Heterozygous mutations in BBS1, BBS2 and BBS6 have a potential epistatic effect on Bardet-Biedl patients with two mutations at a second BBS locus.
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Bardet-Biedl syndrome (BBS) is a pleiotropic genetic disorder with substantial inter- and intrafamilial variability, that also exhibits remarkable genetic heterogeneity, with seven mapped BBS loci in the human genome. Recent data have demonstrated that BBS may be inherited either as a simple Mendelian recessive or as an oligogenic trait, since mutations at two loci are sometimes required for pathogenesis. This observation suggests that genetic interactions between the different BBS loci may modulate the phenotype, thus contributing to the clinical variability of BBS. We present three families with two mutations in either BBS1 or BBS2, in which some but not all patients carry a third mutation in BBS1, BBS2 or the putative chaperonin BBS6. In each example, the presence of three mutant alleles correlates with a more severe phenotype. For one of the missense alleles, we also demonstrate that the introduction of the mutation in mammalian cells causes a dramatic mislocalization of the protein compared with the wild-type. These data suggest that triallelic mutations are not always necessary for disease manifestation, but might potentiate a phenotype that is caused by two recessive mutations at an independent locus, thus introducing an additional layer of complexity on the genetic modeling of oligogenicity. (+info)
Bardet-Biedl syndrome associated with vaginal atresia: a case report.
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This is a case report of Bardet-Biedl syndrome associated with vaginal atresia diagnosed in a 15-year-old girl. She had mild mental retardation; obesity; nistagmus, retinitis pigmentosa and optic atrophy in both eyes; accessory digit on the left hand; polydactyly in lower extremities; a mobile, painful, nonfixed mass of 6 cm in diameter in the pelvic region; a palpable cystic mass in front of the rectal wall; and no vaginal opening. Secondary sex characteristics were determined. The vaginal atresia was distinguished from vaginal agenesis by the presence of proximal vagina in radiological examination. (+info)
The oligogenic properties of Bardet-Biedl syndrome.
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Bardet-Biedl syndrome (BBS: OMIM 209900) is a rare developmental disorder that exhibits significant clinical and genetic heterogeneity. Although modeled initially as a purely recessive trait, recent data have unmasked an oligogenic mode of disease transmission, in which mutations at different BBS loci can interact genetically in some families to cause and/or modify the phenotype. Here, I will review and discuss recent advances in elucidating both genetic and cellular aspects of this phenotype and their potential application in understanding the genetic basis of phenotypic variability and oligogenic inheritance. (+info)
Comparative genomics identifies a flagellar and basal body proteome that includes the BBS5 human disease gene.
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Cilia and flagella are microtubule-based structures nucleated by modified centrioles termed basal bodies. These biochemically complex organelles have more than 250 and 150 polypeptides, respectively. To identify the proteins involved in ciliary and basal body biogenesis and function, we undertook a comparative genomics approach that subtracted the nonflagellated proteome of Arabidopsis from the shared proteome of the ciliated/flagellated organisms Chlamydomonas and human. We identified 688 genes that are present exclusively in organisms with flagella and basal bodies and validated these data through a series of in silico, in vitro, and in vivo studies. We then applied this resource to the study of human ciliation disorders and have identified BBS5, a novel gene for Bardet-Biedl syndrome. We show that this novel protein localizes to basal bodies in mouse and C. elegans, is under the regulatory control of daf-19, and is necessary for the generation of both cilia and flagella. (+info)
Bardet-Biedl syndrome type 4 (BBS4)-null mice implicate Bbs4 in flagella formation but not global cilia assembly.
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The functions of the proteins encoded by the Bardet-Biedl syndrome (BBS) genes are unknown. Mutations in these genes lead to the pleiotropic human disorder BBS, which is characterized by obesity, retinopathy, polydactyly, renal and cardiac malformations, learning disabilities, and hypogenitalism. Secondary features include diabetes mellitus and hypertension. Recently, it has been suggested that the BBS phenotypes are the result of a lack of cilia formation or function. In this study, we show that mice lacking the Bbs4 protein have major components of the human phenotype, including obesity and retinal degeneration. We show that Bbs4-null mice develop both motile and primary cilia, demonstrating that Bbs4 is not required for global cilia formation. Interestingly, male Bbs4-null mice do not form spermatozoa flagella, and BBS4 retinopathy involves apoptotic death of photoreceptors, the primary ciliated cells of the retina. These mutation data demonstrate a connection between the function of a BBS protein and cilia. To further evaluate an association between cilia and BBS, we performed homology comparisons of BBS proteins in model organisms and find that BBS proteins are specifically conserved in ciliated organisms. (+info)
Cilia and flagella revealed: from flagellar assembly in Chlamydomonas to human obesity disorders.
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The recent identification in Chlamydomonas of the intraflagellar transport machinery that assembles cilia and flagella has triggered a renaissance of interest in these organelles that transcends studies on their well-characterized ability to move. New studies on several fronts have revealed that the machinery for flagellar assembly/disassembly is regulated by homologs of mitotic proteins, that cilia play essential roles in sensory transduction, and that mutations in cilia/basal body proteins are responsible for cilia-related human disorders from polycystic kidney disease to a syndrome associated with obesity, hypertension, and diabetes. (+info)
Antenatal renal sonographic anomalies and postnatal follow-up of renal involvement in Bardet-Biedl syndrome.
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OBJECTIVES: To describe an antenatal sonographic renal pattern encountered in Bardet-Biedl syndrome, a rare autosomal recessive disorder whose definitive diagnosis is often delayed, and to describe the evolution of the sonographic appearance of the kidneys after birth. METHODS: Among a large group of fetuses with hyperechoic kidneys, we retrospectively analyzed the prenatal sonographic findings and clinical and postnatal renal sonographic evolution of 11 patients who were found to be affected by Bardet-Biedl syndrome. RESULTS: All 11 fetuses presented enlarged homogeneously hyperechoic kidneys without corticomedullary differentiation. The diagnosis was established before birth in three fetuses thanks to their familial history. It was confirmed during childhood in the remaining eight based on the development of the classic features of the syndrome. In the postnatal period, the prenatal pattern persisted for a few months in all 11 cases. The sonographic aspects of the kidneys normalized in most cases between 1 and 2 years after birth. CONCLUSIONS: In affected families, the prenatal appearance of enlarged hyperechoic kidneys without corticomedullary differentiation should prompt a diagnosis of recurrence in the family of Bardet-Biedl syndrome, especially when polydactyly is present. In non-affected families, Bardet-Biedl syndrome should be included in the differential diagnosis whenever such an appearance is discovered in utero. The postnatal evolution of the renal sonographic findings is variable and normalization generally occurs by the age of 2 years. (+info)
Comparative genomic analysis identifies an ADP-ribosylation factor-like gene as the cause of Bardet-Biedl syndrome (BBS3).
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Bardet-Biedl syndrome (BBS) is a genetically heterogeneous, pleiotropic human disorder characterized by obesity, retinopathy, polydactyly, renal and cardiac malformations, learning disabilities, and hypogenitalism. Eight BBS loci have been mapped, and seven genes have been identified. BBS3 was previously mapped to chromosome 3 by linkage analysis in a large Israeli Bedouin kindred. The rarity of other families mapping to the BBS3 locus has made it difficult to narrow the disease interval sufficiently to identify the gene by positional cloning. We hypothesized that the genomes of model organisms that contained the orthologues to known BBS genes would also likely contain a BBS3 orthologue. Therefore, comparative genomic analysis was performed to prioritize BBS candidate genes for mutation screening. Known BBS proteins were compared with the translated genomes of model organisms to identify a subset of organisms in which these proteins were conserved. By including multiple organisms that have relatively small genome sizes in the analysis, the number of candidate genes was reduced, and a few genes mapping to the BBS3 interval emerged as the best candidates for this disorder. One of these genes, ADP-ribosylation factor-like 6 (ARL6), contains a homozygous stop mutation that segregates completely with the disease in the Bedouin kindred originally used to map the BBS3 locus, identifying this gene as the BBS3 gene. These data illustrate the power of comparative genomic analysis for the study of human disease and identifies a novel BBS gene. (+info)