 1025-1037.

82.

Turgay

(1994). Disruptive behavior disorders child and adolescent screening and rating scales for children, adolescents, parents and teachers. West Bloomfield, MI: Integrative Therapy Institute Publication.

83.

Turgay

(2005). Treatment of comorbidity in conduct disorder with attention-deficit hyperactivity disorder (ADHD). Essential psychopharmacology, 6, 277-290.

84.

Walsh

Menvielle

(2004). Disorders of elimination. In Wiener

J. M.

Dulcan

M. K.

(Eds.), Textbook of child and adolescent psychiatry (3rd ed., pp. 743-750). Washington, DC: American Psychiatric Publishing.

85.

Waxmonsky

(2003). Assessment and treatment of attention deficit hyperactivity disorder in children with comorbid psychiatric illness. Current Opinion in Pediatrics, 15, 476-482.

86.

Weidle

Jozefiak

Ivarsson

Thomsen

P. H.

(2014). Quality of life in children with OCD with and without comorbidity. Health and Quality of Life Outcomes, 12, 152.

87.

Wilder-Willis

K. E.

Sax

K. W.

Rosenberg

H. L.

Fleck

D. E.

Shear

P. K.

Strakowski

S. M.

(2001). Persistent attentional dysfunction in remitted bipolar disorder. Bipolar Disorders, 3, 58-62.

88.

Wilens

T. E.

Biederman

Brown

Tanguay

Monuteaux

M. C.

Blake

Spencer

T. J.

(2002). Psychiatric comorbidity and functioning in clinically referred preschool children and school-age youths with ADHD. Journal of the American Academy of Child & Adolescent Psychiatry, 41, 262-268.

89.

Willcutt

E. G.

(2012). The prevalence of DSM-IV attention-deficit/hyperactivity disorder: A meta-analytic review. Neurotherapeutics, 9, 490-499.

90.

Willcutt

E. G.

Nigg

J. T.

Pennington

B. F.

Solanto

M. V.

Rohde

L. A.

Tannock

… Lahey

B. B.

(2012). Validity of DSM-IV attention deficit/hyperactivity disorder symptom dimensions and subtypes. Journal of Abnormal Psychology, 121, 991-1010.

91.

Wyman

P. A.

Gaudieri

P. A.

Schmeelk-Cone

Cross

Brown

C. H.

Sworts

… Nathan

(2009). Emotional triggers and psychopathology associated with suicidal ideation in urban children with elevated aggressive-disruptive behavior. Journal of Abnormal Child Psychology, 37, 917-928.

92.

Yüce

Zoroğlu

S. S.

Ceylan

M. F.

Kandemir

Karabekiroğlu

(2013). Psychiatric comorbidity distribution and diversities in children and adolescents with attention deficit/hyperactivity disorder: A study from Turkey. Neuropsychiatric Disease and Treatment, 9, 1791-1799.