Atypical focal segmental glomerulosclerosis associated with a new PODXL nonsense variant.

Podocalyxin (PODXL) is a highly sialylated adhesion glycoprotein that plays an important role in podocyte's physiology. Recently, missense and nonsense dominant variants in the PODXL gene have been associated with focal segmental glomerulosclerosis (FSGS), a leading cause of nephrotic syndrome and kidney failure. Their histologic description, however, was superficial or absent. We performed exome sequencing on a three-generation family affected by an atypical glomerular nephropathy and characterized the disease by light and electron microscopy. The disease was characterized by FSGS features and glomerular basement membrane duplication. Six family members displayed chronic proteinuria, ranging from mild manifestations without renal failure, to severe forms with end-stage renal disease. Exome sequencing of affected twin sisters, their affected mother, healthy father, and healthy maternal uncle revealed a new nonsense variant cosegregating with the disease (c.1453C>T, NM_001018111) in the PODXL gene, which is known to be expressed in the kidney and to cause nephropathy when mutated. The variant is predicted to lead to a premature stop codon (p.Q485*) that results in the loss of the intracytoplasmic tail of the protein. This is the first description of a peculiar association combining a PODXL stop-gain variant and both FSGS and membranoproliferative glomerulonephritis features, described by light and electron microscopy.