While TTC21B had been initially recognized as a potential genetic cause of NPHP (OMIM 613820), and short-rib thoracic dysplasia 4 with or without polydactyly it has also been reported as a possible genetic cause of glomerular compartment defects, in addition to tubulointerstitial alterations, manifesting FSGS [154–156]. This evidence concerns the gene TTC21B and focal segmental glomerulosclerosis.