A gene for cleidocranial dysplasia maps to the short arm of chromosome 6.

Cleidocranial dysplasia (CCD) is an autosomal dominant generalized bone dysplasia characterized by mild-to-moderate short stature, clavicular aplasia or hypoplasia, supernumerary and ectopic teeth, delayed eruption of secondary teeth, a characteristic craniofacial appearance, and a variety of other skeletal anomalies. We have performed linkage studies in five families with CCD, with 24 affected and 20 unaffected individuals, using microsatellite markers spanning two candidate regions on chromosomes 8q and 6. The strongest support for linkage was with chromosome 6p microsatellite marker D6S282 with a two-point lod score of 4.84 (theta = .03). Furthermore, the multipoint lod score was 5.70 in the interval between D6S282 and D6S291. These data show that the gene for autosomal dominant CCD is located within a 19-cM interval on the short arm of chromosome 6, between D6S282 and D6S291.     

Repositioning the hereditary paraganglioma critical region on chromosome band 11q23

Hereditary paragangliomas (PGL, glomus tumors, MIM no.168000) are mostly benign, slow-growing tumors of the head and neck region. The gene (or genes) affecting risk to PGL are subject to genomic imprinting: children of affected fathers exhibit an autosomal dominant pattern of disease inheritance, whereas children of affected mothers rarely if ever develop the disease through maternal transmission. We previously confined the disease gene to an approximately 6 Mb critical region on chromosome band 11q23 (PGL1). Based on haplotype analysis of an extended Dutch pedigree, a 2 Mb sub-region between D11S938 and D11S1885 was proposed as the PGL1 critical interval. In this study, we excluded this interval by analysis of two new single tandem repeat polymorphisms (STRP) contained therein. Instead, we predicted a non-overlapping, more proximal 2 Mb critical interval between D11S1647 and D11S897, and evaluated this new region using nine STRP (D11S1986, five new, closely-linked STRP, D11S1347, D11S3178, and D11S1987). Consistent with our prediction, we observed substantial haplotype-sharing within the Dutch pedigree. We also analyzed four new American PGL families. A recombination event detected in one family further defined D11S1347 as the new telomeric border. We observed significant haplotype-sharing within this new interval among three unrelated American PGL families, strongly suggesting that they originated from a common ancestor. Thus, we confined PGL1 to an approximately 1.5 Mb region between D11S1986 and D11S1347, and showed identity-by-descent sharing for a group of American PGL families. Received: 2 November 1998 / Accepted: 21 December 1998     

The Usher syndrome in the Lebanese population and further refinement of the USH2A candidate region

Usher syndrome (USH) is an autosomal-recessive disease characterized by neurosensory deafness and progressive retinitis pigmentosa. So far, three clinical types of Usher syndrome have been defined, and are caused by defects at more than eight loci. We report the linkage analysis of seven Lebanese families with Usher syndrome, two with type I (USH1) and five with type II (USH2). We demonstrate that one family is linked to the USH1C locus, a rare form of USH1 only reported in the French Acadian population. Linkage analysis of the five USH2 families with recently mapped loci allowed us to reduce the USH2A candidate region to a very small interval flanked by D1S2646/D1S2629 and D1S2827. Furthermore, haplotype comparison between the different families suggests a founder effect for the USH2A mutation among the different Lebanese ethnic groups, while a genetic heterogeneity is noted for Usher syndrome type I. Received: 9 January 1998 / Accepted: 23 March 1998     

Mutations of MYO6 are associated with recessive deafness,DFNB37

Cosegregation of profound, congenital deafness with markers on chromosome 6q13 in three Pakistani families defines a new recessive deafness locus, DFNB37. Haplotype analyses reveal a 6-cM linkage region, flanked by markers D6S1282 and D6S1031, that includes the gene encoding unconventional myosin VI. In families with recessively inherited deafness, DFNB37, our sequence analyses of MYO6 reveal a frameshift mutation (36-37insT), a nonsense mutation (R1166X), and a missense mutation (E216V). These mutations, along with a previously published missense allele linked to autosomal dominant progressive hearing loss (DFNA22), provide an allelic spectrum that probes the relationship between myosin VI dysfunction and the resulting phenotype.     

WISP3, the gene responsible for the human skeletal disease progressive pseudorheumatoid dysplasia, is not essential for skeletal function in mice

In humans, loss-of-function mutations in WISP3 cause the autosomal recessive skeletal disease progressive pseudorheumatoid dysplasia (PPD) (Online Mendelian Inheritance in Man database number 208230). WISP3 encodes Wnt1-inducible signaling protein 3, a cysteine-rich, multidomain, secreted protein, whose paralogous CCN (connective tissue growth factor/cysteine-rich protein 61/nephroblastoma overexpressed) family members have been implicated in diverse biologic processes including skeletal, vascular, and neural development. To understand the role of WISP3 in the skeleton, we targeted the Wisp3 gene in mice by creating a mutant allele comparable to that which causes human disease. We also created transgenic mice that overexpress human WISP3 in cartilage. Surprisingly, homozygous Wisp3 mutant mice appear normal and do not recapitulate any of the morphological, radiographic, or histological abnormalities seen in patients with PPD. Mice that overexpress WISP3 are also normal. We conclude, that in contrast to humans, Wisp3 is not an essential participant during skeletal growth or homeostasis in mice.     

Refined mapping of the gene for autosomal dominant retinitis pigmentosa (RP17) on chromosome 17q22

Linkage analysis was performed on a large Dutch family with autosomal dominant retinitis pigmentosa. Linkage was found to the RP17 locus on chromosome 17q22, which was previously described in two South African families by Bardien et al. (1995, 1997). Assuming that the disease phenotypes in these families are caused by the same gene, the RP17 critical region is refined to a 7.7-cM interval between markers D17S1607 and D17S948. Two positional candidate genes, the retina-specific amine oxidase (RAO) gene (AOC2) and the cone transducin γ gene (GNGT2), were excluded. Received: 7 September 1998 / Accepted: 23 November 1998     

Homozygous mutations in IHH cause acrocapitofemoral dysplasia,an autosomal recessive disorder with cone-shaped epiphyses in hands and hips

Acrocapitofemoral dysplasia is a recently delineated autosomal recessive skeletal dysplasia, characterized clinically by short stature with short limbs and radiographically by cone-shaped epiphyses, mainly in hands and hips. Genomewide homozygosity mapping in two consanguineous families linked the locus to 2q35-q36 with a maximum two-point LOD score of 8.02 at marker D2S2248. Two recombination events defined the minimal critical region between markers D2S2248 and D2S2151 (3.74 cM). Using a candidate-gene approach, we identified two missense mutations in the amino-terminal signaling domain of the gene encoding Indian hedgehog (IHH). Both affected individuals of family 1 are homozygous for a 137C-->T transition (P46L), and the three patients in family 2 are homozygous for a 569T-->C transition (V190A). The two mutant amino acids are strongly conserved and predicted to be located outside the region where brachydactyly type A-1 mutations are clustered.     

A gene responsible for Ghosal hemato-diaphyseal dysplasia maps to chromosome 7q33–34

Ghosal hemato-diaphyseal dysplasia is a rare autosomal recessive disorder characterized by a progressive sclerosing diaphyseal dysplasia and refractory anemia. The pathogenesis and genetic bases of this syndrome remain hitherto unknown. We have performed a genome wide search in two inbred families originating from Algeria and Tunisia. Here, we report on the mapping of a disease gene to chromosome 7q33–34 (Z _max = 4.21 at θ = 0 at locus D7S2513) in a 3.4 Mb defined by loci D7S2560 and AC091742. Ongoing studies will hopefully lead to identification of the disease-causing gene.     

Genetic mapping of the Camurati-Engelmann disease locus to chromosome 19q13.1-q13.3

Camurati-Engelmann disease (CED [MIM 131300]), or progressive diaphyseal dysplasia, is an autosomal dominant sclerosing bone dysplasia characterized by progressive bone formation along the periosteal and endosteal surfaces at the diaphyseal and metaphyseal regions of long bones and cranial hyperostosis, particularly at the skull base. The gene for CED, or its chromosomal localization, has not yet been identified. We performed a genomewide linkage analysis of two unrelated Japanese families with CED, in which a total of 27 members were available for this study; 16 of them were affected with the disease. Two-point linkage analysis revealed a maximum LOD score of 7.41 (recombination fraction.00; penetrance 1.00) for the D19S918 microsatellite marker locus. Haplotype analysis revealed that all the affected individuals shared a common haplotype observed, in each family, between D19S881 and D19S606, at chromosome 19q13.1-q13.3. These findings, together with a genetic distance among the marker loci, indicate that the CED locus can be assigned to a 15.1-cM segment between D19S881 and D19S606.     

Linkage analysis of the nail-patella syndrome.

Nail-patella syndrome (NPS) is an autosomal dominant disorder characterized by dysplasia of nails and patella, decreased mobility of the elbow, iliac horns, and, in some cases, nephropathy. The disorder has been mapped to the long arm of chromosome 9, but the precise localization and identity of the NPS gene are unknown. Linkage analysis in three NPS families, using highly informative dinucleotide repeat polymorphisms on 9q33-q34, confirmed linkage of NPS to this chromosome. Recombinations were detected, by two-point linkage analysis, between NPS and the centromeric markers D9S60 and the gelsolin gene and the telomeric markers D9S64 and D9S66, in one of the families. Haplotype analysis suggested an additional recombination between NPS and the argininosuccinate synthetase (ASS) gene. These results localize the NPS gene to an interval on 9q34.1, distal to D9S60 and proximal to ASS, comprising a genetic distance of approximately 9 cM. This represents a significant refinement in the localization of the NPS gene.     

Localization of the Netherton syndrome gene to chromosome 5q32, by linkage analysis and homozygosity mapping

Netherton syndrome (NS [MIM 256500]) is a rare and severe autosomal recessive disorder characterized by congenital ichthyosis, a specific hair-shaft defect (trichorrhexis invaginata), and atopic manifestations. Infants with this syndrome often fail to thrive; life-threatening complications result in high postnatal mortality. We report the assignment of the NS gene to chromosome 5q32, by linkage analysis and homozygosity mapping in 20 families affected with NS. Significant evidence for linkage (maximum multipoint LOD score 10.11) between markers D5S2017 and D5S413 was obtained, with no evidence for locus heterogeneity. Analysis of critical recombinants mapped the NS locus between markers D5S463 and D5S2013, within an <3.5-cM genetic interval. The NS locus is telomeric to the cytokine gene cluster in 5q31. The five known genes encoding casein kinase Ialpha, the alpha subunit of retinal rod cGMP phosphodiesterase, the regulator of mitotic-spindle assembly, adrenergic receptor beta2, and the diastrophic dysplasia sulfate-transporter gene, as well as the 38 expressed-sequence tags mapped within the critical region, are not obvious candidates. Our study is the first step toward the positional cloning of the NS gene. This finding promises a better understanding of the molecular mechanisms that control epidermal differentiation and immunity.     

Bone dysplasia sclerosteosis results from loss of the SOST gene product, a novel cystine knot-containing protein

Sclerosteosis is an autosomal recessive sclerosing bone dysplasia characterized by progressive skeletal overgrowth. The majority of affected individuals have been reported in the Afrikaner population of South Africa, where a high incidence of the disorder occurs as a result of a founder effect. Homozygosity mapping in Afrikaner families along with analysis of historical recombinants localized sclerosteosis to an interval of approximately 2 cM between the loci D17S1787 and D17S930 on chromosome 17q12-q21. Here we report two independent mutations in a novel gene, termed "SOST." Affected Afrikaners carry a nonsense mutation near the amino terminus of the encoded protein, whereas an unrelated affected person of Senegalese origin carries a splicing mutation within the single intron of the gene. The SOST gene encodes a protein that shares similarity with a class of cystine knot-containing factors including dan, cerberus, gremlin, prdc, and caronte. The specific and progressive effect on bone formation observed in individuals affected with sclerosteosis, along with the data presented in this study, together suggest that the SOST gene encodes an important new regulator of bone homeostasis.     

Mutation of the start codon in the FRDA1 gene: linkage analysis of three pedigrees with the ATG to ATT transversion points to a unique common ancestor

Friedreich ataxia (FRDA) is a progressive neurodegenerative disorder caused by loss-of-function mutations in the gene encoding frataxin. Most patients with FRDA have trinucleotide repeat expansions in both alleles of the FRDA1 gene. In patients heterozygous for the expansion the second allele may be inactivated by a point mutation. We identified the ATG→ATT (M1I) mutation of the start codon in three independent families. Individuals with symptoms of FRDA in these families are compound heterozygous for the repeat expansion and the ATG mutation. To look for a common founder of the M1I mutation, a detailed linkage analysis employing six polymorphic chromosome 9 markers was performed. We found complete haplotype identity for two of the three chromosomes with the point mutation. The third case shows partial conformity and may be the result of a single recombination event. Received: 13 February 1998 / Accepted: 18 March 1998     

The human neuregulin-2 (NRG2) gene: cloning, mapping and evaluation as a candidate for the autosomal recessive form of Charcot-Marie-Tooth disease linked to 5q

Neuregulin-2 (NRG2) is a novel member of the neuregulin family of growth and differentiation factors. Through interaction with the ErbB family of receptors, neuregulin-2 induces the growth and differentiation of epithelial, neuronal, glial and other types of cells. In this study, we have cloned the human neuregulin-2 gene, and determined its genomic structure and alternative splicing patterns. By using radiation hybrid mapping panels, the human NRG2 gene was mapped to the D5S658–D5S402 region within 5q23–q33, close to an autosomal recessive form of demyelinating Charcot-Marie-Tooth (CMT) disease. The NRG2 gene was found to be on two yeast artificial chromosomes overlapping the candidate interval and was, thus, considered a good positional candidate for this form of CMT. When the entire neuregulin-2 coding sequence and splice junctions were explored, however, no mutation was identified in one CMT family linked to 5q23–q33. In addition, three intronic single nucleotide polymorphisms were identified in the NRG2 gene. Genotyping in two families localized the NRG2 gene outside of the revised candidate interval between D5S402–D5S210 and excluded NRG2 as the gene responsible for this form of CMT disease. Received: 11 December 1998 / Accepted: 19 January 1998     

Assignment of the locus for PLO-SL, a frontal-lobe dementia with bone cysts, to 19q13.

PLO-SL (polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy) is a recessively inherited disorder characterized by systemic bone cysts and progressive presenile frontal-lobe dementia, resulting in death at <50 years of age. Since the 1960s, approximately 160 cases have been reported, mainly in Japan and Finland. The pathogenesis of the disease is unknown. In this article, we report the assignment of the locus for PLO-SL, by random genome screening using a modification of the haplotype-sharing method, in patients from a genetically isolated population. By screening five patient samples from 2 Finnish families, followed by linkage analysis of 12 Finnish families, 3 Swedish families, and 1 Norwegian family, we were able to assign the PLO-SL locus to a 9-cM interval between markers D19S191 and D19S420 on chromosome 19q13. The critical region was further restricted, to approximately 1.8 Mb, by linkage-disequilibrium analysis of the Finnish families. According to the haplotype analysis, one Swedish and one Norwegian PLO-SL family are not linked to the chromosome 19 locus, suggesting that PLO-SL is a heterogeneous disease. In this chromosomal region, one potential candidate gene for PLO-SL, the gene encoding amyloid precursor-like protein 1, was analyzed, but no mutations were detected in the coding region.     

Juvenile hemochromatosis locus maps to chromosome 1q

Juvenile hemochromatosis (JH) is an autosomal recessive disorder that leads to severe iron loading in the 2d to 3d decade of life. Affected members in families with JH do not show linkage to chromosome 6p and do not have mutations in the HFE gene that lead to the common hereditary hemochromatosis. In this study we performed a genomewide search to map the JH locus in nine families: six consanguineous and three with multiple affected patients. This strategy allowed us to identify the JH locus on the long arm of chromosome 1. A maximum LOD score of 5.75 at a recombination fraction of 0 was detected with marker D1S498, and a LOD score of 5. 16 at a recombination fraction of 0 was detected for marker D1S2344. Homozygosity mapping in consanguineous families defined the limits of the candidate region in an approximately 4-cM interval between markers D1S442 and D1S2347. Analysis of genes mapped in this interval excluded obvious candidates. The JH locus does not correspond to the chromosomal localization of any known gene involved in iron metabolism. These findings provide a means to recognize, at an early age, patients in affected families. They also provide a starting point for the identification of the affected gene by positional cloning.     

Possible genetic heterogeneity in the Saethre-Chotzen syndrome

Saethre-Chotzen syndrome is an autosomal dominant acrocephalosyndactyly syndrome whose gene has been assigned to chromosome 7p. Cytogenetic and linkage analyses have enabled the interval encompassing the disease gene to be delimited to a short region of chromosome 7p15.3–p21.2. Based on the genetic analysis of three unreported families, we confirm the location of the disease gene(s) in the interval defined by loci D7S664 and D7S493 (Z_max = 4.78 at * = 0 at the D7S488 locus) but fail to decide whether one or more disease-causing genes map in this genetic interval. Received: 2 January 1996 / Revised: 21 March 1996     

Benign recurrent intrahepatic cholestasis (BRIC): evidence of genetic heterogeneity and delimitation of the BRIC locus to a 7-cM interval between D18S69 and D18S64

Benign recurrent intrahepatic cholestasis (BRIC) is an autosomal recessive liver disease characterized by multiple episodes of cholestasis without progression to chronic liver disease. The gene was previously assigned to chromosome 18q21, using a shared segment analysis in three families from the Netherlands. In the present study we report the linkage analysis of an expanded sample of 14 BRIC families, using 15 microsatellite markers from the 18q21 region. Obligate recombinants in two families place the gene in a 7-cM interval, between markers D18S69 and D18S64. All intervening markers had significant LOD scores in two-point linkage analysis. Moreover, we identified one family in which the BRIC gene seems to be unlinked to the 18q21 region, or that represents incomplete penetrance of the BRIC genotype. Received: 6 March 1997 / Accepted: 26 March 1997     

Autosomal dominant cerebellar ataxia type III: linkage in a large British family to a 7.6-cM region on chromosome 15q14-21.3.

Autosomal dominant cerebellar ataxia type III (ADCA III) is a relatively benign, late-onset, slowly progressive neurological disorder characterized by an uncomplicated cerebellar syndrome. Three loci have been identified: a moderately expanded CAG trinucleotide repeat in the SCA 6 gene, the SCA 5 locus on chromosome 11, and a third locus on chromosome 22 (SCA 10). We have identified two British families in which affected individuals do not have the SCA 6 expansion and in which the disease is not linked to SCA 5 or SCA 10. Both families exhibit the typical phenotype of ADCA III. Using a genomewide searching strategy in one of these families, we have linked the disease phenotype to marker D15S1039. Construction of haplotypes has defined a 7.6-cM interval between the flanking markers D15S146 and D15S1016, thereby assigning another ADCA III locus to the proximal long-arm of chromosome 15 (SCA 11). We excluded linkage of the disease phenotype to this region in the second family. These results indicate the presence of two additional ADCA III loci and more clearly define the genetic heterogeneity of ADCA III.     

Human Rod Monochromacy: Linkage Analysis and Mapping of a Cone Photoreceptor Expressed Candidate Gene on Chromosome 2q11

We have performed linkage analysis in eight families with rod monochromacy, an autosomal recessively inherited condition with complete color blindness. Significant linkage was found with markers located at the pericentromeric region of chromosome 2. A maximum lod score of 5.36 was obtained for marker D2S2333 at θ = 0.00. Mapping of meiotic breakpoints localized the disease gene between markers D2S2187 and D2S2229. Homozygosity for a number of subsequent markers indicating identity by descent was found in two families and provides evidence for a further refinement of the locus proximal to D2S373. This defines an interval of ≈3 cM covering theACHM2locus for rod monochromacy. Radiation hybrid mapping of theCNGA3gene encoding the α-subunit of the cGMP gated cation channel in human cone photoreceptors resulted in a maximum lod score of 16.1 with marker D2S2311 combined with a calculated physical distance of 6.19cR_10,000. Screening of the CEPH YAC library and subsequent STS mapping indicated the physical order cen–D2S2222–D2S2175–(D2S2187/D2S2311)–qtel ofmarkers on 2q11 and showed that theCNGA3gene maps most closely to D2S2187 and D2S2311. These data indicate that theCNGA3gene maps within the critical interval of theACHM2locus for rod monochromacy and thus is a candidate gene for this disease.