Autism spectrum disorder (ASD) is a neurodevelopmental disorders(NDDs) characterized by differences in social communication and the presence of repetitive behaviors or restrictive interests(1). According to the latest prevalence estimate from the Centers for Disease Control and Prevention (CDC) in the United States, approximately 1 in 36 children aged 8 have been identified with ASD(2). Such a high prevalence has drawn increasing attention to children with autism. In addition, studies on gender differences in ASD have indicated that ASD is more common in boys than in girls, with a ratio of approximately 3:1(3). Attention deficit hyperactivity disorder (ADHD) is characterized by significant levels of inattention, disorganization and/or hyperactivity-impulsivity(4), and is associated with a decline in quality of life (5) and impaired social cognitive ability(6). ADHD is more common in boys than girls by a ratio of about 2:1(4). Specific learning disorder (SLD) is a group of NDDs characterized by developing and applying specific learning skills, such as listening, speaking, reading, writing, memory, reasoning, and computation(4). SLD is more common in school-age children with a global incidence of about 5%-15%(4, 7). Furthermore, SLD could significantly affect children's school adaptation and academic performance, such as forward and backward digit memory damage, and difficulties can worsen with age (8). Similar to ASD and ADHD, SLD is also more common in boys than in girls, with a ratio of about 2–3:1(4). Children with SLD often suffer from various psychiatric comorbidities, with ADHD being the most common(9). Although ADHD and SLD differ in diagnosis, some studies have confirmed the co-occurrence of both (ADHD + SLD)(10, 11), with about 28%-45% of children with ADHD also displaying SLD symptoms(12, 13). Due to significant gender differences in the incidence of NDDs and variations in incidence at different ages, it is important to consider the need to include gender and age factors in the analysis and further explore these differences.
ASD, ADHD, SLD, or ADHD + SLD can have a great impact on every child and family. Children with these NDDs exhibit deficits in intellectual functioning and adaptive behavior, necessitating targeted interventions to facilitate their integration into society(14–16). To facilitate effective interventions and support, clinical assessments, such as the Wechsler Intelligence Scale for Children-Fourth edition (WISC-Ⅳ) and Adaptive Behavior Assessment System-Second Edition (ABAS-Ⅱ) are commonly utilized to identify the cognitive and adaptive deficits of these children. These assessments can help tailor interventions to address individual needs and improve the child's integration into school and society. It may be important to identify a specific structure of intelligence that is typical of these children, and to better understand the characteristics of intelligence in these children that may lead to new theoretical and clinical insights.
The WISC-Ⅳassesses children's intelligence through five composite scores: Full-scale Intelligence Quotient (FSIQ), Verbal Comprehension Index (VCI), Perceptual Reasoning Index (PRI), Working Memory Index (WMI) and Processing Speed Index (PSI). Research has demonstrated that children with ASD exhibit significantly lower FSIQ compared to neurotypical children(17, 18). In comparison to other NDDs, children with ASD displayed higher FSIQ, VCI, and PRI scores than those with ADHD or SLD, with ASD children also exhibiting higher WMI scores than SLD children (19). Conversely, SLD children had higher FSIQ and WMI scores than ADHD children(20), while their VCI and PRI scores were higher than those of ADHD children(21). Recent research conducted in China reported that ADHD + SLD children had lower FSIQ, VCI, and PRI scores than ADHD children(10). However, Evinc SG reported that WISC composite scores did not significantly differ between children with ADHD and those with other psychiatric diagnoses(22). The inconsistent results of these studies suggest the need for further research with larger sample sizes.
Apart from IQ, children’s adaptive behavior is a crucial aspect of intellectual and developmental disabilities in these four disorders(16, 23–25). In order to provide more accurate rehabilitation training, WISC and ABAS are often used together to assess children(26, 27). Recently, IQ and adaptive behavior have been increasingly used together in the diagnosis of NDDs(28, 29). Assessing a child's IQ can be helpful in aiding clinicians to diagnose specific disorders, and comprehend the child's cognitive strengths and weaknesses, thereby enabling physicians to develop more effective interventions(30). Whereas adaptive behavior assessments can provide valuable information in making diagnostic decisions, such as identifying social skills impairments in children with ASD. ABAS-Ⅱ is a widely used standardized tool to assess adaptive behaviors in children with ASD, ADHD, and other disorders(16, 23). It has been suggested that ABAS may be a useful adjunctive diagnostic tool to obtain useful information on the relationship between ASD symptoms and IQ in clinical and research settings(31, 32). However, most of the studies exploring the relationship between IQ and adaptive behavior in these four disorders have small sample sizes. Therefore, large sample studies are urgently needed to examine the age and gender differences in IQ and adaptive behavior of children with these disorders. Additionally, few studies have analyzed both the WISC-Ⅳ and ABAS-Ⅱ simultaneously for these disorders, indicating the need for more comprehensive research.
Although some previous studies have investigated gender and age differences in the prevalence of these four disorders(3, 4), findings regarding gender and age differences in the performance of the WISC-Ⅳ among these four disorders have been inconsistent. For example, among children with ASD, girls had higher scores in VCI, WMI, and PSI than boys (33); In ADHD children, boys' VCI, PRI, and FSIQ scores were higher than girls’ (34); Among SLD children, boys showed more spelling deficits than girls, while more girls were impaired in arithmetic(35). Moreover, among neurotypical children in rural China, boys’ FSIQ score was 0.97 points higher than girls’, boys’ VCI and PRI scores were 2.44 points and 3.68 points higher than girls’, and girls’ WMI and PSI scores were 1.32 points and 3.10 points higher than boys’, respectively(36). Therefore, there is a lack of comprehensive analysis of gender differences in these four disorders. In addition, cognitive impairment changes with age in children with NDDs(37), but the research results on age differences in intelligence of children with NDDs are also inconsistent. For instance, a study has shown significant differences in PSI scores between children aged 6–9 and 10–16(38), while another study in Chinese children with ADHD also found significant differences in VCI and FSIQ scores among three age groups (6–8, 9–11 and 12–14 years old)(39). Nonetheless, a study on general children found no significant differences in WISC composite scores among five age groups (6–7, 8–9, 10–11, 12–13, and 14–16 years old) (40). Thus, there is no consensus on age differences in intelligence among children with NDDs. Although some studies have found significant differences in WISC composite scores among certain age groups, no research has been conducted on gender and age differences in intelligence among school-age children with these four disorders. Therefore, there is a need for detailed analysis and study of gender and age differences in these disorders to develop gender-specific and age-specific interventions.
To sum up, the aims of the current study were as follows: First, we analyzed the intellectual structure and adaptive behavior of four disorders in school-age children (ASD, ADHD, SLD, and ADHD + SLD) and made detailed comparisons, showing the strengths and weaknesses of each disorder. Second, we examined whether there were gender and age differences in the performance of intelligence structure in these disorders.