Methylenetetrahydrofolate Reductase Polymorphisms C677T and Risk of Autism in the Chinese Han Population

Abstract

Causes of autism are still unknown. Some studies have shown that autism might be associated with metabolic abnormalities in the folate/homocysteine pathway, which is involved in DNA methylation, thus altering gene expression. The association between the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphisms and the risk of autism is still controversial and ambiguous. The purpose of this study was to examine the effect of the MTHFR C677T polymorphism on the autism risk in the Chinese Han population. A population-based case-control study was conducted in 186 children with autism and 186 controls. The MTHFR C677T polymorphisms were determined by using a polymerase chain reaction-restriction fragment length polymorphism assay. The frequency of genotype MTHFR 677TT in children with autism (16.1%) was significantly higher (odds ratio [OR]=2.04; 95% confidence interval [CI]=1.07, 3.89; p=0.03] than those in controls (8.6%). When stratifying by select-item scores on the Autism Diagnostic Interview—Revised, it was found that children with current overactivity had a significantly higher frequency of the MTHFR 677TT genotype (OR=2.77, 95% CI=1.17, 6.60; p=0.02) than those without. This study suggested that MTHFR C677T is a risk factor of autism in Chinese Han children.

Introduction

Autism is a pervasive developmental disorder (PDD) defined behaviorally by qualitative impairments in social interaction and communication, and restricted, repetitive, and stereotyped behaviors and interests, as well as delay or abnormalities in social interaction, language, or imaginative play having onset before 3 years of age (Weiss, 2009). Autism has a prevalence of 10-60 individuals per 10,000 (Chakrabarti and Fombonne, 2001). It is recognized that autism and these autism-spectrum disorders (ASD) share essential clinical and behavioral features, although they differ in severity and age at onset (Charman, 2002). Autism is generally accepted as having a strong genetic basis, and the estimated heritability of autism exceeds 90% (Lauritsen and Ewald, 2001; Freitag, 2007).

The methylenetetrahydrofolate reductase (MTHFR) gene, located on chromosome 1 (1p36.3), encodes the MTHFR enzyme, which plays an important role in folate metabolism (Algasham et al., 2009). The MTHFR C677T polymorphism converts an alanine residue to a valine (ALA222VAL), leading to a lower enzymatic activity (Ali et al., 2009; Mansoor et al., 2009). Some studies have shown that autism might be associated with metabolic abnormalities in the folate/homocysteine pathway, which is involved in DNA methylation, thus altering gene expression (dos Santos et al., 2010). The association between the MTHFR C677T polymorphisms and risk of autism is still controversial and ambiguous (James et al., 2006; Rogers, 2008; Goin-Kochel et al., 2009; Mohammad et al., 2009; Pasca et al., 2009; dos Santos et al., 2010; Liu et al., 2011; Schmidt et al., 2011). The purpose of this study was to examine the effect of MTHFR C677T polymorphisms on autism risk in the Chinese Han population.

Materials and Methods

Study subjects

We enrolled 186 children with autism and 186 controls in the Chinese Han population. A population-based case-control study was conducted between 2009 and 2011 from the First Affiliated Hospital of WenZhou Medical College, China. All cases met the criteria for autism, Asperger's syndrome, or PDD, not otherwise specified according to the DSM-IV classification system using a standard research assessment protocol that included the autism diagnostic interview—revised (ADI-R) (Lord et al., 1994) and autism diagnostic observation schedule (Lord et al., 1989) and was diagnostically confirmed by clinician consensus. The Chinese control participants were collected from the same geographic region. The protocol of this study was approved by the Ethics Committee of the First Affiliated Hospital of WenZhou Medical College.

Genotyping

DNA was extracted from leukocytes using the phenol-chloroform method. The MTHFR C677T was determined by using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. Based on the GenBank reference sequence, the PCR primers were as follows: forward, 5′-TGAAGGAGAAGGTGTCTGCGGGA -3′; reverse, 5′-AGGACGGTGCGGTGAGAGTG -3′. The PCR products were digested with the restriction enzyme HinFI; the digestion products were then subjected to electrophoresis in a 3% agarose gel; and alleles were evaluated according to the band size. Control samples were always used from homozygous and heterozygous individuals during the RFLP procedures.

Statistical analysis

Data were analyzed using SPSS statistical package software version 17 (SPSS, Inc., Chicago, IL). The MTHFR allele and genotype frequencies in patients were compared to controls using the χ² test. The Hardy-Weinberg test of genetic equilibrium was applied using the χ² test to ensure that there was no significant difference between observed and expected genotype frequencies. A p-value was considered significant at a level of <0.05.

Results

General characteristics of children with autism and controls are listed in Table 1. No differences were observed in age, gender, height, weight, or handedness. The mean age was 8.1 (±4.3) years for the children with autism and 8.2 (±4.1) years for the controls, and 74.2% children were male in the autism group and 75.8% for the controls. This distribution of the alleles fits the Hardy-Weinberg equilibrium.

Table 1.

General Characteristics of Autism and Controls

	Autism	Controls	p-Value
Number of subjects	186	186	—
Age (years), mean±SD	8.1±4.3	8.2±4.1	0.82
Gender: male/female	138/48	141/45	0.72
Height (cm)	128.1±9.4	129.9±9.7	0.07
Weight (kg)	28.7±8.3	29.1±8.5	0.65
Handedness: right/left	186/0	186/0	1

The frequency of genotype MTHFR 677TT in children with autism (16.1%) was significantly higher (odds ratio [OR]=2.04, 95% confidence interval (CI)=1.07, 3.89; p=0.03] than those in controls (8.6%) (Table 2). When stratifying by select-item scores on the ADI-R, it was found that children with current overactivity had a significantly higher frequency of the MTHFR 677TT genotype (OR=2.77, 95% CI=1.17, 6.60; p=0.02) than those without (Table 3).

Table 2.

Genotype Frequencies of the MTHFR C677T Gene Polymorphism in Autism and Controls

Genotype	Autism (%)	Controls (%)	OR (95%CI)	p-Value
CC	79 (42.5)	87 (46.8)	0.84 (0.56, 1.27)	0.40
CT	77 (41.4)	83 (44.6)	0.88 (0.58, 1.32)	0.53
TT	30 (16.1)	16 (8.6)	2.04 (1.07, 3.89)	0.03
C allele frequency	235 (63.2)	257 (69.1)	0.77 (0.57, 1.04)	0.09
T allele frequency	137 (36.8)	115 (30.9)	1.30 (0.96, 1.77)	0.09

MTHFR, methylenetetrahydrofolate reductase; OR, odds ratio; CI, confidence interval.

Table 3.

Select-Item Scores on the ADI-R of the MTHFR C677T Genotype Frequency in Autism

			CC			CT			TT
ADI-R item	Score	Number 186	n (%)	OR (95% CI)	p-Value	n (%)	OR (95% CI)	p-Value	n (%)	OR (95% CI)	p-Value
Attention to voice	0	38 (20.4)	17 (44.7)	1 (Reference)		15 (39.5)	1 (Reference)		6 (15.8)	1 (Reference)
	1	56 (30.1)	22 (39.3)	0.88 (0.41, 1.87)	0.74	21 (37.5)	0.95 (0.44, 2.07)	0.90	13 (23.2)	1.47 (0.51, 4.21)	0.47
	2	92 (49.5)	40 (43.5)	0.97 (0.49, 1.92)	0.94	41 (44.6)	1.13 (0.56, 2.28)	0.74	11 (11.9)	0.76 (0.26, 2.20)	0.61
Direct gaze	0	20 (10.8)	8 (40.0)	1 (Reference)		7 (35.0)	1 (Reference)		5 (25.0)	1 (Reference)
	1	85 (45.7)	35 (41.2)	1.03 (0.42, 2.56)	0.95	33 (38.8)	1.11 (0.43, 2.87)	0.83	17 (20.0)	0.80 (0.26, 2.43)	0.69
	2	81 (43.5)	36 (44.4)	1.11 (0.45, 2.76)	0.82	37 (45.7)	1.31 (0.51, 3.36)	0.58	8 (9.9)	0.39 (0.12, 1.34)	0.14
Current repetitive use of objects	0	74 (39.8)	30 (40.5)	1 (Reference)		29 (39.2)	1 (Reference)		15 (20.3)	1 (Reference)
	1	56 (30.1)	25 (44.6)	1.10 (0.58, 2.08)	0.77	23 (41.1)	1.05 (0.55, 2.00)	0.89	8 (14.3)	0.71 (0.28, 1.78)	0.46
	2	56 (30.1)	24 (42.9)	1.06 (0.56, 2.00)	0.87	25 (44.6)	1.14 (0.60, 2.16)	0.69	7 (12.5)	0.62 (0.24, 1.61)	0.33
Ever repetitive use of objects	0	37 (19.9)	15 (40.6)	1 (Reference)		14 (37.8)	1 (Reference)		8 (21.6)	1 (Reference)
	1	39 (21.0)	17 (43.6)	1.08 (0.47, 2.46)	0.86	16 (41.0)	1.08 (0.47, 2.53)	0.85	6 (15.4)	0.71 (0.23, 2.25)	0.56
	2	110 (59.1)	47 (42.7)	1.05 (0.53, 2.10)	0.88	47 (42.7)	1.13 (0.56, 2.28)	0.74	16 (14.6)	0.67 (0.27, 1.70)	0.40
Current compulsions and rituals	0	96 (51.6)	40 (41.7)	1 (Reference)		39 (40.6)	1 (Reference)		17 (17.7)	1 (Reference)
	1	47 (25.3)	20 (42.6)	1.02 (0.54, 1.94)	0.95	19 (40.4)	0.99 (0.52, 1.91)	0.99	8 (17.0)	0.96 (0.39, 2.39)	0.93
	2	43 (23.1)	19 (44.2)	1.06 (0.55, 2.04)	0.86	19 (44.2)	1.09 (0.57, 2.10)	0.80	5 (11.6)	0.66 (0.23, 1.89)	0.44
Ever compulsions and rituals	0	77 (41.4)	35 (45.4)	1 (Reference)		31 (40.3)	1 (Reference)		11 (14.3)	1 (Reference)
	1	44 (23.7)	19 (43.2)	0.95 (0.49, 1.86)	0.88	17 (38.6)	0.96 (0.48, 1.93)	0.91	8 (18.2)	1.27 (0.48, 3.40)	0.63
	2	65 (34.9)	25 (38.5)	0.85 (0.46, 1.56)	0.59	29 (44.6)	1.11 (0.61, 2.03)	0.74	11 (16.9)	1.19 (0.48, 2.91)	0.71
Current hand and finger mannerisms	0	75 (40.3)	34 (45.3)	1 (Reference)		32 (42.7)	1 (Reference)		9 (12.0)	1 (Reference)
	1	67 (36.0)	28 (41.8)	0.92 (0.51, 1.68)	0.79	26 (38.8)	0.91 (0.49, 1.68)	0.76	13 (19.4)	1.62 (0.65, 4.02)	0.30
	2	44 (23.7)	17 (38.6)	0.85 (0.43, 1.70)	0.65	19 (43.2)	1.01 (0.51, 1.99)	0.97	8 (18.2)	1.52 (0.55, 4.21)	0.43
Ever hand and finger mannerisms	0	48 (25.8)	22 (45.8)	1 (Reference)		20 (41.7)	1 (Reference)		6 (12.5)	1 (Reference)
	1	48 (25.8)	21 (43.7)	0.96 (0.47, 1.96)	0.90	19 (39.6)	0.95 (0.45, 2.00)	0.89	8 (16.7)	1.33 (0.43, 4.13)	0.62
	2	90 (48.4)	36 (40.0)	0.87 (0.46, 1.65)	0.68	38 (42.2)	1.01 (0.53, 1.93)	0.97	16 (17.8)	1.42 (0.52, 3.87)	0.49
Current complex body movements	0	98 (52.7)	45 (45.9)	1 (Reference)		40 (40.8)	1 (Reference)		13 (13.3)	1 (Reference)
	1	45 (24.2)	18 (40.0)	0.87 (0.45, 1.67)	0.68	16 (35.6)	0.87 (0.44, 1.72)	0.69	11 (24.4)	1.84 (0.77, 4.43)	0.17
	2	43 (23.1)	16 (37.2)	0.81 (0.41, 1.59)	0.54	21 (48.8)	1.20 (0.63, 2.27)	0.58	6 (14.0)	1.05 (0.38, 2.95)	0.92
Ever complex body movements	0	80 (43.0)	33 (41.3)	1 (Reference)		32 (40.0)	1 (Reference)		15 (18.7)	1 (Reference)
	1	35 (18.8)	15 (42.9)	1.04 (0.50, 2.15)	0.92	15 (42.9)	1.07 (0.52, 2.23)	0.85	5 (14.2)	0.76 (0.26, 2.26)	0.62
	2	71 (38.2)	31 (43.7)	1.06 (0.59, 1.90)	0.85	30 (42.2)	1.06 (0.59, 1.91)	0.86	10 (14.1)	0.75 (0.32, 1.78)	0.52
Current aggression toward family	0	83 (44.6)	36 (43.4)	1 (Reference)		34 (40.9)	1 (Reference)		13 (15.7)	1 (Reference)
	1	50 (26.9)	22 (44.0)	1.01 (0.54, 1.92)	0.97	21 (42.0)	1.03 (0.54, 1.96)	0.94	7 (14.0)	0.89 (0.33, 2.39)	0.82
	2	53 (28.5)	21 (39.6)	0.91 (0.48, 1.73)	0.78	22 (41.5)	1.01 (0.54, 1.92)	0.97	10 (18.9)	1.21 (0.49, 2.94)	0.68
Ever aggression toward family	0	59 (31.7)	26 (44.1)	1 (Reference)		24 (40.7)	1 (Reference)		9 (15.2)	1 (Reference)
	1	34 (18.3)	15 (44.1)	1.00 (0.47, 2.15)	0.99	14 (41.2)	1.01 (0.46, 2.21)	0.98	5 (14.7)	0.96 (0.30, 3.11)	0.95
	2	93 (50.0)	38 (40.9)	0.93 (0.51, 1.68)	0.80	39 (41.9)	1.03 (0.56, 1.89)	0.92	16 (17.2)	1.13 (0.47, 2.72)	0.79
Current aggression toward others	0	117 (62.9)	51 (43.6)	1 (Reference)		48 (41.0)	1 (Reference)		18 (15.4)	1 (Reference)
	1	46 (24.7)	20 (43.5)	0.99 (0.54, 1.85)	0.99	19 (41.3)	1.01 (0.54, 1.89)	0.98	7 (15.2)	0.99 (0.39, 2.53)	0.98
	2	23 (12.4)	8 (34.8)	0.80 (0.34, 1.90)	0.61	10 (43.5)	1.06 (0.47, 2.39)	0.89	5 (21.7)	1.41 (0.48, 4.19)	0.53
Ever aggression toward others	0	100 (53.8)	44 (44.0)	1 (Reference)		40 (40.0)	1 (Reference)		16 (16.0)	1 (Reference)
	1	41 (22.0)	18 (43.9)	0.99 (0.52, 1.93)	0.99	16 (39.0)	0.98 (0.49, 1.93)	0.94	7 (17.1)	1.07 (0.41, 2.79)	0.89
	2	45 (24.2)	17 (37.8)	0.86 (0.44, 1.66)	0.65	21 (46.7)	1.17 (0.62, 2.20)	0.63	7 (15.5)	0.97 (0.37, 2.53)	0.95
Current self-injurious behavior	0	138 (74.2)	61 (44.2)	1 (Reference)		56 (40.6)	1 (Reference)		21 (15.2)	1 (Reference)
	1	19 (10.2)	8 (42.1)	0.95 (0.39, 2.29)	0.91	7 (36.8)	0.91 (0.36, 2.28)	0.84	4 (21.1)	1.38 (0.43, 4.47)	0.59
	2	29 (15.6)	10 (34.5)	0.78 (0.36, 1.70)	0.53	14 (48.3)	1.19 (0.59, 2.42)	0.63	5 (17.2)	1.13 (0.39, 3.25)	0.82
Ever self-injurious behavior	0	118 (63.4)	52 (44.1)	1 (Reference)		50 (42.4)	1 (Reference)		16 (13.5)	1 (Reference)
	1	34 (18.3)	14 (41.2)	0.93 (0.46, 1.89)	0.85	14 (41.2)	0.97 (0.48, 1.97)	0.94	6 (17.6)	1.30 (0.47, 3.58)	0.61
	2	34 (18.3)	13 (38.2)	0.87 (0.42, 1.78)	0.70	13 (38.2)	0.90 (0.44, 1.85)	0.78	8 (23.5)	1.74 (0.68, 4.40)	0.25
Current faints, fits, or blackouts	0	168 (90.3)	71 (42.3)	1 (Reference)		70 (41.6)	1 (Reference)		27 (16.1)	1 (Reference)
	1	5 (2.2)	2 (40.0)	0.95 (0.18, 4.99)	0.95	2 (40.0)	0.96 (0.18, 5.07)	0.96	1 (20.0)	1.24 (0.14, 11.07)	0.84
	2	13 (7.5)	6 (46.1)	1.09 (0.40, 2.99)	0.86	5 (38.5)	0.92 (0.32, 2.69)	0.88	2 (15.4)	0.96 (0.21, 4.48)	0.96
Ever faints, fits, or blackouts	0	160 (86.0)	68 (42.5)	1 (Reference)		66 (41.2)	1 (Reference)		26 (16.3)	1 (Reference)
	1	8 (4.3)	4 (50.0)	1.18 (0.34, 4.04)	0.80	3 (37.5)	0.91 (0.23, 3.53)	0.89	1 (12.5)	0.77 (0.09, 6.41)	0.81
	2	18 (9.7)	7 (38.9)	0.92 (0.37, 2.29)	0.85	8 (44.4)	1.07 (0.45, 2.60)	0.87	3 (16.7)	1.03 (0.28, 3.73)	0.97
Current rocking	0	140 (75.3)	60 (42.9)	1 (Reference)		58 (41.4)	1 (Reference)		22 (15.7)	1 (Reference)
	1	30 (16.1)	13 (43.3)	1.01 (0.49, 2.07)	0.98	12 (40.0)	0.97 (0.46, 2.02)	0.93	5 (16.7)	1.06 (0.37, 3.03)	0.91
	2	16 (8.6)	6 (37.5)	0.88 (0.33, 2.35)	0.79	7 (43.8)	1.06 (0.41, 2.70)	0.91	3 (18.7)	1.19 (0.32, 4.43)	0.79
Ever rocking	0	130 (69.9)	56 (43.1)	1 (Reference)		54 (41.5)	1 (Reference)		20 (15.4)	1 (Reference)
	1	21 (11.3)	10 (47.6)	1.11 (0.49, 2.50)	0.81	8 (38.1)	0.92 (0.38, 2.20)	0.85	3 (14.3)	0.93 (0.25, 3.40)	0.91
	2	35 (18.8)	13 (37.1)	0.86 (0.42, 1.75)	0.68	15 (42.9)	1.03 (0.52, 2.04)	0.93	7 (20.0)	1.30 (0.51, 3.32)	0.58
Current overactivity	0	98 (52.7)	46 (46.9)	1 (Reference)		42 (42.9)	1 (Reference)		10 (10.2)	1 (Reference)
	1	53 (28.5)	17 (32.1)	0.68 (0.36, 1.31)	0.25	21 (39.6)	0.93 (0.50, 1.72)	0.80	15 (28.3)	2.77 (1.17, 6.60)	0.02
	2	35 (18.8)	16 (45.7)	0.97 (0.49, 1.94)	0.94	14 (40.0)	0.93 (0.46, 1.91)	0.85	5 (14.3)	1.40 (0.45, 4.38)	0.56
Ever overactivity	0	71 (38.2)	30 (42.3)	1 (Reference)		29 (40.8)	1 (Reference)		12 (16.9)	1 (Reference)
	1	50 (26.9)	21 (42.0)	0.99 (0.51, 1.93)	0.99	19 (38.0)	0.93 (0.47, 1.84)	0.84	10 (20.0)	1.18 (0.47, 2.95)	0.72
	2	65 (34.9)	28 (43.1)	1.02 (0.55, 1.89)	0.95	29 (44.6)	1.09 (0.59, 2.02)	0.78	8 (12.3)	0.73 (0.28, 1.89)	0.52

ADI-R, Autism Diagnostic Interview—Revised.

Discussion

This study found that the frequency of genotype MTHFR 677TT in children with autism was significantly higher than those in controls. When stratifying by select-item scores on the ADI-R, it was found that children with current overactivity had a significantly higher frequency of the MTHFR 677TT genotype than those without. These results were consistent with those of other studies (Goin-Kochel et al., 2009; Pasca et al., 2009).

Many studies have investigated the association between genetic polymorphisms and the risk of autism (Weiss, 2009). The study by Guerini et al. (2011b) showed that single-nucleotide polymorphisms (SNPs) of the synaptosomal-associated protein of 25-kDa gene are associated with hyperactivity in ASD. Results of a family-based linkage study found that HLA polymorphisms were associated with ASD in Italian children (Guerini et al., 2011a). Gebril and Meguid (2011) reported on the first pilot study of the possible genetic association between autism and HFE gene polymorphisms among Egyptians. A family-based association test (FBAT) in 151 Korean trios demonstrated a statistically significant association between autism and SNPs in the promoter region of the arginine vasopressin receptor 1A gene (Yang et al., 2010b). Intronic SNPs of engrailed homeobox 2 modulated the disease vulnerability of autism in a Chinese Han population (Yang et al., 2010a). Polymorphisms in leucine-rich repeat genes were associated with ASD susceptibility in populations of European ancestry (Sousa et al., 2010). An FBAT and a population-based case-control test conducted by Liu et al. (2010) found that the oxytocin receptor gene polymorphisms were associated with ASD in the Japanese population. The results of FBAT suggested that CNTNAP2 was a susceptibility gene of autism in the Chinese Han population (Li et al., 2010). Allelic variation in the glutamate transporter gene may be a biomarker for or modifier of anxiety symptom severity in children with ASD (Gadow et al., 2010b). The dopamine D4 receptor gene allelic variation may be a prognostic biomarker for challenging behaviors in children with ASD (Gadow et al., 2010a). The result of an FBAT provided significant, but weak evidence for an association between nitric oxide synthase-IIA polymorphisms and ASD in the Korean population (Kim et al., 2009).

The association between the MTHFR C677T polymorphism and other diseases has been much studied. The MTHFR 677T homozygotes showed a significant association with nonsyndromic cleft lip with or without cleft palate; 677CT heterozygotes are minor risk factors in an Indian population (Ali et al., 2009). A population-based study from Sivas and Canakkale found that the MTHFR C677T polymorphisms were significantly associated with essential hypertension in a Turkish population (Demirel et al., 2011). The data from a case-control study suggested that MTHFR C677T and A1298C could be important genetic factors predisposing to infertility in Brazilian infertile men (Gava et al., 2011). The MTHFR C677T polymorphisms were related with hematologic toxicity and hepatotoxicity and could be suggested as prognostic factors for these adverse events in Cretan children with acute lymphoblastic leukemia (Karathanasis et al., 2011). A study among an endogamous group found that MTHFR C677T polymorphisms were significantly associated with early recurrent pregnancy loss in North India (Mukhopadhyay et al., 2009). There was strong association between MTHFR C677T and maternal risk of Down syndrome in Jordanian mothers younger than 35 years (Sadiq et al., 2011). It was proved that MTHFR C677T polymorphisms were significantly associated with metabolic syndrome in the Greek population (Vasilopoulos et al., 2011).

The mechanisms of MTHFR C677T polymorphisms as a risk factor of autism are still unclear. Many studies have suggested that autism may be associated with metabolic abnormalities in the folate/homocysteine pathway, which is involved in DNA methylation, thus altering gene expression. One of the most important polymorphisms in this pathway is C677T of the MTHFR gene, because the T allele is associated with a decrease in the enzymatic activity (dos Santos et al., 2010). The association between the MTHFR C677T polymorphisms and the risk of autism is still controversial and ambiguous (James et al., 2006; Rogers, 2008; Goin-Kochel et al., 2009; Mohammad et al., 2009; Pasca et al., 2009; dos Santos et al., 2010; Liu et al., 2011; Schmidt et al., 2011). One of the reasons is that the distribution of the 677C>T allele showed regional and ethnic variations (Wilcken et al., 2003). For example, in the Americas, the frequency of the homozygous TT genotype was higher in Mexico (32%), intermediate in Atlanta (11% among whites), and somewhat lower in Alberta (6%). Genotype varied by ethnicity as well as by the geographical location (Wilcken et al., 2003). For example, TT homozygosity was more common among newborns from Mexico or those born in Atlanta of Hispanic origin, intermediate among newborns of European ancestry, and lower among newborns of African ancestry. However, a range of genotype frequencies was evident even within broad ethnic groups (Wilcken et al., 2003). For example, TT homozygosity among whites ranged from as low as 6% in Alberta (Canada), to 7.5% in New South Wales (Australia), to 11% in Atlanta (United States), to the high values already noted for Italy (Wilcken et al., 2003).

In conclusion, our study suggested that MTHFR C677T is a risk factor of autism in Chinese Han children. These data highlight the necessity of further investigation of the association between folate metabolism and problem behaviors among children with autism.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

References

Algasham

, Ismail

, Dewaidar

et al. 2009. Methylenetetrahydrofolate reductase and angiotensin-converting enzyme gene polymorphisms among Saudi population from Qassim region. Genet Test Mol Biomarkers, 13:817-820.

Ali

, Singh

, Raman

. 2009. MTHFR 677TT alone and IRF6 820GG together with MTHFR 677CT, but not MTHFR A1298C, are risks for nonsyndromic cleft lip with or without cleft palate in an Indian population. Genet Test Mol Biomarkers, 13:355-360.

Chakrabarti

, Fombonne

. 2001. Pervasive developmental disorders in preschool children. JAMA, 285:3093-3099.

Charman

. 2002. The prevalence of autism spectrum disorders. Recent evidence and future challenges. Eur Child Adolesc Psychiatry, 11:249-256.

Demirel

, Dogan

, Uludag

et al. 2011. Combined effect of Factor V Leiden, MTHFR, and angiotensin-converting enzyme (insertion/deletion) gene mutations in hypertensive adult individuals: a population-based study from Sivas and Canakkale, Turkey. Genet Test Mol Biomarkers, 15:785-791.

dos Santos

, Longo

, Brandalize

et al. 2010. MTHFR C677T is not a risk factor for autism spectrum disorders in South Brazil. Psychiatr Genet, 20:187-189.

Freitag

. 2007. The genetics of autistic disorders and its clinical relevance: a review of the literature. Mol Psychiatry, 12:2-22.

Gadow

, Devincent

, Olvet

et al. 2010a. Association of DRD4 polymorphism with severity of oppositional defiant disorder, separation anxiety disorder and repetitive behaviors in children with autism spectrum disorder. Eur J Neurosci, 32:1058-1065.

Gadow

, Roohi

, DeVincent

et al. 2010b. Glutamate transporter gene (SLC1A1) single nucleotide polymorphism (rs301430) and repetitive behaviors and anxiety in children with autism spectrum disorder. J Autism Dev Disord, 40:1139-1145.

10.

Gava

, Chagas Ede

, Bianco

et al. 2011. Methylenetetrahydrofolate reductase polymorphisms are related to male infertility in Brazilian men. Genet Test Mol Biomarkers, 15:153-157.

11.

Gebril

, Meguid

. 2011. HFE gene polymorphisms and the risk for autism in Egyptian children and impact on the effect of oxidative stress. Dis Markers, 31:289-294.

12.

Goin-Kochel

, Porter

, Peters

et al. 2009. The MTHFR 677C—>T polymorphism and behaviors in children with autism: exploratory genotype-phenotype correlations. Autism Res, 2:98-108.

13.

Guerini

, Bolognesi

, Chiappedi

et al. 2011a. HLA polymorphisms in Italian children with autism spectrum disorders: results of a family based linkage study. J Neuroimmunol, 230:135-142.

14.

Guerini

, Bolognesi

, Chiappedi

et al. 2011b. SNAP-25 single nucleotide polymorphisms are associated with hyperactivity in autism spectrum disorders. Pharmacol Res, 64:283-288.

15.

James

, Melnyk

, Jernigan

et al. 2006. Metabolic endophenotype and related genotypes are associated with oxidative stress in children with autism. Am J Med Genet B Neuropsychiatr Genet, 141B:947-956.

16.

Karathanasis

, Stiakaki

, Goulielmos

et al. 2011. The role of the methylenetetrahydrofolate reductase 677 and 1298 polymorphisms in Cretan children with acute lymphoblastic leukemia. Genet Test Mol Biomarkers, 15:5-10.

17.

Kim

, Cho

, Kim

et al. 2009. Family-based association study between NOS-I and -IIA polymorphisms and autism spectrum disorders in Korean trios. Am J Med Genet B Neuropsychiatr Genet, 150B:300-306.

18.

Lauritsen

, Ewald

. 2001. The genetics of autism. Acta Psychiatr Scand, 103:411-427.

19.

, Hu

, He

et al. 2010. Association analysis of CNTNAP2 polymorphisms with autism in the Chinese Han population. Psychiatr Genet, 20:113-117.

20.

Liu

, Kawamura

, Shimada

et al. 2010. Association of the oxytocin receptor (OXTR) gene polymorphisms with autism spectrum disorder (ASD) in the Japanese population. J Hum Genet, 55:137-141.

21.

Liu

, Solehdin

, Cohen

et al. 2011. Population- and family-based studies associate the MTHFR gene with idiopathic autism in simplex families. J Autism Dev Disord, 41:938-944.

22.

Lord

, Rutter

, Goode

et al. 1989. Autism diagnostic observation schedule: a standardized observation of communicative and social behavior. J Autism Dev Disord, 19:185-212.

23.

Lord

, Rutter

, Le Couteur

. 1994. Autism diagnostic interview-revised: a revised version of a diagnostic interview for caregivers of individuals with possible pervasive developmental disorders. J Autism Dev Disord, 24:659-685.

24.

Mansoor

, Mazhar

, Ali

et al. 2009. Prevalence of the C677T single-nucleotide polymorphism in the methylenetetrahydrofolate reductase gene among Pakistani ethnic groups. Genet Test Mol Biomarkers, 13:521-526.

25.

Mohammad

, Jain

, Chintakindi

et al. 2009. Aberrations in folate metabolic pathway and altered susceptibility to autism. Psychiatr Genet, 19:171-176.

26.

Mukhopadhyay

, Saraswathy

, Ghosh

. 2009. MTHFR C677T and factor V Leiden in recurrent pregnancy loss: a study among an endogamous group in North India. Genet Test Mol Biomarkers, 13:861-865.

27.

Pasca

, Dronca

, Kaucsar

et al. 2009. One carbon metabolism disturbances and the C677T MTHFR gene polymorphism in children with autism spectrum disorders. J Cell Mol Med, 13:4229-4238.

28.

Rogers

. 2008. Has enhanced folate status during pregnancy altered natural selection and possibly Autism prevalence? A closer look at a possible link. Med Hypotheses, 71:406-410.

29.

Sadiq

, Al-Refai

, Al-Nasser

et al. 2011. Methylenetetrahydrofolate reductase polymorphisms C677T and A1298C as maternal risk factors for Down syndrome in Jordan. Genet Test Mol Biomarkers, 15:51-57.

30.

Schmidt

, Hansen

, Hartiala

et al. 2011. Prenatal vitamins, one-carbon metabolism gene variants, and risk for autism. Epidemiology, 22:476-485.

31.

Sousa

, Clark

, Holt

et al. 2010. Polymorphisms in leucine-rich repeat genes are associated with autism spectrum disorder susceptibility in populations of European ancestry. Mol Autism, 1:7.

32.

Vasilopoulos

, Sarafidou

, Bagiatis

et al. 2011. Association between polymorphisms in MTHFR and APOA5 and metabolic syndrome in the Greek population. Genet Test Mol Biomarkers, 15:613-617.

33.

Weiss

. 2009. Autism genetics: emerging data from genome-wide copy-number and single nucleotide polymorphism scans. Expert Rev Mol Diagn, 9:795-803.

34.

Wilcken

, Bamforth

, Li

et al. 2003. Geographical and ethnic variation of the 677C>T allele of 5,10 methylenetetrahydrofolate reductase (MTHFR): findings from over 7000 newborns from 16 areas world wide. J Med Genet, 40:619-625.

35.

Yang

, Shu

, Hallmayer

et al. 2010a. Intronic single nucleotide polymorphisms of engrailed homeobox 2 modulate the disease vulnerability of autism in a Han Chinese population. Neuropsychobiology, 62:104-115.

36.

Yang

, Cho

, Yoo

et al. 2010b. Association study between single nucleotide polymorphisms in promoter region of AVPR1A and Korean autism spectrum disorders. Neurosci Lett, 479:197-200.