Whole exome sequencing reveals a mutation in ARMC9 as a cause of mental retardation, ptosis, and polydactyly

Intellectual disability (ID) refers to deficits in mental abilities, social behaviour and motor skills to perform activities of daily living as compared to peers. Numerous genetic and environmental factors may be responsible for ID. We report on identification of a novel gene for syndromic ID, using homozygosity mapping followed by exome sequencing in a family with mental retardation, ptosis and polydactyly. The analysis revealed a synonymous mutation c.879G>A which leads to a splicing defect in ARMC9 gene. The variant is present in conserved region of ARM domain of ARMC9 protein which is predicted to form a platform for protein interaction. This domain is likely to be altered in patients due to splicing defect caused by this synonymous mutation. Our study was helpful in elucidation of molecular basis of mental retardation, ptosis and polydactyly phenotype and addition of ARMC9 to group of genes leading to syndromic ID.