A missense variant in the SOX5 gene (c.221C > T) is associated with intellectual disability.

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The SOX5 gene has been identified as the pathogenic gene responsible for Lamb-Shaffer syndrome. In this study, we examined the SOX5 variant (c.221C > T, p.Thr74Met) within a Chinese family presenting with intellectual disability and evaluated the functional implications of SOX5 by in vitro experiment. The family underwent a clinical assessment of intellectual development, which included precise clinical exome sequencing to identify causative genetic variants. The potential deleterious effects and pathogenicity of the variant were predicted using bioinformatics tools such as Mutation Taster, PROVEAN, and SIFT. Additionally, protein stability was evaluated using I-Mutant, and 3D protein structures were modeled with I-TASSER. Western blots and QPCR were employed to assess gene expression and protein stability. Flow cytometry was utilized to compare the cell cycle dynamics between wild-type and mutant cells. A previously identified missense variant (c.221C > T) in the SOX5 gene was determined to be the underlying cause of intellectual disability in a Chinese family. Functional assays demonstrated that mutant cells exhibited increased levels of SOX5 mRNA and protein relative to wild-type cells, accompanied by enhanced protein stability. Additionally, the mutant SOX5 protein was found to alter the cell cycle and downregulate the mRNA expression levels of the ACAN, AXIN2, SOX9, and PDGFRA genes. We confirmed that the SOX5 p.Thr74Met variant is associated with intellectual disability in a second-generation Chinese family. This mutant protein potentially exhibits increased stability, influences the cell cycle, and downregulates genes related to bone and neural functions.