Genetic analysis of focal segmental glomerulosclerosis in Thailand

Background: The genetic variants spectra of focal segmental glomerulosclerosis (FSGS) vary among different populations. Here we described the clinical and genetic characteristics of biopsy-proven FSGS patients in Thailand. We also used special staining in renal biopsy tissue to describe protein expression related to the variants found by whole-exome sequencing (WES). Also, a functional study in cells was studied to investigate the etiologic evidence of the variants found by WES. Methods: Fifty-three unrelated FSGS patients without secondary causes were included in our study. Whole-exome sequencing (WES) was subsequently performed. Immunohistochemistry (IHC) staining method was used to characterize the morphology of renal pathology for clinical and genomic correlation. Cell-based split-luciferase-based trimer formation assay was used to investigate whether the variances found by WES related to clinical, pathology, and genomic findings. Results: Of 53 FSGS patients, 35 patients were adults (66.0%), and 51 patients were sporadic cases (96.2%). Clinical diagnosis before kidney biopsy was steroid-resistant nephrotic syndrome (SRNS) in 58.5%, and proteinuric chronic kidney disease in 32.1%. Using WES, disease-associated pathogenic/likely pathogenic (P/LP) variants could be identified in six patients including the two familial cases, making the P/LP detection rate of 11.3% (6/53). Of these six patients, two patients harbored novel variants with one in the COL4A4 gene and one in the MAFB gene. Four other patients carried previously reported variants in the CLCN5, LMX1B and COL4A4 genes. Protein expression study with IHC staining of α5(IV) collagen in kidney tissues were positive in kidney tissues of both P/LP variants and benign variants; therefore, IHC staining did not correlated with pathogenicity of variants classified. However, cell-based split-luciferase-based trimer formation assay of α345(IV) collagen showed decreased in protein expression of α345(IV) collagen in the cells with P/LP variants; hence, predicted that these P/LP variants were the cause of FSGS in the respective patients.  Conclusions: The overall P/LP variant detection rate by WES in biopsy-proven FSGS patients was 11.3%. The most identified variants were in COL4A4. IHC staining of α5(IV) collagen was not associated with pathogenicity of variants, but cell-based study can successfully demonstrated the etiologic evidence of COL4A4 variants found by WES.