Preverbal skills in 8-month-old children with sex chromosome trisomies

Abstract

Individuals with sex chromosome trisomies (SCTs) have an increased risk of language delays and impairments. However, there are only a few data relative to their language development in early childhood. The present study aimed to investigate the preverbal skills shown by a group of 8-month-old children with SCTs to assess the presence of a possible early communicative delay. Moreover, the predictive role of early preverbal productions on later lexical development at 24 months was analysed. Twenty-six children with SCTs and 24 typically developing (TD) children participated in the study. Their use of vocal productions and gazes addressed to the communicative partner was assessed during a parent–child observation session held when the children were 8 months old. In addition, the children’s word comprehension at 8 months and their word production at 24 months were indirectly assessed by a parental report. Children’s word comprehension was similar in the two groups of children, whereas a significantly lower frequency per minute of gazes was found in children with SCTs than in TD children. A significantly lower proportion of children with SCTs showed the ability to produce babbling during the observation session, and significant differences were also found in the frequency of babbling utterances. No significant differences emerged among the subgroups of children with different types of SCTs. The predictive role of babbling on later lexical size was found in TD children but not in children with SCTs. This result could be probably explained by the small number of children in this group who could produce babbling utterances. The study leads to identify early signals of delay in the preverbal skills of children with SCTs. Early monitoring of their communicative development could help the clinicians in intervening with well-timed and targeted programmes.

Keywords

Preverbal babbling Klinefelter syndrome triple X syndrome XYY syndrome predictor

Introduction

Sex chromosome trisomies (SCTs) are genetic syndromes characterised by an extra sex chromosome to a normal karyotype. Three different syndromes can be identified: triple X syndrome (XXX), in females with 47, XXX karyotype; Klinefelter syndrome (XXY), in males with 47, XXY karyotype; and double Y syndrome (XYY), in males with 47, XYY karyotype.

The most common SCT is XXY, with an estimated prevalence from 1 in 426 to 1 in 1000 male births (Bojesen et al., 2003; Herlihy et al., 2011), whereas XXX and XYY syndromes appear to have an estimated prevalence of 1 in 1000 same-sex individuals (Messer et al., 2013; Ross et al., 2009). However, these data may be underestimated because several cases remain undiagnosed due to their mild phenotype (Bishop et al., 2011; Leggett et al., 2010).

XXY was first described as a disorder characterised by infertility, hypogonadism, gynecomastia and increased gonadotropin levels (Klinefelter et al., 1942). Individuals with XXY usually present tall stature and endocrine dysfunction. They can show an atypical neuropsychological profile that may include language impairments, learning disabilities, attentional and executive deficits, impaired social abilities and atypical motor development (Bishop et al., 2011; Ross et al., 2008; Simpson et al., 2003; St John et al., 2019). The IQ appears to have a normal distribution, but with the mean score slightly shifted to the left, and verbal abilities more depressed than the performance ones (Bender et al., 1986). Concerning linguistic skills, a high percentage of children with XXY shows delays and impairments in different domains of language development (St John et al., 2019; Verri et al., 2010; Zampini, Burla, et al., 2018; Zampini, Draghi, et al., 2018).

The phenotype of individuals with XYY shares with that of males with XXY some physical and cognitive characteristics, for instance, tall stature and characteristic cognitive attributes but there is no testicular failure (Ross et al., 2009). Similar to individuals with XXY, the general intelligence is usually in the normal range, with the mean slightly shifted to the left (Bender et al., 1984; Netley, 1986) and with possible deficits in verbal IQ relative to comparison groups (Leggett et al., 2010). Moreover, as in XXY syndrome, boys with XYY have an increased risk of delayed and impaired language development (Bender et al., 1984; Ratcliffe, 1982; Ross et al., 2009), hyperactivity and attention problems (Ruud et al., 2005), and consequent learning difficulties (Bender et al., 1984; Netley, 1986; Ross et al., 2009). Linden and Bender (2002) registered a delayed motor development and lack of motor coordination, that was confirmed by Ross et al. (2009), but that appeared to be less pervasive than in XXY.

XXX has some developmental and psychological characteristics in common with the other two SCTs, such as delays in motor development, principally related to hypotonia, and in language development (Bishop et al., 2011; Messer et al., 2013; Tartaglia et al., 2010). Concerning the IQ, girls with XXX usually show cognitive skills in the low average range, and intellectual and learning disabilities are more common than in the general population (Bishop et al., 2019; Tartaglia et al., 2010). A decrease in verbal domains relative to non-verbal ones can be present, but often both verbal and non-verbal abilities appear impaired (Leggett et al., 2010). Attentional problems and poor executive function are frequently detected (Bender et al., 1993; Pennington et al., 1980).

As reported above, according to the literature, individuals with XXY, XYY and XXX have an increased risk of language impairments (Bishop et al., 2019). However, there are only a few data on language development in early childhood (e.g. Samango-Sprouse, 2001; Zampini, Burla, et al., 2018; Zampini, Draghi, et al., 2018). In the study of Samango-Sprouse (2001; Samango-Sprouse & Law, 2001), the presence of a speech delay was found by 12 months in children with XXY: infants were reported to show delayed babbling and phonological development and problems in orofacial musculature coordination. The first words usually appear between 18 and 24 months in children with XXY (Simpson et al., 2003), and at around 18.5 months in children with XXX (Linden et al., 1988) rather than around 12 months as in typically developing (TD) children. In addition, at 18 months, children with XXY show a lower competence than TD peers in both lexical skills and emergent syntactic abilities (Zampini, Burla, et al., 2018). The delay in vocabulary development persists at 24 months; in fact, 60% of children with SCTs (75% of males with XXY and 43% of females with XXX) have a vocabulary size below the 5th percentile (Zampini, Draghi, et al., 2018).

The observation of early preverbal productions is relevant considering that the continuity between babbling and language development has been widely demonstrated (MacNeilage et al., 1997; Vihman et al., 2009) and early vocalisations appear to have an important role in the prediction of later lexical development (Morgan & Wren, 2018). In particular, the number of preverbal productions (McCune & Vihman, 2001), the complexity of babbling (D’Odorico et al., 2011; Fasolo et al., 2008) and its phonological characteristics, such as the consistent use of specific consonants (Keren-Portnoy et al., 2009; McCune & Vihman, 2001), have been reported as significant predictors of first lexical development. Moreover, late onset of babbling (Oller et al., 1999) and atypical characteristics of babbling production (Stoel-Gammon, 1989) have been suggested as valuable markers for later language delays, as well as possible indicators for the identification of developmental disorders that are usually detected later in childhood (Lang et al., 2019).

The emergence of canonical babbling (i.e. syllabic productions with combinations of vowels and consonants) usually occurs between 5 and 10 months in TD children (Fagan, 2009; Oller, 1980). Reduplicated babbling (i.e. the repetition of the same syllable) has been reported between the onset of canonical babbling and the emergence of referential communication (Fagan, 2009). Moreover, a decrease in reduplicated babbling has been observed in association with first words use (Karousou & López-Ornat, 2013). Babbling utterances can also contain different consonants (i.e. variegated babbling), and the emergence of this behaviour has been identified as a later and more complex level of preverbal production (Oller, 1980). The hypothesis of a strict sequential appearance of reduplicated and variegated babbling is not universally accepted since reduplicated and variegated babbling could co-occur (Mitchell & Kent, 1990). However, a significant increase in variegated babbling has been observed later in vocal development (around 11–14 months) (Karousou & López-Ornat, 2013; MacNeilage et al., 1997).

The phonetic features of babbling tend to be consistent throughout different languages, as accounted by the current articulatory explicative model (Davis & MacNeilage, 1995), with some variation between languages that could be explained in terms of specific characteristics of the input (de Boysson-Bardies & Vihman, 1991). Between 7 and 12 months, the most common manners of production reported are oral stops and nasal, and the places of articulation predominantly used are bilabial and alveolar followed by velar (Robb & Bleile, 1994). This trend has also been confirmed in Italian children since labial stops (p/b) have been identified to be the most consistently used consonants, followed by alveolar stops (t/d), nasals (m/n) and velar stops (k/g) (D’Odorico et al., 2011; Majorano et al., 2014).

Aims

There is an agreement in the literature that children with SCTs frequently show a delay in the early stages of lexical development and an increased risk of language impairments (Bishop et al., 2019; Simpson et al., 2003; Zampini, Draghi, et al., 2018). The present study aimed to investigate the preverbal skills shown by a group of 8-month-old children with SCTs to assess if some delays are already evident at an early stage of language development. The use of spontaneous vocal productions, the use of gazes addressed to the communicative partner and lexical comprehension were evaluated in consideration of their role as early predictors of language development in TD children. We aimed to analyse both the differences between the preverbal skills of children with SCTs and TD peers and the differences among the skills showed by children with XXY, XYY and XXX. In addition, in order to assess the possible predictive role of preverbal productions on later language development, the correlations between preverbal skills at 8 months and children’s expressive vocabulary production at 24 months were computed. The early identification of delays in the children’s communicative skills could help the clinicians in the management of these children to define early and tailored rehabilitative interventions.

Methods

Participants

Participants included in the study were fifty 8-month-old children, 26 with SCTs (10 females) (chronological age: M = 8.15; SD = .54; range = 7–9) and 24 TD children (10 females) (chronological age: M = 8.29; SD = .55; range = 7–9). The children with SCTs were recruited through individual contact with families referred to the Child and Adolescent Neuropsychiatric Unit of the Foundation IRCCS Ca’ Granda Ospedale Maggiore Policlinico (Milan, Italy), where they were participating in a monitoring programme. The TD children were selected from a sample of children who were participating in a longitudinal research project on early language development at the Department of Psychology of the University of Milano-Bicocca (Milan, Italy). All children with SCTs were prenatally diagnosed by amniocentesis or chorionic villus: 9 children had a diagnosis of XXY, 7 had a diagnosis of XYY syndrome and 10 had a diagnosis of XXX. None of the participants, with either SCTs or TD, had additional genetic or neurological conditions. They all had normal hearing and no history of ear infections, and they all belong to monolingual Italian-speaking families. The mothers in the two groups did not significantly differ in their number of years of education (TD: M = 17.04; SD = 1.73; range = 13–18; SCT: M = 15.31; SD = 3.23; range = 8–18; U = 232; p = .07; η² = .07). Children’s parents signed a written informed consent form before inclusion in the study.

The mean developmental quotient (DQ), assessed by the Griffiths Mental Development Scales (Griffiths & Huntley, 2007) was 96.15 (SD = 8.73; range = 79–113) in children with SCTs and 107.92 (SD = 7.57; range = 92–124) in TD children. The DQ was significantly lower in children with SCTs than in TD children (U = 96.5; p < .001; η² = .36). This difference in the children’s psychomotor development is consistent with data in the literature. Data on the DQs obtained in the five subscales of the Griffiths Mental Development Scales (i.e. Locomotor Scale, Personal-social Scale, Language Scale, Eye and Hand Coordination Scale, and Performance Scale) are reported in Table 1. All the DQs were significantly lower in children with SCTs than in TD children except for the Personal-social DQ, which was not significantly different between groups. Considering the subgroups of children with SCTs, the mean DQ was 96.56 (SD = 6.31; range = 88–106) in children with XXY, 98.71 (SD = 10.03; range = 86–113) in children with XYY and 94.00 (SD = 9.96; range = 79–108) in children with XXX. This difference was not statistically significant (H = .67; p = .72; E² = .04). Data on the DQs obtained in the five subscales of the Griffiths Mental Development Scales by children in the three subgroups of SCTs are reported in Table 2.

Table 1.

Developmental quotient (DQ) in each subscale of the Griffiths Mental Development Scales of children with SCTs and TD children.

	SCT (n = 23^a)			TD (n = 19^a)			U	p	η²
	M	SD	Range	M	SD	Range	U	p	η²
Locomotor DQ	92.57	14.76	69–129	105.32	14.92	79–134	110	.006	.18
Personal-social DQ	108.30	13.60	75–138	107.84	11.13	91–128	218	.990	.01
Language DQ	90.87	12.41	63–113	104.89	14.55	73–121	95	.002	.24
Eye and Hand Coordination DQ	94.39	15.44	63–125	106.21	12.87	79–128	115	.009	.17
Performance DQ	95.09	14.78	63–119	109.53	12.04	87–134	98.5	.002	.23

DQ: developmental quotient; SCT: sex chromosome trisomy; TD: typically developing; SD: standard deviation.

Data on the Griffiths subscales are not available for all the participants.

Note. “p” is the significance value for bold values.

Table 2.

Developmental Quotient (DQ) in each subscale of the Griffiths Mental Development Scales of children in the three subgroups of SCTs.

	XXY (n = 8^a)			XYY (n = 7^a)			XXX (n = 8^a)			H	p	E ²
	M	SD	Range	M	SD	Range	M	SD	Range	H	p	E ²
Locomotor DQ	87.25	14.54	69–107	101.57	17.19	75–129	90.00	9.93	75–106	3.38	.185	.16
Personal-social DQ	113.00	12.35	100–138	107.71	10.44	100–129	104.13	17.03	75–125	1.40	.496	.06
Language DQ	87.25	6.43	75–95	98.57	8.94	88–112	87.75	16.99	63–113	4.51	.105	.20
Eye and Hand Coordination DQ	98.00	14.56	76–113	90.86	16.12	63–113	93.87	16.93	69–125	.96	.620	.05
Performance DQ	97.13	14.81	76–117	95.00	13.98	69–112	93.12	17.06	63–119	.24	.886	.01

DQ: developmental quotient; SCT: sex chromosome trisomy; SD: standard deviation.

Data on the Griffiths subscales are not available for all the participants.

Procedure

The children’s preverbal skills at 8 months were assessed both indirectly, through a questionnaire, and directly, by analysing the spontaneous communicative acts produced during a parent–child play session. Parents filled out the Italian version of the MacArthur–Bates Communicative Development Inventories – Words and Gestures Form (Il Primo Vocabolario del Bambino [PVB] – Caselli & Casadio, 1995). This inventory provides indices of word comprehension and production and gesture use in children from 8 to 17 months. In the present study, due to the young age of the participants, only the number of words comprehended was considered.

In addition, 15-minute semi-structured play sessions (M = 15.29 minutes; SD = .82; range = 12–17) were video-recorded to assess the children’s spontaneous communicative productions. All the children participated in the play session with their mothers except for six children who participated with their fathers. Parents were instructed to play normally with their children using all the available toys (some rubber animals, a little train, two rattles and a jack-in-the-box). The parent–child dyads were alone in a room with a unidirectional mirror, and they were recorded by a video camera controlled by the examiner observing from behind the mirror. After about 7 minutes, some illustrated books were introduced, but the children were able to play with all the toys presented. Children’s vocal productions and gazes towards their parents were transcribed in CHAT format (MacWhinney, 2000).

Linguistic outcome at 24 months was assessed indirectly through the PVB (words and sentences form, for children ranging in age from 18 to 36 months). In particular, we considered the number of words spontaneously produced by children as a measure of vocabulary size. Owing to drop-out, data at 24 months were available for 39 participants: 18 TD children and 21 children with SCTs.

Coding and measures of the semi-structured play sessions at 8 months

The total number of vocal productions, excluding crying, whining and vegetative sounds (e.g. breathing, burping) (see Adams et al., 2018) was computed for each child. These vocal productions were classified using the following coding scheme (based on the traditional classifications of Oller, 1980; Stark, 1980):

Simple preverbal, that is, communicative grunts (e.g. ‘mh’) and vocalisations (e.g. ‘oh’);

Babbling, that is, vocal productions constituted by consonant–vowel combinations. These productions were further divided into

(a) Canonical Babbling (e.g. ‘da’), that is, a simple consonant–vowel combination;

(b) Reduplicated Babbling (e.g. ‘dada’), that is, the repetition of the same consonant–vowel combination;

(c) Variegated Babbling (e.g. ‘dapa’ or ‘dade’), that is, a chain of consonant–vowels combinations with at least two different consonants or vowels.

For each child, we computed the frequency per minute of the total vocal productions and the vocal productions in each category. Moreover, the babbling productions were phonologically transcribed to analyse the consonant phonemes produced by the children in the two groups. For each child who showed the ability to produce babbling utterances (i.e. a child who produced at least one babbling utterance), we computed the number of different consonant phonemes produced.

In addition, to assess the children’s preverbal skills, we also considered the number of gazes addressed to the communicative partner by the child. We noted each occurrence of gaze directed to the face of the partner during the play session, and we computed the frequency per minute.

Reliability

A trained person, blinded to group status, did the transcription and coding. The intercoder reliability was assessed in 20% of the sessions using the coding of another person blinded to group status. We used intra-class correlation coefficients (ICC) to assess reliability. The ICC was .97 (with a 95% confidence interval from .86 to .99) for simple preverbal and 1 for babbling productions. The ICC was .97 (with a 95% confidence interval from .82 to .99) for gaze production.

Data analyses

Statistical analyses were performed using IBM SPSS version 26. We used non-parametric tests due to the small number of participants and because the assumptions about normality of the distribution were not satisfied. To assess if there were differences between the two groups in the reaching of the babbling stage, the number of children who showed the ability of babbling (i.e. those who produced at least one babbling utterance) in each group was compared using the Chi-square test. In addition, the differences in the preverbal skills of the two groups of children were assessed using the Mann–Whitney non-parametric test for two independent samples to compare word comprehension, and the frequency of production of vocal utterances and gazes addressed to the partner in children with SCTs and TD children. In addition, for those children who showed the ability to produce babbling utterances, we analysed the number and type of phonemes used in the two groups.

Moreover, the possible differences in the preverbal skills of children with XXY, XYY and XXX were assessed using the Chi-square test to compare the number of children who were able to babble in each of the three subgroups and the Kruskal–Wallis test (non-parametric test for k independent samples) to compare word comprehension and the frequency of vocal and gaze production.

Finally, we used the Mann–Whitney non-parametric test for two independent samples to assess the difference in the outcome measure PVB expressive vocabulary at 24 months between SCT and TD groups. The predictive value of preverbal productions on the outcome variable in the two groups was tested estimating non-parametric correlations (Spearman’s Rho) between the frequency of production of preverbal utterances and PVB expressive vocabulary, in the two groups.

Results

Comparison between TD children and children with SCTs at 8 months

All relevant data are available in OSF (https://osf.io/8sm35/). Since from a developmental perspective, the presence or absence of babbling utterances could be informative on the children’s linguistic stage, we divided the children of the two groups (i.e. SCT vs TD) into two subgroups: those who showed the ability to produce babbling during the observation session (i.e. those who produced at least one babbling utterance) and those who did not. Only 5 out of 24 TD children (21%) did not produce babbling during the session, whereas 16 out of 26 children with SCTs (62%) did not. This difference was statistically significant (χ² = 8.49; p < .01).

Children’s word comprehension, as assessed by PVB, was similar in the two groups of children. The mean number of words comprehended was 19.00 (SD = 19.10; range = 0–77) in children with SCTs and 18.91 (SD = 20.51; range = 0–70) in children with TD. No significant differences emerged between the two groups (U = 242.5; p = .81; η² < .01).

Concerning the frequencies per minute of vocal productions (see Table 3), no significant differences were found between groups in the total frequency of vocal productions or in the frequency of simple preverbal communicative acts. A significant difference emerged in the production of babbling (U = 196; p < .02; η² = .11), with a lower frequency of babbling utterances in the SCT group than in the TD group. Considering the subcategories of babbling, statistically significant differences emerged between groups in the frequency of canonical (U = 201; p < .04; η² = .09) and reduplicated babbling (U = 215; p < .02; η² = .12), whereas no significant differences emerged in the frequency of variegated babbling, that was very small in both groups. Considering the use of gazes directed towards the communicative partner, a significantly lower frequency per minute of gazes (U = 191; p = .02; η² = .11) was found in children with SCTs than in TD children (SCT: M = .65; SD = .50; range = .07–1.63. TD: M = 1.01; SD = .54; range = .35–2.47).

Table 3.

Vocal productions (frequency per min) of children with SCTs and TD children.

	SCT (n = 26)			TD (n = 24)			U	p	η²
	M	SD	Range	M	SD	Range	U	p	η²
Total vocal productions	1.47	.92	0.06–3.72	1.90	1.09	0.38–5.67	227.5	.10	.05
Simple preverbal	1.34	.82	0.06–3.52	1.69	1.08	0.38–5.60	251.5	.24	.03
Babbling	0.13	.30	0–1.47	0.21	0.24	0–0.67	196	.02	.11
Canonical babbling	0.09	.18	0–0.80	0.12	0.14	0–0.41	212	.04	.09
Reduplicated babbling	0.03	.12	0–0.60	0.08	0.11	0–0.33	215	.02	.12
Variegated babbling	0.01	.03	0–0.13	0.02	0.05	0–0.20	307.5	.89	.01

SCT: sex chromosome trisomy; TD: typically developing; SD: standard deviation.

Note. “p” is the significance value for bold values.

The frequency of babbling productions did not appear to be significantly related to the children’s DQ either in TD children (Rho = .40; p = .054) or in children with SCTs (Rho = .11; p = .58), although the correlation approached significance for the TD group. Considering the DQ in each subscale of the Griffiths Mental Development Scales, while the relationship between babbling and the Language DQ approached significance in the TD children (Rho = .45, p = .056), for all other relationships, all Rho indices were less than .30 and all p values were greater than .22. With regard to the relationship between the frequency of gazes addressed to the partner and the children’s DQ, no significant correlations emerged in both TD children (Rho = –.03; p = .89) and children with SCTs (Rho = –.16; p = .44). Even considering the DQ in each subscale of the Griffiths Mental Development Scales, no significant correlations were found between the frequency of gazes and the DQs. All Rho indices were less than .13, and p values were greater than .08.

Phonological development in TD children and children with SCTs at 8 months

Considering only children who showed the ability to produce babbling during the interaction session (n = 29), we computed the number of different consonantal phonemes produced. Data analysis showed a similar number of consonantal phonemes in the two groups of children (SCT: M = 2.20, SD = 1.14, range = 1–5; TD: M = 1.84, SD = 1.07, range = 1–4, U = 73.50; p = .29; η² = .04). Concerning the type of consonantal phonemes produced, the majority of children in both groups used at least one labial (p/b) or dental (t/d) stop: 89% of TD children (i.e. 17 out of 19 children who produced babbling utterances) and 100% of children with SCTs (i.e. 10 out of 10 children who produced babbling utterances). A smaller number of children used back stops (k/g): 37% of TD children (i.e. 7 out of 19 children) and 30% in children with SCTs (i.e. 3 out of 10 children). Fewer children used nasals (m/n): 11% of TD children (i.e. 2 out of 19 children) and 20% in children with SCTs (i.e. 2 out of 10 children).

Comparison among subgroups of children with different SCTs

First, we considered the proportion of children in each subgroup of individuals with SCTs who did not produce babbling during the observation session. Six out of 9 children with XXY (67%), 2 out of 7 with XYY (29%), and 8 out of 10 with XXX (80%) did not produce any babbling. This difference (analysed with Likelihood Ratio test rather than chi-square test, because four cells have an expected count < 5) was not statistically significant (LR = 4.81; p = .09). In addition, no significant differences (H = .92; p = .63; E² = .01) were found in the number of words comprehended by the three subgroups of children with SCTs (XXY: M = 18, SD = 15.59, range = 3–44; XYY: M = 21, SD = 18.06, range = 2–59; XXX: M = 18, SD = 24.80, range = 0–77).

Even data concerning children’s vocal production (reported in Table 4) did not show any significant differences among the subgroups of children with SCTs. Considering also the use of gazes directed towards the communicative partner, no significant differences (H = 3.17; p = .21; E² = .08) were found among the subgroups of children with SCTs (XXY: M = .45; SD = .49; range = .07–1.63. XYY: M = .80; SD = .59; range = .13–1.60. XXX: M = .74; SD = .42; range = .19–1.53).

Table 4.

Vocal productions (frequency per min) of the children in the three subgroups of SCTs.

	XXY (n = 9)			XYY (n = 7)			XXX (n = 10)			H	p	E ²
	M	SD	Range	M	SD	Range	M	SD	Range	H	p	E ²
Total vocal productions	1.56	.84	0.53–3.25	1.59	.88	0.27–3.13	1.31	1.07	0.06–3.72	1.17	.56	.04
Simple preverbal	1.31	.65	0.53–2.81	1.46	.81	0.27–2.93	1.27	1.01	0.06–3.52	1.01	.60	.02
Babbling	0.24	.49	0–1.47	0.13	.11	0–0.31	0.03	0.07	0–0.21	3.55	.17	.10
Canonical babbling	0.15	.27	0–0.80	0.09	.12	0–0.31	0.03	0.07	0–0.21	2.33	.31	.07
Reduplicated babbling	0.07	.20	0–0.60	0.01	.02	0–0.06	0	0	0	2.26	.32	.11
Variegated babbling	0.01	.03	0–0.07	0.03	.05	0–0.13	0	0	0	3.07	.22	.01

SCT: sex chromosome trisomy; SD: standard deviation.

Predictive role of babbling at 8 months on expressive vocabulary at 24 months

At 24 months, children with SCTs showed significantly lower expressive vocabulary development (U = 66.00; p = .001; η² = .32) than TD children. The mean number of words produced by children with SCTs was 77.67 (SD = 96.09; range = 0–316), whereas the mean number of words produced by TD children was 251.78 (SD = 199.32; range = 24–628).

To assess the predictive role of babbling on expressive vocabulary at 24 months, we examined the differences in children’s vocabulary size at 24 months between children in both groups who showed the ability to babble and children who did not produce babbling utterances at 8 months. Children (n = 21) who were able to babble had a significantly higher vocabulary size at 24 months (M = 210.43; SD = 193.94; range = 17–628) than children (n = 18) who did not show this competence (M = 96.89; SD = 127.57; range = 0–476) (U = 101; p = .01; η² = .16).

However, the two groups of children showed different patterns of correlation between measures at 8 months and language outcome at 24 months (see Table 5). In particular, in the TD group, we observed a significant correlation between canonical babbling at 8 months and expressive vocabulary at 24 months (Rho = .51; p < .05), whereas in the SCT group, no significant correlations were found between preverbal productions at 8 months and expressive vocabulary at 24 months. However, it should be noted that there was a nearly significant correlation between the production of variegated babbling at 8 months and vocabulary size at 24 months in children with SCTs (Rho = .41; p = .06). In both groups, expressive vocabulary at 24 months was not related to DQ at 8 months (in the SCT group: Rho = .20, p = .39; in the TD group: Rho = .34, p = .16), word comprehension at 8 months (in the SCT group: Rho = –.02, p = .93; in the TD group: Rho = .17, p = .52) or the frequency per minute of gazes (in the SCT group: Rho = .17, p = .47; in the TD group: Rho = –.20, p = .42).

Table 5.

Correlations between vocal productions (frequency per min) of children with SCTs and TD children at 8 months and their vocabulary size at 24 months.

	SCT (n = 21)			TD (n = 18)
	Rho	p	95% CI	Rho	p	95% CI
Total vocal productions	−.13	.58	−.53 to .32	.01	.98	−.46 to .48
Simple preverbal	−.33	.14	−.67 to .12	−.08	.74	−.53 to .40
Babbling	.26	.26	−.19 to .62	.21	.41	−.29 to .62
Canonical babbling	.26	.25	−.19 to .62	.51	.03	.06 to .79
Reduplicated babbling	.31	.18	−.14 to .65	.02	.93	−.45 to .48
Variegated babbling	.41	.06	−.03 to .72	−.14	.58	−.57 to .35

SCT: sex chromosome trisomy; TD: typically developing; CI: confidence interval.

Note. “p” is the significance value for bold values.

Discussion

Children with SCTs often show a delayed language development compared to children with TD (e.g. Bishop et al., 2019), but little is known about their first stage of communicative development. For these reasons, the present study aimed to describe the spontaneous preverbal skills of 8-month-old children with SCTs (XXY, XYY and XXX), analysing their word comprehension, vocal production and the use of gazes towards the communicative partner. In addition, the predictive role of preverbal vocal productions on later lexical development at 24 months was assessed.

The preverbal skills of these children were compared to those shown by TD children at the same chronological age. The two groups of children appeared significantly different in psychomotor development, with children with SCTs showing a mean DQ 12 points lower than that of TD children. However, it should be noted that all the participants had a DQ in the normal range. These data reflect those on IQ reported in the literature on older children with SCTs (Bishop & Scerif, 2011; Leggett et al., 2010).

Considering the children’s communicative stage, a significantly lower number of children with SCTs than TD children showed the ability to babble during the interaction session. Therefore, the children with SCTs appeared to lag behind their TD peers in reaching this stage. This result is particularly important, considering that late canonical babbling onset could be considered as a predictor of later developmental disabilities, such as problems in speech, language and reading (Oller et al., 1998).

Concerning the frequency of vocal productions, no significant differences were found between the two groups with respect to simple vocal productions (i.e. communicative grunts and vocalisations). In contrast, significant differences emerged in babbling, in particular, in the total production of babbling utterances and the frequency of production of canonical and reduplicated babbling. Considering only children who were able to produce babbling utterances, the phonetic features of babbling (types and number of different consonants) appeared to be similar between groups. The children with SCTs, thus, showed a pattern of delay in babbling emergency but no clear evidence of atypical characteristics. However, this result could not exclude the possibility of atypical phonetic development in children with SCTs, as this analysis was conducted only on the small proportion of children with SCTs that had already started to babble at 8 months of age and it refers only to the very first stages of consonant production in these children.

Even the significantly lower use of gazes addressed to the communicative partner by children with SCTs could be considered as an index of limited communication competence. This result should be investigated with particular attention in further studies to understand if the scarce use of gazes addressed to the partner could be considered as a communicative delay or as an interaction problem. This point is very important, considering the higher incidence of autism spectrum disorders found in children with SCTs (Bishop et al., 2011; Wilson et al., 2019).

The comparison among the subgroups of participants with SCTs showed that the preverbal skills of children with XXY, XYY and XXX are similar at 8 months of age. In fact, no significant differences were found among the subgroups in word comprehension, vocal production and gazes towards the partner. Although the small number of participants could influence these results, the similarity of the early communicative profiles of these children reflects the results of Bishop et al. (2019). These authors recently found that there are no consistent differences in the profiles of language problems in children with XXY, XYY and XXX. However, subgroups differences could emerge with larger samples or later in child development.

Finally, investigating the predictive role of preverbal vocal productions on later language development, the global frequency of utterances and the frequency of grunts and vocalisation did not seem to predict later vocabulary development in both groups of children. However, concerning babbling productions, a positive correlation between the frequency of canonical babbling and later lexical production was found in TD children but not in the SCT group. Only a nearly significant correlation between variegated babbling and later vocabulary size was found in children with SCTs. This result could be explained by the evidence that babbling was reported only in a limited number of children with SCTs (10 out of 26). In addition, the lexical outcome of TD children was more heterogeneous than that of the children with SCTs and the correlation coefficient values thus grew to be significant, despite the fairly small sample size (a similar interpretation was given by Stolt et al. (2014) to explain why they found different correlational patterns between their clinical and control group).

However, we should consider that the predictors of lexical outcomes could be different in populations with atypical language development. For instance, Mason-Apps et al. (2018) found that speech segmentation and initiating joint attention were the strongest predictors of later language in TD children, whereas non-verbal mental ability and responding to joint attention were the strongest predictors of later language in children with Down syndrome. In addition, Akhtar and Gernsbacher (2008) pointed out that the role of gaze in infant social cognition is not well established in atypically developing children. Future studies should assess whether babbling production could be a significant predictor of language development in children with SCTs later in development.

Limitations of the study, future directions and clinical implications

The principal limitation of the study is the small number of participants, which results in low statistical power, in particular to compare the children with different types of SCTs. However, the study has the value of considering a group of children at the same age, all identified on prenatal screening, which means it is relatively unbiased, compared to studies on cases identified during the course of investigations for developmental problems. To our knowledge, the present study is unique in analysing data on a homogeneous group of children with SCTs younger than 1 year.

The clinical importance of the study lies in the possibility of identifying early delays in the communication development of children with SCTs. The identification of possible risk factors at an early age could be very useful to prevent the appearance of possible language problems. Due to the limited abilities shown by children with SCTs in producing babbling and gazes addressed to the communicative partner, a possible intervention should be enhancing parental response to child preverbal productions. Studies on naturalistic language intervention mediated by parents showed that the parental response to babbling, for instance, by imitating the child, could be especially important to promote early children’s vocal development and their later linguistic skills (e.g. Scherer & Kaiser, 2007; Yoder & Warren, 2002).

Future studies should analyse children’s communicative productions later in development (e.g. at 12 or 14 months) to assess if early communicative skills (e.g. vocal and gestural production) could better predict their lexical outcomes at 24 months.

Footnotes

Acknowledgements

The authors would like to gratefully acknowledge the children and parents who participated in the study.

Author contribution statements

Laura Zampini: Conceptualization; Methodology; Formal Analysis; Investigation; Writing - Original Draft Preparation

Tiziana Burla: Formal Analysis; Writing - Original Draft Preparation

Gaia Silibello: Conceptualization; Investigation; Writing - Review & Editing

Elena Capelli: Formal Analysis; Writing - Original Draft Preparation

Francesca Dall’Ara: Conceptualization; Writing - Review & Editing

Claudia Rigamonti: Conceptualization; Writing - Review & Editing

Paola Francesca Ajmone: Conceptualization; Writing - Review & Editing

Federico Monti: Conceptualization; Writing - Review & Editing

Paola Zanchi: Conceptualization; Formal Analysis; Writing - Review & Editing

Faustina Lalatta: Conceptualization; Writing - Review & Editing

Maria Antonella Costantino: Conceptualization; Supervision; Writing - Review & Editing

Paola Giovanna Vizziello: Conceptualization; Investigation; Supervision; Writing - Review & Editing

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

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

ORCID iDs

Laura Zampini

Paola Zanchi

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