Nail-patella syndrome and renal involvement. Description of three cases and literature review.

Nail-patella syndrome (NPS) is a rare, autosomal dominant disorder reported in approximatively 1/50,000 individuals. It is characterized by hypoplastic or absent patellae, dystrophic nails, dysplasia of the elbows and iliac horns. Less frequently renal and ocular damages occur. The abnormal gene in NPS is located at the distal end of the long arm of Chromosome 9. Mutations in the human LMX1B gene have been demonstrated to be responsible for NPS. It encodes a LIM-homeodomain transcription factor which plays an important role in limb development in vertebrates. Extensive mutation analysis of different NPS families by different groups failed to demonstrate any genotype-phenotype correlation. Renal involvement occurs in 30-60% of patients and presents with proteinuria and/or microscopic hematuria, edema, hypertension. Progression to nephrotic syndrome occurs in less than 20% of patients, and renal failure in about 10% of NPS patients requiring dialysis and/or transplantation. We report three cases of NPS with different degrees of renal involvement and present a review of the literature on this rare hereditary condition.