Functional analysis of heterozygous variants in the SALL1 gene in 2 children with Townes-Brocks syndrome with FSGS.

BACKGROUND: To investigate the functional characteristics of heterozygous variants in the SALL1 gene in two children with Townes-Brocks syndrome (TBS), as well as the underlying mechanisms leading to chronic kidney disease. METHODS: We retrospectively analyzed the clinical manifestations, laboratory findings, and genetic backgrounds of two TBS patients admitted to our hospital presenting with chronic kidney disease stage 2 and focal segmental glomerulosclerosis (FSGS). The genetic function was investigated through cultured cells transfected with variants. The Sall1 protein expression level was detected by western blotting. Immunofluorescence was also employed to detect the subcellular localization of SALL1. RESULTS: Novel heterozygous genetic variations (c.3175 C > T and c.694 C > T) were detected in two respective probands with distinct clinical presentations: Proband 1 presented with polydactyly, nephrotic syndrome, and stage 2 chronic kidney disease; while Proband 2 manifested renal dysplasia, progressive proteinuria, and also stage 2 chronic kidney disease. FSGS was confirmed by kidney biopsies from both probands. To assess the functional impact of these variations, we introduced mutant plasmids carrying the c.3175 C > T and c.694 C > T variants into podocytes. The expression level of variant c.3175 C > T(p.Q1059X) in podocytes showed a significant decrease compared to that of the wild-type (P < 0.05), whereas variant c.694 C > T(p.Q232X) was markedly upregulated (P < 0.01). Immunofluorescence analysis revealed aberrant localization patterns for both SALL1 variants within podocytes. CONCLUSIONS: Two patients with Townes-Brocks syndrome (TBS) harboring novel variants presented atypical phenotypes, characterized primarily by significant and rapidly progressing renal involvement. Rare renal biopsy pathology revealed the presence of focal segmental glomerulosclerosis (FSGS) in both cases. Experimental validation demonstrated that both variants led to alterations in the molecular size, expression level, and localization of the Sall1 protein, suggesting that these SALL1 gene variants might contribute to FSGS by impacting podocyte function.