Abstract
Nail–patella syndrome is an autosomal-dominant hereditary disease named for dysplastic fingernails and toenails and hypoplastic or absent kneecaps evident in patients with the syndrome. Prognosis is determined by the nephropathy that develops in many such patients. Besides podocyte foot-process effacement, pathognomonic changes in the kidney comprise electron-lucent areas and fibrillar inclusions in the glomerular basement membrane. These characteristic symptoms are caused by mutations in the gene encoding the transcription factor LMX1B, a member of the LIM-homeodomain gene family. Comparable with the human syndrome, homozygous Lmx1b knockout mice lack patellae and suffer from severe podocyte damage. In contrast, however, podocin and the α3 and α4 chains of collagen IV are absent in the glomeruli of Lmx1b knockout mice. Further studies with podocyte-specific Lmx1b knockout mice have confirmed the importance of LMX1B in podocytes, as these mice apparently develop foot processes initially but lose them later on. We therefore conclude that LMX1B is essential for the development of metanephric precursor cells into podocytes and possibly also for maintaining the differentiation status of podocytes. LMX1B can serve as a model system to elucidate a genetic program in podocytes.
Highlights
Nail–patella syndrome is an autosomal-dominant hereditary disease named for dysplastic fingernails and toenails and hypoplastic or absent kneecaps evident in patients with the syndrome
Nephrin and podocin participate in the formation of the slit diaphragm complex, α-actinin-4 crosslinks actin filaments in podocytes, and TRPC6 belongs to a special class of cation channels
In 1998, were the first mutations in the LMX1B gene published for patients suffering from nail–patella syndrome [12,13,14], but a report appeared on the first characterisation of the Lmx1b knock-out mouse [25]
Summary
Nail–patella syndrome is an autosomal-dominant hereditary disease named for dysplastic fingernails and toenails and hypoplastic or absent kneecaps evident in patients with the syndrome. Since several other genes have been cloned that when mutated lead to glomerular disease and which in the kidney are (almost) expressed in podocytes.
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