Nail-patella syndrome (NPS) is an inherited developmental disorder most commonly involving maldevelopment of the fingernails, kneecaps and elbow joints. NPS exhibits wide variation in phenotypic expression within and among families with respect to these features. Other skeletal abnormalities such as hip dislocation and club foot have also been reported in some individuals with NPS. There is an association between NPS and renal disease, and between NPS and open-angle glaucoma (OAG), but it is not known whether mutations in a single gene cause the observed skeletal, renal and ophthalmic abnormalities. Recently, LMX1B , a transcription factor of the LIM-homeodomain type with homologs that are important for limb development in vertebrates, was mapped to the same general location as NPS at 9q34. We sequenced a large segment of LMX1B from the genomic DNA of probands from four families with NPS and OAG, and identified four mutations: two stop codons, a deletion causing a frameshift and a missense mutation in a functionally important residue. The presence of these putative loss-of-function mutations in the DNA of individuals with NPS indicates that haploinsufficiency of LMX1B underlies this disorder. These findings help to explain the high degree of variability in the NPS phenotype, and suggest that the skeletal defects in NPS are a result of the diminished dorsoventral patterning activity of LMX1B protein during limb development. The results further suggest that the NPS and OAG phenotypes in the families studied result from mutations in a single gene, LMX1B.

Nail-patella syndrome (NPS), a pleiotropic disorder exhibiting autosomal dominant inheritance, has been studied for >100 years. Recent evidence shows that NPS is the result of mutations in the LIM-homeodomain gene LMX1B. To determine whether specific LMX1B mutations are associated with different aspects of the NPS phenotype, we screened a cohort of 41 NPS families for LMX1B mutations. A total of 25 mutations were identified in 37 families. The nature of the mutations supports the hypothesis that NPS is the result of haploinsufficiency for LMX1B. There was no evidence of correlation between aspects of the NPS phenotype and specific mutations.

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Study Design Statistical analysis of genomic screening and fine mapping data. Objective The goals of this study were to analyze a region on chromosome 17 and to identify specific genetic determinants within this region linked to familial idiopathic scoliosis (FIS) in a subgroup of families in which affected males have undergone surgery. Summary of Background Data The high prevalence and variability of FIS is indicative of genetic heterogeneity. To localize genes related to scoliosis, identification of groups of families with common clinical characteristics is a strategy that reduces genetic heterogeneity. Two independent studies have implicated a region on chromosome 17 as related to FIS. Methods With approval of the Institutional Review Board, the initial study population consisted of 202 families (1198 individuals), each of which had 2 or more affected individuals; 17 of those families had an affected male who had surgery. Individuals underwent genomic screening and subsequent fine mapping. Results were obtained using model-independent linkage analysis, with scoliosis set as a qualitative and as a quantitative trait, as implemented in SIBPAL (S.A.G.E., v4.5). The level of significance was set at P ≤ 0.05. Results The initial study population had significant results at markers d17s975 and d17s2196. Analyses of a subgroup of families with males having undergone surgery using a customized single nucleotide polymorphism panel resulted in increased significance of this region. Conclusion The data confirm a previously reported genetic locus on chromosome 17 as statistically significant in the etiology of FIS within a subgroup of families in which an affected male had spinal surgery.

Nail patella syndrome (NPS) has been shown to result from loss of function mutations within the transcription factor LMX1B. In a large NPS family a 17bp intronic deletion encompassing a consensus branchpoint sequence was observed to segregate with the NPS phenotype. RNA analysis demonstrated that deletion of the branchpoint sequence resulted in skipping of the downstream exon. A mechanism to explain this phenomenon is presented.

The relationship of delayed membranous cranial ossification to cranium bifidum and parietal foramina syndromes is unclear. We report on a family with delayed cranial membranous ossification (OMIM 155980) that segregates with an apparently balanced reciprocal translocation between chromosomes 2 and 3. The propositus had apparently low-set ears, proptosis, and a soft skull at birth. A radiographic survey of the skeleton showed markedly decreased ossification of the cranial bones and no other skeletal abnormalities. The mother and maternal grandmother of the propositus have brachycephaly, hypertelorism, and a history of a soft skull at birth. Chromosome analysis of peripheral blood from the propositus showed 46,XY,t(2;3)(p15;q12). The propositus, mother, and grandmother carry the same reciprocal translocation, whereas the mother's two phenotypically normal sibs have a normal karyotype. We used an STS-linked BAC resource to define the translocation breakpoint by identifying flanking BAC clones from both chromosomes 2, 1006D24 (D2S2279) and 1060A5 (D2S2231), and chromosome 3, 3D17 (WI8558) and 3D18 [CITB Human BAC Library, J.R.K.]. This represents the second report of a family with delayed membranous ossification of the cranium and the first report of the phenotype segregating with a chromosome rearrangement.

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