Onychoosteodysplasia, Turner-Kieser syndrome
Nail patella syndrome is a hereditary osteo-onychodysplasia. Incidence at birth is estimated at 1/45 000 and prevalence at 1/50 000. The disease has been reported in patients worldwide. In addition to nail dysplasia with triangular lunula, patients can present with hypoplastic or absent patellas, iliac exostoses (`iliac horns') and dysplastic elbows. Ocular involvement is observed in approximately one third of patients (glaucoma, ocular hypertension etc.) and sensorineural hearing loss can be present. Nephropathy is observed in 1/3 to half of the cases. It leads to proteinuria, in some cases associated with nephrotic syndrome, hematuria and arterial hypertension. Characteristic modifications of the glomerular basement membrane can be observed by electron microscopy. The disease is transmitted as an autosomal dominant trait and results from mutations in the LMX1B gene. This gene encodes a transcription factor belonging to the LIM homeodomain protein family, which plays an important role during the development of the limbs, kidneys and eyes. There may be two allelic gene mutations, one responsible for nail-patella syndrome without nephropathy and one for the syndrome with nephropathy. Treatment is symptomatic. In case of nephropathy, it aims mainly at reducing the proteinuria in order to slow the progression to renal failure (observed in 1/3 of patients around the age of 30).