The SORCS3 gene is mutated in brothers with infantile spasms and intellectual disability.

The sortilin-related VPS10 domain-containing receptor 3 (SORCS3) is a type-I receptor transmembrane protein and a member of the vacuolar protein sorting 10 receptor family. Proteins of this family are defined to have a vacuolar protein sorting 10 domain at the N-terminus. They play important roles as a sorting agency within the cells and transport a variety of intracellular proteins between the Golgi apparatus, endosome, lysosome, secretory granules, and plasma membrane. They are also involved in signal transduction. Clinically, they have been implicated in the pathophysiology of multiple sclerosis and Alzheimer's disease. Here, we report details on two brothers deceased at 20 months and 2 years of age, respectively, with a neurological phenotype including infantile spasms, intellectual disability, global developmental delay, microcephaly, hypotonia, spastic quadriplegia, and delayed myelination. Whole exome sequencing and autozygome analysis showed homozygous missense variant in the SORCS3 gene. The pathogenicity is supported by functional studies in the patient mesenchymal stem cells. Patients' cells showed less proliferation capability than normal cells. In addition, making the same mutation in normal cells revealed a viability defect in them. This is the first study on human subjects with a SORCS3 gene defect and supports the important role of SORCS3 in the central nervous system.