Too long have I seen the “Nail-Patella Syndrome” included in the differential diagnosis of renal disease without understanding anything about it…that ends today!
The Nail Patella Syndrome (NPS), also referred to as Hereditary Onychoosteodysplasia, is an autosomal dominant inherited disorder which is caused by mutations in LMX1B, which encodes a transcription factor important in the development of the limb, eye, and kidneys. Although it most commonly results in nailbed deformities such as the one depicted and also dysplasia of the patellae or other bones, in about 1/3 of cases it can result in a nephropathy.
The nephropathy of Nail-Patella Syndrome typically presents with either hematuria, proteinuria, or both. Both frank nephrotic syndrome and progression to ESRD are possibilities, though occur in a minority of patients. Biopsy shows fibrosis, and the presence of collagen fibrils which cause GBM thickening. It can probably be classified as a “podocytopathy” in the sense that knockout mice lacking the LMX1B gene show a deficit in podocyte development. The current thought is that patients with mutations which are more severe are the ones most likely to develop kidney disease.