Nail-patella syndrome.

The pathognomonic symptoms of patients with nail-patella syndrome are their small or absent patellae and dysplastic or absent finger- and toenails. Many of the patients suffer from renal symptoms which also affect their prognosis. In 1998, mutations in the gene encoding the transcription factor LMX1B were identified as underlying this autosomal-dominant disease. The LMX1B gene is expressed in a variety of tissues, and the symptoms are reflected nicely by its expression pattern. LMX1B is essential for dorso-ventral pattern formation in the limbs, for differentiation of the anterior portions of the eyes, for development of certain neuron populations in the central nervous system, and for the differentiation and maintenance of podocytes. Accordingly, kidney biopsies of patients with nail-patella syndrome show an altered podocyte structure and defects in the glomerular basement membrane. Recent evidence suggests that LMX1B regulates genes which encode proteins associated with the actin cytoskeleton.