[Functional validation of a rare SOS1 gene variant and literature review]

To analyze the functional impact of a rare heterozygous variant of SOS1 gene (c.283G>A, p.E95K) identified in a fetus with cervical cystic hygroma and to explore its association with the disease phenotype.

A pedigree analysis was carried out to evaluate the co-segregation of the variant with the disease phenotype. Bioinformatic tools were employed to assess the conservation, protein structure and stability. Functional validation was conducted on HEK293T cells using fluorescence quantitative reverse transcription-PCR and Western blotting to measure the expression of SOS1 and phosphorylation levels of extracellular regulated protein kinases (ERK) and c-Jun N-terminal kinase. A literature review of previously reported disease-associated SOS1 variants was also carried out. This study has been approved by the Medical Ethics Committee of West China Second University Hospital, Sichuan University (Ethics No.: 201940).

The variant was inherited from the husband of the woman with distinctive facial features and has co-segregated with the phenotype. Bioinformatics analysis indicated that the variant is located in a highly conserved region, and that p.E95K could disrupt key amino acid interactions and protein stability. Multiple bioinformatic predictions consistently suggested the pathogenicity of this variant. Functional assays demonstrated reduced SOS1 protein expression and decreased ERK phosphorylation.

This study has revealed the functional impact of the SOS1 c.283G>A (p.E95K) variant, suggesting that it may contribute to the developmental phenotypes through a haploinsufficiency mechanism.