The genetic landscape of autism spectrum disorder in the Middle Eastern population.

Introduction: Autism spectrum disorder (ASD) is characterized by aberrations in social interaction and communication associated with repetitive behaviors and interests, with strong clinical heterogeneity. Genetic factors play an important role in ASD, but about 75% of ASD cases have an undetermined genetic risk. Methods: We extensively investigated an ASD cohort made of 102 families from the Middle Eastern population of Qatar. First, we investigated the copy number variations (CNV) contribution using genome-wide SNP arrays. Next, we employed Next Generation Sequencing (NGS) to identify de novo or inherited variants contributing to the ASD etiology and its associated comorbid conditions in families with complete trios (affected child and the parents). Results: Our analysis revealed 16 CNV regions located in genomic regions implicated in ASD. The analysis of the 88 ASD cases identified 41 genes in 39 ASD subjects with de novo (n = 24) or inherited variants (n = 22). We identified three novel de novo variants in new candidate genes for ASD (DTX4, ARMC6, and B3GNT3). Also, we have identified 15 de novo variants in genes that were previously implicated in ASD or related neurodevelopmental disorders (PHF21A, WASF1, TCF20, DEAF1, MED13, CREBBP, KDM6B, SMURF1, ADNP, CACNA1G, MYT1L, KIF13B, GRIA2, CHM, and KCNK9). Additionally, we defined eight novel recessive variants (RYR2, DNAH3, TSPYL2, UPF3B KDM5C, LYST, and WNK3), four of which were X-linked. Conclusion: Despite the ASD multifactorial etiology that hinders ASD genetic risk discovery, the number of identified novel or known putative ASD genetic variants was appreciable. Nevertheless, this study represents the first comprehensive characterization of ASD genetic risk in Qatar's Middle Eastern population.

A Novel Missense Mutation in SRD5A3 Causes Congenital Disorder of Glycosylation Type I (Cerebello-Ocular Syndrome)

Abstract A consanguineous Qatari family having an autosomal recessive disorder characterized by severe mental retardation, cerebellar vermis hypoplasia, retinal degeneration, optic nerve atrophy, ataxic gait, and seizures was studied for identification of the offending gene and mutation. Homozygosity mapping identified an 11.4 Mb critical interval at 4q12 to q13.2 that would contain the gene responsible for the disorder. Ten positional candidate genes were screened for pathogenic mutations, but none were identified. Next-generation exome sequencing in one affected individual identified a novel SRD5A3 missense mutation c.T744G/p.F248L, which was subsequently confirmed by Sanger sequencing, suggesting a congenital disorder of glycosylation type IQ defect. Isoelectric focusing of serum transferrin showed a type I pattern indicative of an .-glycan assembly defect. This is a novel pathogenic mutation and the first SRD5A3 missense mutation as all others are protein-truncating mutations.