Abstract
Autism spectrum disorder (ASD) is a complex disorder with a heterogeneous etiology. Fragile X syndrome (FXS) is recognized as the most common single gene mutation associated with ASD. FXS patients show some autistic behaviors and may be difficult to distinguish at a young age from autistic children. However, there have been no published reports on the prevalence of FXS in ASD patients in Thailand. In this study, we present a pilot study to analyze the CGG repeat sizes of the FMR1 gene in Thai autistic patients. We screened 202 unrelated Thai patients (168 males and 34 females) with nonsyndromic ASD and 212 normal controls using standard FXS molecular diagnosis techniques. The distributions of FMR1 CGG repeat sizes in the ASD and normal control groups were similar, with the two most common alleles having 29 and 30 CGG repeats, followed by an allele with 36 CGG repeats. No FMR1 full mutations or premutations were found in either ASD individuals or the normal controls. Interestingly, three ASD male patients with high normal CGG and intermediate CGG repeats (44, 46, and 53 CGG repeats) were identified, indicating that the prevalence of FMR1 intermediate alleles in Thai ASD patients was approximately 1% while these alleles were absent in the normal male controls. Our study indicates that CGG repeat expansions of the FMR1 gene may not be a common genetic cause of nonsyndromic ASD in Thai patients. However, further studies for mutations other than the CGG expansion in the FMR1 gene are required to get a better information on FXS prevalence in Thai ASD patients.
Highlights
Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by deficits in social interactions and social communications, as well as restricted interests and stereotyped and repetitive behaviors
All normal controls had fragile X mental retardation 1 gene (FMR1) CGG repeats in the normal range of less than or equal to 41 repeats
This study reports for the first time the frequency of the Fragile X syndrome (FXS) mutation in ASD patients in Thailand
Summary
Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by deficits in social interactions and social communications, as well as restricted interests and stereotyped and repetitive behaviors. The prevalence of ASD was estimated to be 1 in 54 children in a recent study, with a 4 : 1 ratio of affected males to females [1]. About 10-20% of ASD cases have been identified as having a genetic disorder caused by chromosomal aberrations and single gene mutations, including fragile X syndrome, tuberous sclerosis, and Rett syndrome. More than 100 ASD-risk genes carrying mutations have been identified in ASD [3,4,5,6,7,8]; genetic testing is indicated in the medical workup for individuals with ASD, which may include G-banded karyotyping, fragile X testing, chromosomal microarray, and/or whole exome sequencing [5, 9]
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