NPHS1 and diabetic kidney disease: Although mature podocytes lack TJs and form SDs between opposing foot processes (FPs), several claudins (CLDNs), which are the TJ-specific integral membrane protein, such as CLDN3 in nephrin (NPHS1) knockout mice4 and CLDN1 in animals with diabetic nephropathy (DN)5, have been detected in podocytes of adult mouse kidneys.