Bardet-Biedl Syndrome in an African-American patient: should the diagnostic criteria be expanded to include hydrometrocolpos?

Bardet-Biedl Syndrome (BBS) is a multisystemic disorder diagnosed on the basis of a combination of primary and secondary clinical features that include retinal dystrophy, obesity, polydactyly, cognitive dysfunction, and renal malformations. We report a unique case of BBS in a 13-year old girl of African-American descent who presented with retinitis pigmentosa, obesity, polydactyly, learning disabilities, precocious puberty, hypertension, renal cysts, and Hirschprung disease. Further evaluation revealed a history of precocious puberty, which is antithetical to the common manifestations of BBS, while neuroimaging was suggestive of periventricular leukomalacia and neuro-electrophysiologic studies revealed diffuse cerebral disturbance, which may contribute to her neurological abnormalities. The patient was also diagnosed with hydrometrocolpos, a finding typical of McKusick-Kaufman Syndrome (MKKS) but infrequent in other disorders. This observation, together with recent findings in some mouse models of BBS, raises the question of whether hydrometrocolpos should be considered as an additional diagnostic criterion for BBS to be used in females in parallel to the criterion of hypogonadism in males, thereby improving diagnostic sensitivity.

A 60-year tale of spots, maps, and genes.

This is an account of almost 60 years' experience in the clinical delineation of genetic disorders, mapping genes on chromosomes, and cataloging human disease-related genes and genetic disorders. The origins of medical genetics as a clinical specialty, of the Human Genome Project, of genomics (including the term), and of HUGO are recounted.

Online Mendelian Inheritance in Man (OMIM), a knowledgebase of human genes and genetic disorders.

Online Mendelian Inheritance in Man (OMIM) is a comprehensive, authoritative and timely knowledgebase of human genes and genetic disorders compiled to support human genetics research and education and the practice of clinical genetics. Started by Dr Victor A. McKusick as the definitive reference Mendelian Inheritance in Man, OMIM (http://www.ncbi.nlm.nih.gov/omim/) is now distributed electronically by the National Center for Biotechnology Information, where it is integrated with the Entrez suite of databases. Derived from the biomedical literature, OMIM is written and edited at Johns Hopkins University with input from scientists and physicians around the world. Each OMIM entry has a full-text summary of a genetically determined phenotype and/or gene and has numerous links to other genetic databases such as DNA and protein sequence, PubMed references, general and locus-specific mutation databases, HUGO nomenclature, MapViewer, GeneTests, patient support groups and many others. OMIM is an easy and straightforward portal to the burgeoning information in human genetics.

Rare autosomal recessive cardiac valvular form of Ehlers-Danlos syndrome results from mutations in the COL1A2 gene that activate the nonsense-mediated RNA decay pathway.

Splice site mutations in the COL1A2 gene of type I collagen can give rise to forms of Ehlers-Danlos syndrome (EDS) because of partial or complete skipping of exon 6, as well as to mild, moderate, or lethal forms of osteogenesis imperfecta as a consequence of skipping of other exons. We identified three unrelated individuals with a rare recessively inherited form of EDS (characterized by joint hypermobility, skin hyperextensibility, and cardiac valvular defects); in two of them, COL1A2 messenger RNA (mRNA) instability results from compound heterozygosity for splice site mutations in the COL1A2 gene, and, in the third, it results from homozygosity for a nonsense codon. The splice site mutations led to use of cryptic splice donor sites, creation of a downstream premature termination codon, and extremely unstable mRNA. In the wild-type allele, the two introns (IVS11 and IVS24) in which these mutations occurred were usually spliced slowly in relation to their respective immediate upstream introns. In the mutant alleles, the upstream intron was removed, so that exon skipping could not occur. In the context of the mutation in IVS24, computer-generated folding of a short stretch of mRNA surrounding the mutation site demonstrated realignment of the relationships between the donor and acceptor sites that could facilitate use of a cryptic donor site. These findings suggest that the order of intron removal is an important variable in prediction of mutation outcome at splice sites and that folding of the nascent mRNA could be one element that contributes to determination of order of splicing. The complete absence of pro alpha 2(I) chains has the surprising effect of producing cardiac valvular disease without bone involvement.

The major mutation in the RMRP gene causing CHH among the Amish is the same as that found in most Finnish cases.

Cartilage-hair hypoplasia (CHH), or McKusick type metaphyseal chondrodysplasia, was originally described in the Old Order Amish in the United States and subsequently found to be unusually frequent among Finns. The major mutation causing CHH in Finns is a 70A --> G nucleotide substitution in the RMRP gene, which encodes the untranslated RNA that is a component of mitochondrial RNA-processing endoribonuclease. Here we report that the same mutation is the most frequent one, perhaps the only one, in the Amish population in which CHH was first characterized. The fact that the mutation segregates with the same major haplotype in these two populations and others suggests that it is very ancient. Unlike some other ordinarily rare recessive disorders that are limited in their high frequency to a single Amish deme (subisolate), e.g., Ellis-van Creveld syndrome, CHH occurs in high frequency in at least three distinct Amish demes, indicating, along with genealogic data, that there were multiple heterozygotes among the founders, as proposed by McKusick et al. [1965: Bull Johns Hopkins Hosp 116:231-272].

A novel dysmorphic syndrome with open calvarial sutures and sutural cataracts maps to chromosome 14q13-q21.

We describe a new dysmorphic syndrome in an inbred Saudi Arabian family with 21 members. Five males and one female have similar craniofacial features including wide open calvarial sutures with large and late-closing anterior fontanels, frontal bossing, hyperpigmentation with capillary hemangioma of the forehead, significant hypertelorism, and a broad and prominent nose. In addition, these individuals have Y-shaped sutural cataracts diagnosed by 1-2 years of age. No chromosomal or biochemical abnormalities were identified. A genome-wide scan was performed, and two-point LOD score analysis, assuming autosomal recessive inheritance, detected linkage to chromosome 14q13-q21. The highest LOD scores were obtained for marker GATA136A04 (LOD=4.58 at theta=0.00) and for the adjacent telomeric marker D14S1048 (LOD=4.32 at theta=0.00). Multipoint linkage analysis resulted in a maximum LOD score of 5.44 between markers D14S1048 and GATA136A04. Model independent analysis by SIBPAL confirmed linkage to the same chromosomal region. Haplotype analysis indicated that all affected individuals were homozygous for the interval on chromosome 14q13-q21 with two recombinants for D14S1014 (centromeric) and one recombinant for D14S301 (telomeric). These recombinations limit the disease locus to a region of approximately 7.26 Mb. Candidate genes localized to this region were identified, and analysis of PAX9 did not identify mutations in these patients. The unique clinical phenotype and the mapping data suggest that this family represents a novel autosomal recessive syndrome.

SPG20 is mutated in Troyer syndrome, an hereditary spastic paraplegia.

Troyer syndrome (TRS) is an autosomal recessive complicated hereditary spastic paraplegia (HSP) that occurs with high frequency in the Old Order Amish. We report mapping of the TRS locus to chromosome 13q12.3 and identify a frameshift mutation in SPG20, encoding spartin. Comparative sequence analysis indicates that spartin shares similarity with molecules involved in endosomal trafficking and with spastin, a molecule implicated in microtubule interaction that is commonly mutated in HSP.

Online Mendelian Inheritance in Man (OMIM), a knowledgebase of human genes and genetic disorders.

Online Mendelian Inheritance in Man (OMIM) is a comprehensive, authoritative and timely knowledgebase of human genes and genetic disorders compiled to support research and education in human genomics and the practice of clinical genetics. Started by Dr Victor A. McKusick as the definitive reference Mendelian Inheritance in Man, OMIM (www.ncbi.nlm.nih.gov/omim) is now distributed electronically by the National Center for Biotechnology Information (NCBI), where it is integrated with the Entrez suite of databases. Derived from the biomedical literature, OMIM is written and edited at Johns Hopkins University with input from scientists and physicians around the world. Each OMIM entry has a full-text summary of a genetically determined phenotype and/or gene and has numerous links to other genetic databases such as DNA and protein sequence, PubMed references, general and locus-specific mutation databases, approved gene nomenclature, and the highly detailed mapviewer, as well as patient support groups and many others. OMIM is an easy and straightforward portal to the burgeoning information in human genetics.