Novel variants underlying autosomal recessive neurodevelopmental disorders with intellectual disability in Iranian...

Intellectual disability (ID) is a heterogeneous group of neurodevelopmental disorders that is characterized by significant impairment in intellectual and adaptive functioning with onset during the developmental period. Whole-exome sequencing (WES)-based studies in the consanguineous families with individuals affected with ID have shown a high burden of relevant variants. So far, over 700 genes have been reported in syndromic and non-syndromic ID. However, genetic causes in more than 50% of ID patients still remain unclear.

Whole-exome sequencing was applied for investigation of various variants of ID, then Sanger sequencing and in silico analysis in ten patients from five Iranian consanguineous families diagnosed with autosomal recessive neurodevelopmental disorders, intellectual disability, performed for confirming the causative mutation within the probands. The most patients presented moderate-to-severe intellectual disability, developmental delay, seizure, speech problem, high level of lactate, and onset before 10 years.

Filtering the data identified by WES, two novel homozygous missense variants in FBXO31 and TIMM50 genes and one previously reported mutation in the CEP290 gene in the probands were found. Sanger sequencing confirmed the homozygote variant's presence of TIMM50 and FBXO31 genes in six patients and two affected siblings in their respective families. Our computational results predicted that the variants are located in the conserved regions across different species and have the impacts on the protein stability.

Hence, we provide evidence for the pathogenicity of two novel variants in the patients which will expand our knowledge about potential mutation involved in the heterogeneous disease.