The 1993-94 Généthon human genetic linkage map

Assignment of Alu-repetitive sequences to large restriction fragments from human chromosomes 6 and 22

We have employed a pulsed field gel electrophoresis and Alu hybridization approach for identification of large restriction fragments on chromosome 6 and 22. This technique allows large portions of selected human chromosomes to be visualized as discrete hybridization signals. Somatic cell hybrid DNA which contains chromosome 6 or chromosome 22 was restricted with either Notl or Mlul. The restriction fragments were separated by pulsed field gel electrophoresis (PFGE) and hybridized against an Alu repetitive sequence (Blur 8). The hybridization signals result in a fingerprint-like pattern which is unique for each chromosome and each restriction enzyme. In addition, a continuous pattern of restriction fragments was demonstrated by gradually increasing puls times. This approach will also be suitable to analyze aberrant human chromosomes retained in somatic cell hybrids and can be used to analyze flow sorted human chromosomes. To this end, our method provides a valuable alternative to standard cytogenetic analysis.

Reciprocal translocation at 1p36.2/D1S160 in a neuroblastoma cell line: isolation of a YAC clone at the break

Band 1p36.1-1p36.2 is frequently involved in chromosomal aberrations of neuroblastoma cells, and therefore thought to harbour genetic information which may be involved in tumorigenesis. To map this putative neuroblastoma locus, we screened neuroblastoma cell lines for reciprocal translocations at 1p36.1-2 which may signal the site of an affected gene. We identified a reciprocal 1;15 translocation in cell line NGP by fluorescence in situ hybridisation (FISH). As a strategy to clone the translocation breakpoint, we isolated yeast artificial chromosomes (YACs) specific for loci at 1p36. Screening of cell line NGP by FISH identified a YAC, 1050 kbp in size, which hybridised to both derivative 1;15 and 15;1 chromosomes. We conclude that this YAC, which maps to D1S160, covers the break. This chromosomal position is within the smallest region of overlap (SRO) found in neuroblastoma tumours and within the region of a constitutional interstitial deletion of a neuroblastoma patient. The YAC we describe here should serve as a DNA source for gene cloning approaches towards the isolation of candidates for the putative neuroblastoma suppressor gene.

Linkage disequilibrium mapping of a type 1 diabetes susceptibility gene (IDDM7) to chromosome 2q31-q33

The role of human chromosome 2 in type 1 diabetes was evaluated by analysing linkage and linkage disequilibrium at 21 microsatellite marker loci, using 348 affected sibpair families and 107 simplex families. The microsatellite D2S152 was linked to, and associated with, disease in families from three different populations. Our evidence localizes a new diabetes susceptibility gene, IDDM7, to within two centiMorgans of D2S152. This places it in a region of chromosome 2q that shows conserved synteny with the region of mouse chromosome 1 containing the murine type 1 diabetes gene, Idd5. These results demonstrate the utility of polymorphic microsatellites for linkage disequilibrium mapping of genes for complex diseases.

Evidence for a major gene (RP10) for autosomal dominant retinitis pigmentosa on chromosome 7q: linkage mapping in a second, unrelated family

Retinitis pigmentosa is a genetically heterogeneous form of retinal degeneration, which has X-linked, autosomal recessive and autosomal dominant forms. The disease genes in families with autosomal dominant retinitis pigmentosa (adRP) have been linked to six loci, on 3q, 6p, 7p, 7q, 8q and 19q. In a large American family with late-onset adRP, microsatellite markers were used to test for linkage to the loci on 3q, 6p, 7p, and 8q. Linkage was found to 7q using the marker D7S480. Additional microsatellite markers from 7q were then tested. In total, five markers, D7S480, D7S514, D7S633, D7S650 and D7S677, show statistically significant evidence for linkage in this family, with a maximum two-point lod score of 5.3 at 0% recombination from D7S514. These results confirm an earlier report of linkage to an adRP locus (RP10) in an unrelated family of Spanish origin and indicate that RP10 may be a significant gene for inherited retinal degeneration. In addition, we used recently reported microsatellite markers from 7q to refine the linkage map of the RP10 locus.

A mutation in the alpha tropomyosin gene TPM3 associated with autosomal dominant nemaline myopathy

Nemaline myopathies are diseases characterized by the presence in muscle fibres of pathognomonic rod bodies. These are composed largely of alpha-actinin and actin. We have identified a missense mutation in the alpha-tropomyosin gene, TPM3, which segregates completely with the disease in a family whose autosomal dominant nemaline myopathy we had previously localized to chromosome 1p13-q25. The mutation substitutes an arginine residue for a highly conserved methionine in a putative actin-binding site near the N terminus of the alpha-tropomyosin. The mutation may strengthen tropomyosin - actin binding, leading to rod body formation, by adding a further basic residue to the postulated actin-binding motif.

Genetic and physical mapping of five novel microsatellite markers on human Xp21.1-p11.22

Five polymorphic CA-dinucleotide repeats, identified in cosmids from the short arm of the human X chromosome, have been characterized and localized to Xp21.1 (DXS572), Xp11.4 (DXS556, DXS574), and Xp11.22-p11.23 (DXS722, DXS573). Genetic mapping with respect to five reference markers that include the gene for CGD (CYBB in Xp21.1), complemented by physical mapping information, has indicated the order tel-DXS572-CYBB-DXS1110-DXS556-DXS574-D XS7-DXS426-DXS722-DXS573-DXS255-cen.

Peripherin gene is linked to keratin 18 gene on human chromosome 12

Peripherin is a neuron-specific intermediate filament (IF) protein, found primarily in phylogenetically old regions of the nervous system. Whereas other neuronal IF genes have only two to three introns and are scattered in the genome, the peripherin gene (PRPH) has a complex intron-exon structure like nonneuronal IF genes that are clustered in tandem arrays, e.g., those encoding the keratins. We used a cosmid containing the human peripherin gene (PRPH) to determine its chromosomal location in relationship to nonneuronal IF genes. Using a rodent-human mapping panel, we localized the PRPH gene to human chromosome 12. Since a cluster of keratin genes maps to 12q12-13, polymorphic markers were developed for PRPH and for one of the keratin genes presumed to be in the cluster, keratin 18 (KRT18). Both markers were typed in CEPH reference families. Pairwise and multipoint analyses of the CEPH data revealed that KRT18 is tightly linked to DNA markers D12S4, D12S22, D12S90, D12S96 and D12S103, which lie between D12S18 and D12S8, with odds greater than 1000:1. These markers are physically located at 12q11-13, thus supporting the fine localization of KRT18 in or near the group of type II keratins in this region. Furthermore, linkage analysis showed that the peripherin gene (PRPH) is tightly linked to KRT18 (Z = 15.73, theta = 0.013), and therefore appears to be in close proximity to the cluster.

A progressive early onset cataract gene maps to human chromosome 17q24

Cerulean cataract is an autosomal dominant, early onset, progressive cataract characterized by blue or white opacifications in the nucleus and cortex of the lens. A large four-generation pedigree in which cerulean cataract segregates was studied for linkage analysis. A genome wide search was undertaken after the plausible candidate genes were excluded and the cerulean cataract phenotype was mapped to chromosome 17q24. The three markers closest to the disease gene are D17S802 (Z)(theta) = 9.46 at (theta) = 0.085), D17S836 (Z(theta) = 5.26 at (theta) = 0.031) and AFMa238yb5 (Z(theta) = 7.11 at (theta) = 0.032). Multipoint linkage analyses yielded a maximum lod score of Z(theta) = 13.71, placing the cerulean cataract gene between D17S802 and D17S836 at (theta) = 0.048 and (theta) = 0.013, respectively.

Hereditary multi-infarct dementia unlinked to chromosome 19q12 in a large Scottish pedigree: evidence of probable locus heterogeneity

Hereditary multi-infarct dementia is a rare autosomal dominant disorder that predominantly affects the cerebral white matter. A locus was recently mapped in French pedigrees to chromosome 19q12. We have examined a large Scottish pedigree with neuropathologically confirmed hereditary multi-infarct dementia using polymorphic DNA markers spanning the 19q12 region and found no evidence of linkage. This suggests that, as in familial Alzheimer's disease, there is more than one locus.

The CEPH consortium linkage map of human chromosome 16

A Centre d'Etude du Polymorphisme Humain (CEPH) consortium map of human chromosome 16 has been constructed. The map contains 158 loci defined by 191 different probe/restriction enzyme combinations or primer pairs. The marker genotypes, contributed by 9 collaborating laboratories, originated from the CEPH families DNA. A total of 60 loci, with an average heterozygosity of 68%, have been placed on the framework genetic map. The genetic map contains 7 genes. The length of the sex-averaged map is 165 cM, with a mean genetic distance between loci of 2.8 cM; the median distance between markers is 2.0 cM. The male map length is 136 cM, and the female map length is 197 cM. The map covers virtually the entire chromosome, from D16S85, within 170 to 430 kb of the 16p telomere, to D16S303 at 16qter. The markers included in the linkage map have been physically mapped on a partial human chromosome 16 somatic cell hybrid panel, thus anchoring the genetic map to the cytogenetic-based physical map.

Physical and genetic localization of a Shab subfamily potassium channel (KCNB1) gene to chromosomal region 20q13.2

A human delayed rectifier K+ channel gene has been localized to the long arm of human chromosome 20q13.2 by fluorescence in situ hybridization of genomic P1 clones from this locus. A polymorphic (GA) microsatellite repeat was identified in one of the P1 clones. The new SSR marker (D20S436) was genotyped in four CEPH pedigrees. Two-point linkage analysis indicated linkage of this marker to a PCR marker, D20S109, with a maximum lod score of 9.32 at theta = 0.001. The assignment of this K+ channel gene to 20q13.2 eliminates it as a candidate for the gene associated with benign familial neonatal convulsions (BFNC), which has been localized to 20q13.3. Genetically, the K+ channel gene maps more than 30 cM proximal to the BFNC locus.

A missense mutation of the endothelin-B receptor gene in multigenic Hirschsprung's disease

Hirschsprung's disease (HSCR) is characterized by an absence of enteric ganglia in the distal colon and a failure of innervation in the gastrointestinal tract. We recently mapped a recessive susceptibility locus (HSCR2) to human chromosome 13q22, which we now demonstrate to be the endothelin-B receptor gene (EDNRB). We identified in HSCR patients a G-->T missense mutation in EDNRB exon 4 that substitutes the highly conserved Trp-276 residue in the fifth transmembrane helix of the G protein-coupled receptor with a Cys residue (W276C). The mutant W276C receptor exhibited a partial impairment of ligand-induced Ca2+ transient levels in transfected cells. The mutation is dosage sensitive, in that W276C homozygotes and heterozygotes have a 74% and a 21% risk, respectively, of developing HSCR. Genotype analysis of patients in a Mennonite pedigree shows HSCR to be a multigenic disorder.

Initial report of a genome search for the affective disorder predisposition gene in the old order Amish pedigrees: chromosomes 1 and 11

Family data have suggested that some forms of major affective disorder are genetic. Certain of the Old Order Amish pedigrees have a familial form of the disease. In this report we present the results of genetic analyses under autosomal dominant mode of transmission with reduced penetrance and three different disease hierarchies. The pedigrees were genotyped with 28 markers from chromosome 1 and 23 markers from chromosomes 11. None of the markers result in a significantly positive lod score.

The Sjögren-Larsson syndrome gene is close to D17S805 as determined by linkage analysis and allelic association

Sjögren-Larsson Syndrome (SLS) is characterized by congenital ichthyosis, spastic dior tetraplegia and mental retardation. It is an autosomal recessive trait that is frequent in the northern part of Sweden. Based on linkage analysis and allelic association, the disorder has now been mapped to chromosome 17. Meiotic recombinations suggest that the gene is flanked by D17S805 on the centromeric and D17S783, D17S959, D17S842 and D17S925 on the telomeric side. These markers map to the same location in reference pedigrees. Strong allelic association (chi-square 60.28, p < 0.0003) to D17S805 suggests that the mutation is located close to this marker.

Mapping a gene for Noonan syndrome to the long arm of chromosome 12

Noonan syndrome is characterized by typical facies, short stature and congenital cardiac defects. Approximately half of all cases are sporadic, but autosomal dominant inheritance with variable expression is well established. We have performed a genome-wide linkage analysis in a large Dutch kindred with autosomal dominant Noonan syndrome, and localized the Noonan syndrome gene to chromosome 12 (Zmax = 4.04 at 0 = 0.0). Linkage analysis using chromosome 12 markers in 20 smaller, two-generation families gave Zmax = 2.89 at 0 = 0.07, but haplotype analysis showed non-linkage in one family. These data imply that a gene for Noonan syndrome is located on chromosome 12q, between D12S84 and D12S366.

Genome screening by searching for shared segments: mapping a gene for benign recurrent intrahepatic cholestasis

It is now feasible to map disease genes by screening the genome for linkage disequilibrium between the disease and marker alleles. This report presents the first application of this approach for a previously unmapped locus. A gene for benign recurrent intrahepatic cholestasis (BRIC) was mapped to chromosome 18 by searching for chromosome segments shared by only three distantly related patients. The screening results were confirmed by identifying an extended haplotype conserved between the patients. Probability calculations indicate that such segment sharing is unlikely to arise by chance. Searching the genome for segments shared by patients is a powerful empirical method for mapping disease genes. Computer simulations suggest that, in appropriate populations, the approach may be used to localize genes for common diseases.

Genetics of haemochromatosis

This review is largely concerned with the frequency of genetic haemochromatosis (GH) and attempts to find the gene responsible. Studies of disease prevalence are reviewed along with the association of GH with other inherited disorders. The high prevalence of the disorder found in a number of surveys of populations of European origin along with the relatively few patients presenting with the clinical features of the advanced disease remains a paradox. The tight linkage between HLA-A and GH has been known since 1975 but it has not been possible to distinguish between a telomeric or centromeric location for the gene (HFE) relative to HLA-A. The recent explosion in detailed knowledge of the genetic map of the region telomeric of HLA-A on chromosome 6p has made it possible to examine new genetic markers. The very strong association between GH and D6S105-8 suggests a gene location telomeric to HLA-A. The lack of a precise location, and uncertainty about either the primary biochemical abnormality or the tissues involved has delayed the identification of the gene but expressed genes in the region around HLA-A are now being isolated and tested.

Comparative genetic mapping for the identification of novel diagnostic and therapeutic targets

The past year has seen significant advances in the genetic mapping of human and mouse genomes, with the publication of the most detailed and informative genetic maps compiled to date. These maps, together with those for several other species, provide a wealth of information for comparative mapping, with a view to identifying new human disease genes.

Loss of the wild type MLH1 gene is a feature of hereditary nonpolyposis colorectal cancer

The mechanism by which germline mutations of DNA mismatch repair genes cause susceptibility to tumour formation is not yet understood. Studies in vitro indicate that heterozygosity for these mutations, unlike homozygosity, does not affect mismatch repair. Surprisingly, no loss of heterozygosity at the predisposing loci has so far been described in hereditary nonpolyposis colorectal cancers. Here, we show that loss of heterozygosity (LOH) of markers within or adjacent to the MLH1 gene on chromosome 3p occurs nonrandomly in tumours from members of families in which the disease phenotype cosegregates with MLH1. In every informative case, the loss affects the wild type allele. These results suggest that DNA mismatch repair genes resemble tumour suppressor genes in that two hits are required to cause a phenotypic effect.

Comparative genome mapping in mammals

The mammals all have similar amounts of DNA, usually distributed over 40-60 chromosomes. Most of the differences in karyotype are related to fixation of less than 100 reciprocal translocations which have occurred over less than 100 million years. This allows the genome mapping of the main laboratory and farmyard species to help, and to be helped by, mapping of the human genome.

Simple sequences

Simple sequences (or microsatellites) are stretches of monotonous repetitions of short (1-5bp) nucleotide motifs that are distributed across the whole genome in eukaryotes. They are probably generated by slippage during replication and their primary mutation rate seems to be controlled predominantly by the efficiency of the mismatch repair system. Although most mutations in simple sequence loci appear to be neutral, some mutations in particular stretches have been implicated as having a role in human genetic diseases.

Liddle's syndrome: heritable human hypertension caused by mutations in the beta subunit of the epithelial sodium channel

Liddle's syndrome (pseudoaldosteronism) is an autosomal dominant form of human hypertension characterized by a constellation of findings suggesting constitutive activation of the amiloride-sensitive distal renal epithelial sodium channel. We demonstrate complete linkage of the gene encoding the beta subunit of the epithelial sodium channel to Liddle's syndrome in Liddle's original kindred. Analysis of this gene reveals a premature stop codon that truncates the cytoplasmic carboxyl terminus of the encoded protein in affected subjects. Analysis of subjects with Liddle's syndrome from four additional kindreds demonstrates either premature termination or frameshift mutations in this same carboxy-terminal domain in all four. These findings demonstrate that Liddle's syndrome is caused by mutations in the beta subunit of the epithelial sodium channel and have implications for the regulation of this epithelial ion channel as well as blood pressure homeostasis.

A functional "knockout" of human keratin 14

The importance of keratins and other intermediate filaments in the maintenance of tissue structure is emphasized by the discovery that many hereditary skin-blistering diseases are caused by mutations in keratin genes. Here, we describe a situation in which keratin 14 (K14) is missing altogether in the epidermis: A homozygous 2-nucleotide deletion in exon I of the K14 gene causes premature termination of the mRNA transcripts upstream from the start of the rod domain and results in a K14 null phenotype. In this individual no keratin intermediate filaments are visible in basal epidermal cells, although filaments are present in the upper layers of the epidermis. No compensating keratin expression is detected in vivo, and K14 mRNA is down-regulated. The individual, diagnosed as Köbner (generalized) EBS, suffers from severe widespread keratinocyte fragility and blistering at many body sites, but although the phenotype is severe, it is not lethal. This K14-/- phenotype confirms that only one K14 gene is expressed in human epidermis and provides an important model system for examining the interdependence of different keratin filament systems and their associated structures in the skin.

Molecular genetic methods for mapping disease genes

Recent technological enhancements in molecular genetics have significantly improved our ability to locate disease genes by linkage analysis. Despite the introduction of molecular methods such as PCR and the discovery of highly polymorphic SSRs, genotyping is still rate-limiting for localizing disease genes by linkage. These methods have been, until recently, highly technical, time-consuming, and expensive. The challenge of mapping the major genes that render one susceptible to environmentally initiated lung disorders such as asthma will require efficient and highly accurate methods of genotyping. We have shown that genotyping by semi-automated fluorescence-based techniques is both highly accurate and efficient. These methods may improve productivity by more than an order of magnitude and can be easily adapted to most linkage studies.

Fine mapping of the Darier's disease locus on chromosome 12q

Darier's disease (DD) is an autosomal dominant genodermatosis characterized by epidermal acantholysis and dyskeratosis. We have performed genetic linkage studies in 10 families with DD (34 affected) by analyzing 14 polymorphic microsatellite markers. Our results confirm recent reports mapping the DD gene to chromosome 12q23-q24.1. Haplotype analysis of recombinant chromosomes in our families, along with previously reported data, narrow the location of the DD gene to a 5 cM interval flanked by the loci D12S354 and D12S84/D12S105. This localization allowed exclusion of two known genes, PLA2A and PAH, as candidate loci for DD. Three other gene loci (PPP1C, PMCH, PMCA1), mapping in 12q21-q24, remain potential candidates.

Spinocerebellar ataxia type 5 in a family descended from the grandparents of President Lincoln maps to chromosome 11

Autosomal dominant ataxias are a genetically heterogeneous group of disorders for which spinocerebellar ataxia (SCA) loci on chromosomes 6p, 12q, 14q and 16q have been reported. We have examined 170 individuals (56 of whom were affected) from a previously unreported ten-generation kindred with a dominant ataxia that is clinically and genetically distinct from those previously mapped. The family has two major branches which both descend from the paternal grandparents of President Abraham Lincoln. Among those examined, 56 individuals have a generally non-life threatening cerebellar ataxia. Disease onset varies from 10-68 years and anticipation is evident. We have mapped this gene, spinocerebellar ataxia type 5 (SCA5), to the centromeric region of chromosome 11.

Two long QT syndrome loci map to chromosomes 3 and 7 with evidence for further heterogeneity

Cardiac arrhythmias cause sudden death in 300,000 United States citizens every year. In this study, we describe two new loci for an inherited cardiac arrhythmia, long QT syndrome (LQT). In 1991 we reported linkage of LQT to chromosome 11p15.5. In this study we demonstrate further linkage to D7S483 in nine families with a combined lod score of 19.41 and to D3S1100 in three families with a combined score of 6.72. These findings localize major LQT genes to chromosomes 7q35-36 and 3p21-24, respectively. Linkage to any known locus was excluded in three families indicating that additional heterogeneity exists. Proteins encoded by different LQT genes may interact to modulate cardiac repolarization and arrhythmia risk.

A comprehensive human linkage map with centimorgan density. Cooperative Human Linkage Center (CHLC)

In the last few years there have been rapid advances in developing genetic maps for humans, greatly enhancing our ability to localize and identify genes for inherited disorders. Through the collaborative efforts of three large groups generating microsatellite markers and the efforts of the 110 CEPH collaborators, a comprehensive human linkage map is presented here. It consists of 5840 loci, of which 970 are uniquely ordered, covering 4000 centimorgans on the sex-averaged map. Of these loci, 3617 are polymerase chain reaction-formatted short tandem repeat polymorphisms, and another 427 are genes. The map has markers at an average density of 0.7 centimorgan, providing a resource for ready transference to physical maps and achieving one of the first goals of the Human Genome Project--a comprehensive, high-density genetic map.

Localization of a breast cancer susceptibility gene, BRCA2, to chromosome 13q12-13

A small proportion of breast cancer, in particular those cases arising at a young age, is due to the inheritance of dominant susceptibility genes conferring a high risk of the disease. A genomic linkage search was performed with 15 high-risk breast cancer families that were unlinked to the BRCA1 locus on chromosome 17q21. This analysis localized a second breast cancer susceptibility locus, BRCA2, to a 6-centimorgan interval on chromosome 13q12-13. Preliminary evidence suggests that BRCA2 confers a high risk of breast cancer but, unlike BRCA1, does not confer a substantially elevated risk of ovarian cancer.

A genome-wide search for human type 1 diabetes susceptibility genes

We have searched the human genome for genes that predispose to type 1 (insulin-dependent) diabetes mellitus using semi-automated fluorescence-based technology and linkage analysis. In addition to IDDM1 (in the major histocompatibility complex on chromosome 6p21) and IDDM2 (in the insulin gene region on chromosome 11p15), eighteen different chromosome regions showed some positive evidence of linkage to disease. Linkages to chromosomes 11q (IDDM4) and 6q (IDDM5) were confirmed by replication, and chromosome 18 may encode a fifth disease locus. There are probably no genes with large effects aside from IDDM1. Therefore polygenic inheritance is indicated, with a major locus at the major histocompatibility complex.

Genetic mapping of a susceptibility locus for insulin-dependent diabetes mellitus on chromosome 11q

Loci in the major histocompatibility complex (MHC) on chromosome 6 and the insulin (INS) region on chromosome 11 have been implicated in susceptibility to insulin-dependent diabetes mellitus (IDDM) through candidate gene investigations, but they may account for less than 50% of genetic risk for the disease. Genome-wide linkage studies have led to localization of more than 10 susceptibility loci for insulin-dependent diabetes in the non-obese diabetic (NOD) mouse and the BB rat. Similar studies are now possible in humans through the development of dense genetic maps of highly informative microsatellite loci obtained using polymerase chain reaction analysis. We have applied microsatellite markers from recent Généthon maps, and other highly informative markers, in a genome-wide linkage study in IDDM. Here we report evidence for the localization of a previously undetected susceptibility locus for IDDM in the region of the FGF3 gene on chromosome 11q. Our results shows the potential of genome-wide linkage studies to detect susceptibility loci in IDDM and other multifactorial disorders.

A radiation hybrid map of 506 STS markers spanning human chromosome 11

We present a high resolution radiation hybrid map of human chromosome 11 using 506 sequence tagged sites (STSs) scored on a panel of 86 radiation hybrids. The 506 STSs fall into 299 unique positions (average resolution of about 480 kilobases (kb)) that span the whole chromosome. A subset of 260 STSs (143 positions) form a framework map that has a resolution of approximately 1 megabase between adjacent positions and is ordered with odds of at least 1,000:1. The centromere was clearly defined with pericentric markers unambiguously assigned to the short or long arm. The map contains most genes (125) and expressed sequence tags (26) currently assigned to chromosome 11 and more than half of the STSs are polymorphic microsatellite loci. These markers and the map can be used for high resolution physical and genetic mapping.

Linkage of the gene for Wolfram syndrome to markers on the short arm of chromosome 4

Wolfram syndrome is an autosomal recessive disorder defined by the occurrence of diabetes mellitus and progressive bilateral optic atrophy. Wolfram syndrome homozygotes develop widespread nervous system abnormalities; in particular, they exhibit severe behavioural difficulties that often lead to suicide attempts or psychiatric hospitalizations. The Wolfram syndrome gene also predisposes heterozygous carriers to psychiatric disorders, and may contribute significantly to the overall burden of psychiatric illness. Based on a linkage analysis of 11 families segregating for this syndrome using microsatellite repeat polymorphisms throughout the human genome, we found the Wolfram syndrome gene to be linked to markers on the short arm of human chromosome 4, with Zmax = 6.46 at theta = 0.02 for marker D4S431.

Human artificial episomal chromosomes for cloning large DNA fragments in human cells

We have developed a human artificial episomal chromosome (HAEC) system, based on the latent replication origin of the large herpes Epstein-Barr virus, for the propagation and stable maintenance of DNA as circular minichromosomes in human cells. Individual HAECs carried human genomic inserts ranging from 60-330 kb and appeared genetically stable. An HAEC library of 1,500 independent clones carrying random human genomic fragments with average sizes of 150-200 kb was established and allowed recovery of the HAEC DNA. Our autologous HAEC system, with human DNA cloned directly in human cells, provides an important tool for functional study of large mammalian DNA regions and gene therapy.

Chromosome-specific microsatellite sets for fluorescence-based, semi-automated genome mapping

To facilitate large-scale genetic mapping of the human genome, we have developed chromosome-specific sets of microsatellite marker loci suitable for use with a fluorescence-based automated DNA fragment analyser. We present 254 dinucleotide repeat marker loci (80% from the Généthon genetic linkage map) arranged into 39 sets, covering all 22 autosomes and the X chromosome. The average distance between adjacent markers is 13 centiMorgans, and less than 4% of the genome lies more than 20 cM from the nearest marker. Each set of microsatellites consists of up to nine marker loci, with allele size ranges that do not overlap. We selected marker loci on the basis of their reliability in the polymerase chain reaction, polymorphism content, map position and the accuracy with which alleles can be scored automatically by the Genotyper program.

Cohen syndrome gene assigned to the long arm of chromosome 8 by linkage analysis

Cohen syndrome is an autosomal recessive disorder characterized by mental and motor retardation, short stature, microcephaly, several dysmorphic features, major ocular symptoms and granulocytopenia. Major research challenges are the confusing nosology and the pleiotropy of the gene. We report the mapping of a locus (CHS1) by linkage analysis in as few as four two-generation pedigrees with uniform clinical features. CHS1 was assigned to an interval of approximately 10 cM between D8S270 and D8S521. Our results provide a tool to a more accurate definition of Cohen syndrome(s) and a starting point for the positional cloning of CHS1.

A genetic map of the mouse with 4,006 simple sequence length polymorphisms

We have constructed a genetic map of the mouse genome containing 4,006 simple sequence length polymorphisms (SSLPs). The map provides an average spacing of 0.35 centiMorgans (cM) between markers, corresponding to about 750 kb. Approximately 90% of the genome lies within 1.1 cM of a marker and 99% lies within 2.2 cM. The markers have an average polymorphism rate of 50% in crosses between laboratory strains. The markers are distributed in a relatively uniform fashion across the genome, although some deviations from randomness can be detected. In particular, there is a significant underrepresentation of markers on the X chromosome. This map represents the two-thirds point toward our goal of developing a mouse genetic map containing 6,000 SSLPs.

Gene for familial psoriasis susceptibility mapped to the distal end of human chromosome 17q

A gene involved in psoriasis susceptibility was localized to the distal region of human chromosome 17q as a result of a genome-wide linkage analysis with polymorphic microsatellites and eight multiply affected psoriasis kindreds. In the family which showed the strongest evidence for linkage, the recombination fraction between a psoriasis susceptibility locus and D17S784 was 0.04 with a maximum two-point lod score of 5.33. There was also evidence for genetic heterogeneity and although none of the linked families showed any association with HLA-Cw6, two unlinked families showed weak levels of association. This study demonstrates that in some families, psoriasis susceptibility is due to variation at a single major genetic locus other than the human lymphocyte antigen locus.