Childhood and adolescence disorders A family based association study of neuronal nitric oxide synthase gene polymorphism in autism spectrum disorders

Objective: Autism is a neurodevelopmental disorder characterized by impairments and abnormalities in verbal and non-verbal communication and socialization alongside with restricted-stereotyped interests and behaviors. Several factors have been implicated in the etiology of autism, including genetic, environmental and autoimmune factors however the underlying etiology of autism is unknown. Nitric oxide (NO), is generated from L-arginine by the enzyme nitric oxide synthase (NOS), is an important signaling molecule that affects neurodevelopmental processes in the central nervous system. It has been implicated in the development of certain psychiatric disorders, including autism spectrum disorders. In addition, NO is a free oxygen radical that plays a key role in immune-mediated neurotoxicity via mitochondrial inhibition. The aim of this study is to investigate neuronal nitric oxide synthase (NNOS) gene polymorphism in autism spectrum disorders (ASD).

Method: Subjects in this study were children and adolescents aged 2-18 years old who were referred and followed up with diagnosis of DSM-IV ASD in Istanbul Medical Faculty, Child and Adolescent Psychiatry Department. Childhood Autism Rating Scale (CARS) was used to assess the severity of autism symptoms. Ten cc blood sample of affected child and biological mother and father trios were taken to sterile EDTA test tube for DNA isolation. Polimerase chain reaction (PCR), restriction fragment length polymorphism (RFLP) and agars gel electrophoresis are used to assess neuronal nitric oxide synthase (NNOS) gene polymorphism in DNA samples. Genetic analysis was conducted in Istanbul University, Institute of Experimental Medicine (DETAE), Molecular Medicine Department. Family based approaches like transmission disequilibrium test (TDT) and haplotype-relative-risk (HRR) were used in data analysis. Correlation between inherited alleles and quantitative analysis like CARS score, IQ score, age of mother was assessed using ANOVA.

Results: 101 subjects (16 girls, 15,8%; 85 boys, 84,4%) with diagnosis of ASD and their biological parents, a total of 303 subjects, were included in the study. We found significant association between NNOS 276 gene and autism spectrum disorders (p:0,0077) (X2:5.846). There is no significant association between NNOS 84 gene and autism spectrum disorders. Also there is no correlation between inherited alleles and quantitative analysis like CARS score, IQ score, age of mother according to ANOVA.

Conclusion: The findings of this study suggest that NNOS might appear to be a viable candidate gene for the pathogenesis of autism and have a role in development of ASD phenotype. Further genetic and molecular studies are needed on this area.