These findings provided the impetus to further examine the importance of GAK. To determine if GAK transcript reduction was associated with reduced GAK protein expression in patients with CKD, we performed immunofluorescence on human focal segmental glomerulosclerosis (FSGS) biopsies costained for GAK and the podocyte-specific marker nephrin. The gene discussed is NPHS1; the disease is focal segmental glomerulosclerosis.