Abstract
Genetic focal segmental glomerulosclerosis (FSGS) is an important but underestimated cause of inherited proteinuric chronic kidney disease (CKD) in adults. We discuss a case of familial CKD due to inverted formin 2 (INF2) gene mutation, where three siblings had disparate phenotypic presentations ranging from CKD with subnephrotic proteinuria to nephrotic-range proteinuria with collapsing FSGS on kidney biopsy over a period of 8 years. The youngest sibling was the index case. The family agreed to undergo genetic testing only after two more siblings were diagnosed with kidney disease. This case highlights how clinical heterogeneity, absence of family history in the index case, initial lack of specific biopsy-proven diagnosis and reluctance to undergo genetic testing can delay the diagnosis of genetic kidney disease in adults.