A Strong Candidate Gene for Nonsyndromic Intellectual Disability Phenotype: SGSM3.

SGSM proteins are small modulator proteins interacting with proteins in the RAS signaling pathway. Studies with mouse and human tissues indicated that SGSM genes were highly expressed in the brain and could be expressed at different levels at different stages of development in fetal and adult brain tissue. It was first reported by Birnbaum et al. that the SGSM3 gene might be associated with a Mendelian inherited disease in families of Ashkenazi Jews with clinical manifestations of intellectual disability (ID). In this study, a novel homozygous stop-gain (NM_015705.6: c.1576C>T: p.(Arg526Ter)) variation was detected in the SGSM3 gene in two siblings with short stature and ID findings. The report of two cases with bi-allelic LOF variants in the SGSM3 gene from different populations with similar clinical manifestations strengthens the potential of this gene as a candidate gene for the nonsyndromic ID phenotype. Functional studies are required to investigate the signaling pathways affected by SGSM3 gene variations to produce the ID phenotype and their effect on the functioning of neurons.