Mapping of DNA markers linked to the cystic fibrosis locus on the long arm of chromosome 7.

We have used a panel of eight human/mouse somatic-cell hybrids, each containing various portions of human chromosome 7, and three patient cell lines with interstitial deletions on chromosome 7 for localization of six DNA markers linked to the cystic fibrosis locus. Our data suggest that D7S15 is located in the region 7 cen----q22, that MET is located in 7q22----31, and that D7S8 and 7C22 are located in q22----q32. The hybridization results for COL1A2 and TCRB are consistent with their previous assignment to 7q21----q22 and 7q32, respectively. Given the location of these six markers and their linkage relationships, it is probable that the cystic fibrosis locus is in either the distal region of band q22 or the proximal region of q31. Using the same set of cell lines, we have also examined the location of another chromosome 7 marker PGY1. The data show that PGY1 is located in the region 7cen----q22, a position very different from its previous assignment.     

Myotonia congenita: novel mutations in CLCN1 gene

Myotonia congenita belongs to the group of non-dystrophic myotonia caused by mutations of CLCN1gene, which encodes human skeletal muscle chloride channel 1. It can be inherited either in autosomal dominant (Thomsen disease) or recessive (Becker disease) forms. Here we have sequenced all 23 exons and exon-intron boundaries of the CLCN1 gene, in a panel of 5 unrelated Chinese patients with myotonia congenita (2 with dominant and 3 with recessive form). In addition, detailed clinical analysis was performed in these patients to summarize their clinical characteristics in relation to their genotypes. Mutational analyses revealed 7 different point mutations. Of these, we have found 3 novel mutations including 2 missense (R47W, V229M), one splicing (IVS19+2T>C), and 4 known mutations (Y261C,G523D, M560T, G859D). Our data expand the spectrum of CLCN1 mutations and provide insights for genotype–phenotype correlations of myotonia congenita in the Chinese population.     

Myotonia congenita: novel mutations in CLCN1 gene

Myotonia congenita belongs to the group of non-dystrophic myotonia caused by mutations of CLCN1gene, which encodes human skeletal muscle chloride channel 1. It can be inherited either in autosomal dominant (Thomsen disease) or recessive (Becker disease) forms. Here we have sequenced all 23 exons and exon-intron boundaries of the CLCN1 gene, in a panel of 5 unrelated Chinese patients with myotonia congenita (2 with dominant and 3 with recessive form). In addition, detailed clinical analysis was performed in these patients to summarize their clinical characteristics in relation to their genotypes. Mutational analyses revealed 7 different point mutations. Of these, we have found 3 novel mutations including 2 missense (R47W, V229M), one splicing (IVS19+2T>C), and 4 known mutations (Y261C,G523D, M560T, G859D). Our data expand the spectrum of CLCN1 mutations and provide insights for genotype–phenotype correlations of myotonia congenita in the Chinese population.     

Myotonia congenita (Thomsen's disease) excluded from the region of the myotonic dystrophy locus on chromosome 19

Summary Linkage analysis has been carried out in six German families with autosomal dominantly inherited myotonia congenita (Thomsen's disease) using five chromosome 19 markers known to be linked to the gene for myotonic dystrophy (DM). Two of the markers, APOC1 and APOC2, are tightly linked to DM. Close linkage between these markers and myotonia congenita (MC) has been excluded to a distance of 9cM (z=-2.158). These data support the clinical suggestion that MC and DM are non-allelic disorders.     

The genes for the highly homologous Ca(2+)-binding proteins oncomodulin and parvalbumin are not linked in the human genome.

The chromosomal loci of the human parvalbumin and oncomodulin single-copy genes that encode structurally and evolutionarily closely related Ca(2+)-binding proteins were determined by somatic cell hybrid analysis. Southern blot analysis of genomic DNA from 25 human-hamster somatic cell hybrids showed that the human gene for oncomodulin resides on chromosome 7. Analysis of human-mouse hybrids selectively retaining human chromosome 7 or a portion of it allowed specific assignment of the gene locus to the p11-p13 region of chromosome 7 known to be mutated or deleted in patients with the Greig cephalopolysyndactyly syndrome. By gene dosage analysis on Southern blots, we showed that the gene for human parvalbumin maps distally to the cat eye syndrome marker D22S9 on chromosome 22q. Using somatic cell hybrids containing parts of human chromosome 22, the parvalbumin gene was sublocalized to the region 22q12-q13.1. This region contains a linkage group that maps to mouse chromosome 15, region E, and includes the SIS, ARSA, and DIA 1 genes. Our findings are consistent with the recent localization of the mouse parvalbumin gene to this region by two independent methods (C. H. Zühlke et al., 1989, Genet. Res. 54:37-43; S. Adolph et al., 1989, Cytogenet. Cell Genet. 52:177-179).     

Establishment of the mouse chromosome 7 region with homology to the myotonic dystrophy region of human chromosome 19q

A number of genetic markers, including ATP1A3, TGFB, CKMM, and PRKCG, define the genetic region on human chromosome 19 containing the myotonic dystrophy locus. These and a number of other DNA probes have been mapped to mouse chromosome 7 utilizing a mouse Mus domesticus/Mus spretus interspecific backcross segregating for the genetic markers pink-eye dilution (p) and chinchilla (cch). The establishment of a highly syntenic group conserved between mouse chromosome 7 and human chromosome 19q indicates the likely position of the homologous gene locus to the human myotonic dystrophy gene on proximal mouse chromosome 7. In addition, we have mapped the muscle ryanodine receptor gene (Ryr) to mouse chromosome 7 and demonstrated its close linkage to the Atpa-2, Tgfb-1, and Ckmm cluster of genes. In humans, the malignant hyperthermia susceptibility locus (MHS) also maps close to this gene cluster. The comparative mapping data support Ryr as a candidate gene for MHS.     

Fine mapping of a region of rat chromosome 12 close to the aspermia (as) locus and comparison with the human orthologous regions.

The aspermia mutation of the rat exhibits male sterility caused by arrest of spermatogenesis, which is controlled by an autosomal single recessive gene (as). The as locus has been mapped on rat chromosome 12. We recently identified a causative mutation for the aspermia phenotype of the as homozygous rats in the gene encoding Fkbp6, a member of the immunophilins FK506 binding proteins. In this paper, we report the fine mapping of the as locus by linkage analysis combined with comparative mapping using rat, mouse, and human genomic sequences and expression analysis of genes located in the as region. We constructed a fine linkage map of the region of rat chromosome 12 close to the as locus by using 13 microsatellite markers and localized the as locus to a 1.0-cM interval. Comparison of the linkage map with physical maps of rat, mouse, and human refined the as critical region in a 2.2-Mb segment of the rat physical map between the D12Nas3 and D12Nas8 genes, which includes the Fkbp6 gene. A centromeric part of this segment corresponds to the region commonly deleted in Williams syndrome, a human complex developmental disorder, on human chromosome 7q11.23. The expression analysis of 23 genes located on the 2.2-Mb segments in various mouse tissues identified genes exclusively or strongly expressed in the testis.     

cDNA and genomic cloning of HRC, a human sarcoplasmic reticulum protein, and localization of the gene to human chromosome 19 and mouse chromosome 7

Histidine-rich calcium binding protein (HRC) is a luminal sarcoplasmic reticulum (SR) protein of 165 kDa identified by virtue of its ability to bind 125I-labeled low-density lipoprotein with high affinity after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Hofmann et al., J. Biol. Chem. 264: 8260-8270, 1989). Its role in SR function is unknown. In this report, the gene encoding human HRC was localized to human chromosome 19 and mouse chromosome 7 by hybridization of a human HRC cDNA fragment to a panel of somatic cell hybrids. Known synteny between a portion of human chromosome 19 and a portion of mouse chromosome 7 and in situ hybridization of a biotin-labeled HRC probe to human chromosomes suggest a localization to a region corresponding to 19q13.3. The locus for myotonic dystrophy resides in the region 19q13.2-13.3. Therefore, we considered HRC, a muscle-specific gene, to possibly represent a "candidate gene" for myotonic muscular dystrophy. As a first step toward localizing HRC in relation to the myotonic dystrophy locus, we report the cloning of the human HRC gene, its intron-exon organization, and characterization of several informative polymorphisms to be used in future linkage studies in families with myotonic dystrophy. Of particular interest is an Alu-associated poly-d(GA) sequence located in an intron in the middle of the gene, and two stretches of acidic amino acids in the coding region of exon 1 that vary in length among different individuals.     

Identification of a novel gene on chromosome 7q31 that is interrupted by a translocation breakpoint in an autistic individual

The results of genetic linkage studies for autism have suggested that a susceptibility locus for the disease is located on the long arm of chromosome 7 (7q). An autistic individual carrying a translocation, t(7;13)(q31.3;q21), with the chromosome 7 breakpoint located in the region of 7q implicated by genetic studies was identified. A novel gene known as "RAY1" (or "FAM4A1") was found to be directly interrupted by the translocation breakpoint. The gene, which was found to be encoded by 16 exons with evidence of alternative splicing, spanned > or =220 kb of DNA at 7q31.3. Mutation screening of the entire coding region in a set of 27 unrelated autistic individuals failed to identify phenotype-specific variants, suggesting that coding region mutations are unlikely to be involved in the etiology of autism. Apparent homologues of RAY1 have also been identified in mouse, rat, pig, chicken, fruit fly, and nematode. The human and mouse genes share similar splicing patterns, and their predicted protein products are 98% identical.     

The human ryanodine receptor gene: Its mapping to 19q13.1, placement in a chromosome 19 linkage group, and exclusion as the gene causing myotonic dystrophy

The recent cloning of cDNA encoding the Ca++ release channel (ryanodine receptor) of human sarcoplasmic reticulum has enabled us to use somatic cell hybrids to localize the ryanodine receptor gene (RYR) to the proximal long arm of human chromosome 19. Studies with additional hybrids containing deletions or translocations in chromosome 19 enabled us to localize RYR to 19q13.1 in a region distal to GPI/MAG and proximal to D19S18/DNF11. On the basis that the myotonic dystrophy (DM) locus maps near this region and that myotonia could result from a defect in the ryanodine receptor, we examined the linkage between the DM locus and RYR. Our results, showing several DM-RYR recombinants, rule out an RYR defect as the cause of DM. However, localization of RYR to a region of human chromosome 19 which is syntenic to an area of pig chromosome 6 containing the HAL gene responsible for porcine malignant hyperthermia supports the candidacy of RYR for this disorder.     

Localization of the villin gene on human chromosome 2q35-q36 and on mouse chromosome 1

Summary A partial cDNA clone coding for the 110 carboxyterminal amino acids of human villin was used for mapping the human villin gene. In situ hybridization experiments on human chromosomes with tritiated probe allowed the regional localization of the villin locus to chromosome 2 at q35-36. Data obtained from restriction fragment length polymorphism analysis of two mouse species demonstrated the assignment of the villin gene to mouse chromosome 1 by assessment of linkage with the fast skeletal isoform of the myosin light-chain gene. These villin gene localizations add a fourth locus to the conserved gene cluster encoding the fast skeletal muscle isoform of the myosin light chain, isocitrate dehydrogenase, and the crystallins and confirm the partial homology of the human chromosome 2 long arm and mouse chromosome 1.     

Characterization of three novel human cadherin genes (CDH7, CDH19, and CDH20) clustered on chromosome 18q22-q23 and with high homology to chicken cadherin-7

Full-length coding sequences of two novel human cadherin cDNAs were obtained by sequence analysis of several EST clones and 5' and 3' rapid amplification of cDNA ends (RACE) products. Exons for a third cDNA sequence were identified in a public-domain human genomic sequence, and the coding sequence was completed by 3' RACE. One of the sequences (CDH7L1, HGMW-approved gene symbol CDH7) is so similar to chicken cadherin-7 gene that we consider it to be the human orthologue. In contrast, the published partial sequence of human cadherin-7 is identical to our second cadherin sequence (CDH7L2), for which we propose CDH19 as the new name. The third sequence (CDH7L3, HGMW-approved gene symbol CDH20) is almost identical to the mouse "cadherin-7" cDNA. According to phylogenetic analysis, this mouse cadherin-7 and its here presented human homologue are most likely the orthologues of Xenopus F-cadherin. These novel human genes, CDH7, CDH19, and CDH20, are localized on chromosome 18q22-q23, distal of both the gene CDH2 (18q11) encoding N-cadherin and the locus of the six desmosomal cadherin genes (18q12). Based on genetic linkage maps, this genomic region is close to the region to which Paget's disease was linked. Interestingly, the expression patterns of these three closely related cadherins are strikingly different.     

The L-isoaspartyl/D-aspartyl protein methyltransferase gene (PCMT1) maps to human chromosome 6q22.3-6q24 and the syntenic region of mouse chromosome 10.

We have mapped the genes for the human and mouse L-isoaspartyl/D-aspartyl protein carboxyl methyltransferase (EC 2.1.1.77) using cDNA probes. We determined that the human gene is present in chromosome 6 by Southern blot analysis of DNA from a panel of mouse-human somatic cell hybrids. In situ hybridization studies allowed us to confirm this identification and further localize the human gene (PCMT1) to the 6q22.3-6q24 region. By analyzing the presence of an EcoRI polymorphism in DNA from backcrosses of C57BL/6J and Mus spretus strains of mice, we localized the mouse gene (Pcmt-1) to chromosome 10, at a position 8.2 +/- 3.5 cM proximal to the Myb locus. This region of the mouse chromosome is homologous to the human 6q24 region.     

High-resolution linkage mapping for susceptibility genes in human polygenic disease: Insulin-dependent diabetes mellitus and chromosome 11q

Insulin-dependent diabetes mellitus (IDDM) has a complex pattern of genetic inheritance. In addition to genes mapping to the major histocompatibility complex (MHC), several lines of evidence point to the existence of other genetic susceptibility factors. Recent studies of the nonobese diabetic mouse (NOD) model of IDDM have suggested the presence, on mouse chromosome 9, of a susceptibility gene linked to the locus encoding the T-cell antigen, Thy-1. A region on human chromosome 11q is syntenic to this region on mouse chromosome 9. We have used a set of polymorphic DNA markers from chromosome 11q to investigate this region for linkage to a susceptibility gene in 81 multiplex diabetic pedigrees. The data were investigated by maximization of lod scores over genetic models and by multiple-locus affected-sib-pair analysis. We were able to exclude the presence of a susceptibility gene (location scores less than -2) throughout greater than 90% of the chromosome 11q homology region, under the assumption that the susceptibility factor would cause greater than 50% of affected sib pairs to share two alleles identical by descent. Theoretical estimates of the power to map susceptibility genes with a high-resolution map of linked markers in a candidate region were made, using HLA as a model locus. This result illustrates the feasibility that IDDM linkage studies using mapped sets of polymorphic DNA markers have, both for other areas of the genome in IDDM and for other polygenic diseases. The analytic approaches introduced here will be useful for affected-sib-pair studies of other complex phenotypes.     

Assignment of the gene for neuroendocrine protein 7B2 (SGNE1 locus) to mouse chromosome region 2[E3-F3] and to human chromosome region 15q11-q15

The gene for 7B2, a protein found in the secretory granules of neural and endocrine cells (gene symbol SGNE1) was localized to the E3-F3 region of mouse chromosome 2 and to the q11-q15 region of human chromosome 15. This was determined by in situ hybridization, using a mouse 7B2 cDNA and an intronic fragment of the corresponding human gene as probes. The respective locations of SGNE1 in the two species correlate with the conservation of loci between these subregions of mouse chromosome 2 and human chromosome 15. Clinically, the human SGNE1 DNA fragment may serve as a molecular probe of this locus in both the Prader-Willi and the Angelman syndromes, which are often accompanied by submicroscopic chromosomal deletions in the 15q11-15q13 region.     

Chromosomal localization of human genes required for G1 progression in mammalian cells

Specific probes derived from the human genes that complement the mutations of two independent temperature-sensitive (ts) mutants of the BHK-21 hamster cell line were used to determine the chromosomal locations of the loci in the human genome. The ts11 gene, which complements a mutation that blocks progression through the G1 phase of the cell cycle and which has now been identified as the structural gene for asparagine synthetase, is a member of a small gene/pseudogene family with four members. In a rodent-human somatic cell hybrid panel, the ts11 genomic locus from which the genomic probe derives segregates with human chromosome region 7cen----7q35, proximal to the TCR beta locus. In situ hybridization maps this locus more precisely to the q21-31 region of chromosome 7. Two other members of the gene family detected by the ts11 probe segregate concordantly with chromosome region 8pter----8q24 and chromosome region 21pter----21q22. Similar experiments using the same rodent-human hybrid panel conducted with a probe identifying the tsBN51 gene, which also encodes a function necessary for G1 progression, mapped this locus to human chromosome 8, proximal to the large amplification unit encompassing the c-myc gene of Colo320 cells. Chromosomal in situ hybridization of the tsBN51 probe confirmed the localization of this gene to chromosome 8, with the most likely location of the gene being 8q21.     

Absence of Linkage Between Human Obesity and the Mouse Agouti Homologous Region (20q11.2) or Other Markers Spanning Chromosome 20q

XU, WEIZHEN, DANIELLE R REED, YUAN DING AND R ARLEN PRICE. Absence of linkage between human obesity and the mouse agouti homologous region (20q11.2) or other markers spanning chromosome 20q. Obes Res. Mutant alleles of the agouti gene cause obesity in the mouse and the homologous gene in humans has been mapped to chromosome 20q11.2. An allelic variant of the agouti gene could account for obesity in humans and we tested this hypothesis by genotyping 210 sibling pairs from 45 families segregating an obesity phenotype. Using sibling pair linear regression analysis, evidence for linkage between obesity and markers flanking the agouti locus and other markers spanning chromosome 20q was assessed. We found no correlation between identity-by-descent at these markers and obesity differences within pairs. In the mouse, obesity caused by mutations of the agouti gene develops later in life, so a subset of families with adult-onset obesity were also tested for linkage, with negative results. Although it is not possible to exclude alleles of the agouti gene as a contributor to obesity in humans, the absence of positive linkage in this study suggests that either the agouti gene has small effects or the allele frequency is low.     

The gene for cystathionine beta-synthase (CBS) maps to the subtelomeric region on human chromosome 21q and to proximal mouse chromosome 17

The human gene for cystathionine beta-synthase (CBS), the enzyme deficient in classical homocystinuria, has been assigned to the subtelomeric region of band 21q22.3 by in situ hybridization of a rat cDNA probe to structurally rearranged chromosomes 21. The homologous locus in the mouse (Cbs) was mapped to the proximal half of mouse chromosome 17 by Southern analysis of Chinese hamster X mouse somatic cell hybrid DNA. Thus, CBS/Cbs and the gene for alpha A-crystalline (CRYA1/Crya-1 or Acry-1) form a conserved linkage group on human (HSA) chromosome region 21q22.3 and mouse (MMU) chromosome 17 region A-C. Features of Down syndrome (DS) caused by three copies of these genes should not be present in mice trisomic for MMU 16 that have been proposed as animal models for DS. Mice partially trisomic for MMU 16 or MMU 17 should allow gene-specific dissection of the trisomy 21 phenotype.