Genetic linkage with chromosome 19 but not chromosome 17 in a family with myotonic dystrophy associated with hereditary motor and sensory neuropathy

We identified a large kindred that shows classical myotonic dystrophy (MyD), together with hereditary motor and sensory neuropathy (HMSN) in some individuals, and HMSN alone in others. A previous study of this family has shown cosegregation of the MyD and HMSN phenotypes with the Lutheran and secretor loci in some branches of the family, indicating linkage to chromosome 19. We reanalyzed this family with 2 recombinant DNA marker systems from the ApoC2 locus on chromosome 19. Our results demonstrate that all affected individuals have inherited a unique ApoC2 haplotype that was not found in their clinically and electrophysiologically normal sibs. We also obtained evidence against involvement of the HMSN I locus on chromosome 17. In this family, a moderately severe neuropathy may be the only clinical sign of MyD for many years. Our results are consistent with an unusual neuropathic mutation at the MyD gene. However, involvement of 2 closely linked genes (1 for MyD and the other for HMSN) can also explain our findings.

Cloning of a gene that is rearranged in patients with choroideraemia

Choroideraemia (tapetochoroidal dystrophy, TCD), a common form of X-linked blindness, is characterized by progressive dystrophy of the choroid, retinal pigment epithelium and retina. Previous studies have assigned the TCD gene to a small segment of the Xq21 band. By making use of reverse genetics strategies we have isolated eight overlapping complementary DNA clones from the same chromosomal region. The corresponding gene is expressed in retina, choroid and retinal pigment epithelium. The cDNAs encompass an open reading frame of 948 base pairs that is structurally altered in eight TCD patients with deletions, and in a female patient with a balanced translocation involving Xq21. These findings provide strong evidence that we have cloned the gene underlying choroideraemia. Elucidation of its function should provide new insights into the molecular mechanisms responsible for this disorder and other hereditary retinopathies.

Derivatives of somatic cell hybrids which carry the human gene locus for nephrogenic diabetes insipidus (NDI) express functional vasopressin renal V2-type receptors

The gene responsible for familial vasopressin-resistant nephrogenic diabetes insipidus (NDI) has been localized to a small region of the human X-chromosome (Xq28). A series of hamster lung fibroblast and mouse lymphocyte cell lines carrying fragments of the wild type human X-chromosome was analyzed for vasopressin renal-type V2 receptor expression, to test the hypothesis that the NDI locus may have identity with the V2 receptor gene. V2 receptor binding activity and induction of cAMP production in response to [Arg8] vasopressin (AVP) were exhibited by all cell lines carrying the wild type NDI locus, in contrast to control cell lines. AVP stimulation of cAMP production was concentration-dependent and could be almost completely inhibited by co-incubation with a V2-V1 receptor-specific antagonist. The V2-specific agonist [Mpa1,Val4,Sar7]AVP was as potent as AVP in inducing cAMP production by NDI-DNA-carrying cells, whereas no response was shown to other hormones such as calcitonin, oxytocin (less than 10(-8) M), isoproterenol, or an oxytocin-specific agonist. All results were consistent with the hypothesis that the V2 receptor gene co-localized with the NDI locus, supporting the view that the loci are one and the same.

Physical mapping of new DNA probes near the fragile X mutation (FRAXA) by using a panel of cell lines

The fragile X syndrome is a very common disorder, but there has been little progress toward isolating the fragile X mutation (FRAXA). We describe a panel of 14 somatic cell hybrid lines, lymphoblastoid cell lines, and peripheral lymphocytes with X-chromosome translocation or deletion breakpoints near FRAXA. The locations of the breakpoints were defined with 16 established probes between pX45d (DXS100) and St14-1 (DXS52). Seven of the cell lines had breakpoints between the probes RN1 (DXS369) and U6.2 (DXS304), which flank FRAXA at distances of 3-5 centimorgans. The panel of cell lines was used to localize 16 new DNA probes in this region. Six of the probes-VK16, VK18, VK23, VK24, VK37, and VK47--detected loci near FRAXA, and it was possible to order both the X-chromosome breakpoints and the probes in relation to FRAXA. The order of probes and loci near FRAXA is cen-RN1,VK24-VK47-VK23-VK16,FRAXA-++ +VK21A-VK18-IDS-VK37-U6.2-qter. The breakpoints near FRAXA are sufficiently close together that probes localized with this panel can be linked on a large-scale restriction map by pulsed-field gel electrophoresis. This panel of cell lines will be valuable in rapidly localizing other probes near FRAXA.

An NcoI restriction fragment length polymorphism at the human steroid sulphatase gene locus

The DNA diagnosis of X-linked recessive ichthyosis vulgaris (incidence: approx. 1 in 5000 males) can be complicated by the absence of restriction fragment length polymorphisms (RFLPs) in the STS (steroid sulphatase) gene. An RFLP sequence in NcoI-digested genomic DNA is reported, which it is hoped may prove helpful in diagnosis.

Derivation of clones from the choroideremia locus by preparative field inversion gel electrophoresis

By making use of preparative field inversion gel electrophoresis, we have constructed a lambda ZAP library that is highly enriched for sequences from the choroideremia locus. In vivo excision of pBluescript SK(-) constructs from lambda ZAP obviates the subcloning of DNA inserts and allows for rapid processing of several hundred recombinants. From a 625 kb Sfil fragment we isolated 7 clones that were physically mapped using microdeletions associated with the disease. One of these clones is located within, or just telomeric to, the choroideremia gene and detects two restriction fragment length polymorphisms (RFLPs). Another clone detects a RFLP which maps centromeric to the disease locus. Together these probes should improve the reliability of linkage analysis in choroideremia families and should pave the way for the isolation of the choroideremia gene.

Physical fine-mapping of a deletion spanning the Norrie gene

Norrie disease (ND), atrophia bulborum hereditaria, is caused by a gene defect on the proximal short arm of the X-chromosome. As shown by us and others, microdeletions spanning the DXS7 locus are not uncommon in this disorder, and there is recent evidence that, at least in some of the Norrie deletion patients, the monoamine oxidase (MAO) A and B genes are deleted as well. Molecular hybridization experiments with 19 cloned DNA fragments have enabled us to construct a preliminary long-range restriction map around DXS77, DXS7, MAO-A and MAO-B, and to localize the distal end point of an ND deletion between DXS77 and DXS7.

A multipoint linkage map around the locus for myotonic dystrophy on chromosome 19

Employing 16 polymorphic DNA markers as well as the chromosome 19 centromere heteromorphism, we have performed a genetic linkage study in 26 families with myotonic dystrophy. Fourteen of these markers had been assigned previously to one of five different intervals of the 19cen-19q13.2 segment by using somatic cell hybrids. For the long arm of chromosome 19, a genetic map that encompasses 9 polymorphic markers and the DM gene has been constructed. Our studies indicate that the DM and CKMM genes map distal to the ApoC2-ApoE gene cluster and to the anonymous polymorphic markers D19S15 and D19S16, but proximal to the D19S22 marker. The orientation of DM and CKMM remains to be determined.

Chromosomal jumping from the DXS165 locus allows molecular characterization of four microdeletions and a de novo chromosome X/13 translocation associated with choroideremia

Choroideremia (tapeto-choroidal dystrophy, TCD), an X chromosome-linked disorder of retina and choroid, causes progressive nightblindness and central blindness in affected males by the third to fourth decade of life. Recently, we have been able to map the TCD gene to a small region of overlap between five different, male-viable Xq21 deletions that were found in patients with TCD and other clinical features. Two families were identified in which classical, nonsyndromic TCD is associated with small interstitial deletions that are only detectable with probe p1bD5 (DXS165). To characterize these and two other deletions that were identified more recently, we have used the chromosome walking and jumping techniques to generate a set of five chromosomal-jumping clones flanking the DXS165 locus at various distances. With these clones, we could localize four of the eight deletion endpoints and the breakpoint on the X chromosome of a female with a de novo X/13 translocation and choroideremia. These studies assign the TCD gene, or part of it, to a DNA segment of only 15-20 kilobases.

Use of variable simple sequence motifs as genetic markers: application to study of myotonic dystrophy

Among the many classes of repetitive elements present in the human genome, the ubiquitous "simple sequence motifs" (SSMs) composed of [A]n, [TG]n, [AG]n or codon-tandem repeats form a major source of genetic variation. Here we report a detailed molecular-genetic study of a "variable simple sequence motif" (VSSM) in the apolipoprotein C2 (apoC2) gene, which maps to the 19q13.2 region in the vicinity of the myotonic dystrophy (DM) locus. By combining in vitro DNA-amplification using the polymerase chain reaction and high-resolution gel electrophoresis, we could demonstrate a high degree of allelic variation with at least ten alleles, which differ in the number of repeated [TG] or [AG] dinucleotide units. Similar results were found for the somatostatin I gene locus. To evaluate the usefulness of SSM-length polymorphisms as genetic markers, the apoC2-VSSM was employed for linkage analysis in DM families. Our results establish that the orientation of the apolipoprotein gene cluster on 19q is cenapoE-apoC2-ter and indicate that the many thousands of structurally similar VSSMs in the human genome represent a rich source of highly informative genetic and diagnostic markers.

The recombinant DNA revolution: implications for diagnosis and prevention of inherited disease

Since the introduction of DNA probes as diagnostic tags, closely linked markers have been detected for 18 of the 22 most common Mendelian defects which account for 75% of the morbidity and mortality in this group. Still, as tools for diagnosis and prevention, linked probes are not completely reliable because of occasional crossovers; moreover, this diagnostic approach is not possible for sporadic cases. Fortunately, some of these limitations can be overcome by using a new strategy, termed 'reverse genetics', which aims at the detection of the primary gene defect at the DNA level and should provide the clue to the elucidation of the corresponding biochemical defect which is mostly not understood. These studies should also improve the prospects for therapy, either conventional or through replacement of the defective gene. Furthermore, new techniques have been developed in the mouse that allow the detection of specific gene defects in preimplantation embryos. If combined with in vitro fertilization, similar techniques may provide an alternative to prenatal diagnosis in situations where therapeutic abortion is not considered acceptable.

EcoRI RFLP at 19q13.1 identified by the anonymous DNA sequence p58B18 [D19S32]

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MspI RFLP at 19q12-q13.1 identified by the anonymous DNA sequence p30B18 [D19S31]

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MspI RFLP at 19cen-q12 identified by the anonymous DNA sequence pPM17.4 [D19S29]

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TaqI RFLP at 19q13.1 identified by the anonymous DNA sequence p5B18 [D19S28]

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MspI RFLP at 19q12-q13.1 identified by the anonymous DNA sequence p20B18 [D19S30]

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Three-point linkage analysis using multiple DNA polymorphic markers in families with X-linked nephrogenic diabetes insipidus

The gene for X-linked nephrogenic diabetes insipidus (NDI), a disorder which, if untreated, causes severe dehydration, mental retardation, and possibly death in affected males, has been mapped recently to the Xq28 band through demonstration of linkage to the DX552 locus and other DNA markers (N. Knoers et al., 1987, Cytogenet. Cell Genet. 46:640; M. Kambouris et al., 1987, Cytogenet. Cell Genet. 46:636). Linkage studies in 11 families with NDI have enabled us to map the NDI gene between closely linked flanking markers in the Xq28 region and to obtain the following gene order: centromere-F9-DXS98-F8/CBD,CBP-DXS52/NDI-DXS134- telomere. These results have implications for presymptomatic and prenatal diagnosis of NDI and should also improve the prospects for identifying the fundamental gene defect underlying this disorder.

Myotonic dystrophy is closely linked to the gene for muscle-type creatine kinase (CKMM)

We have studied genetic linkage between the gene for creatine kinase muscle type (CKMM) and the gene for myotonic dystrophy (DM). In a panel of 65 myotonic dystrophy families from Canada and the Netherlands, a maximum lod score (Zmax) of 22.8 at a recombination frequency (theta) of 0.03 was obtained. Tight linkage was also demonstrated for CKMM and the gene for apolipoprotein C2 (ApoC2). This establishes CKMM as a useful marker for myotonic dystrophy.

Physical fine mapping of the choroideremia locus using Xq21 deletions associated with complex syndromes

Characterization of several male-viable deletions and duplications with 20 random DNA probes has enabled us to subdivide the Xq21 region into seven discernible intervals. Almost all of the deletions spanning part of Xq21 are associated with choroideremia and mental retardation, with deafness being another common feature. The gene locus for choroideremia was assigned to interval 3 spanning the loci DXS95, DXS165, and DXS233. Genes for X-linked deafness and mental retardation were tentatively assigned to interval 2. Deletions of intervals 4 through 7 were not associated with any clinical abnormality. We have constructed a preliminary long-range restriction map of intervals 2 and 3 using field-inversion gel electrophoresis. The DXS232, DXS121, and DXS233 loci are located on the same SfiI fragment, whereas the DXS165 and DXS95 loci could not be linked to this cluster using SfiI and SalI.

The gene for X-linked progressive mixed deafness with perilymphatic gusher during stapes surgery (DFN3) is linked to PGK

A linkage analysis has been performed in a large Dutch kindred with progressive mixed deafness with perilymphatic gusher during stapes surgery (DFN3) using a panel of X-chromosomal RFLPs. Tight linkage (zmax = 3.07 at 0 = theta = 0.00) was demonstrated with the locus for phosphoglycerate kinase (PGK), which is located at Xq13. Tight linkage was excluded for DXS9 (probe RC8) and DXS41 (probe 99.6) on Xp and for blood clotting factor 9 (FIX) on distal Xq. Deafness is one of the predominant clinical features in males with deletions of the Xq21 band. Our results suggest that this association may be due to involvement of the DFN3 gene.

The human lactase-phlorizin hydrolase gene is located on chromosome 2

The lactase-phlorizin hydrolase gene was assigned to chromosome 2 by analysis of Southern blots of DNA from a panel of human-rodent cell hybrids containing characteristic sets of human chromosomes The hybridization probe used was a recently isolated cDNA clone of the human lactase-phlorizin hydrolase gene.

Assignment of the human aminopeptidase N (peptidase E) gene to chromosome 15q13-qter

The gene for aminopeptidase N (EC 3.4.11.2) has been located on the human chromosome 15q13-qter using HindIII-cleaved DNA from a panel of hybrids between rodent and human cells. The Southern blots were probed by the 5'-EcoRI fragment of the recently cloned human aminopeptidase N cDNA.

Localization of the gene for X-linked Alport's syndrome

X-chromosomal DNA probes defining various polymorphic DNA markers were used to study genetic linkage in three families with Alport's syndrome. With the DXS17 marker, only a single cross-over was observed in 26 informative meioses, and evidence for linkage was also obtained with the DXS11 marker. These data localize the gene for the X-linked form of Alport's syndrome to the middle of the long arm of the X chromosome.

Molecular analysis of male-viable deletions and duplications allows ordering of 52 DNA probes on proximal Xq

While performing a systematic search for chromosomal microdeletions in patients with clinically complex X-linked syndromes, we have observed that large male-viable deletions and duplications are clustered in heterochromatic regions of the X chromosome. Apart from the Xp21 band, where numerous deletions have been found that encompass the Duchenne muscular dystrophy gene, an increasing number of deletions and duplications have been observed that span (part of) the Xq21 segment. To refine the molecular and genetic map of this region, we have employed 52 cloned single-copy DNA sequences from the Xcen-q22 segment to characterize two partly overlapping tandem duplications and two interstitial deletions on the proximal long arm of the human X chromosome. Together with a panel of somatic cell hybrids that had been described earlier, these four rearrangements enabled us to order the 52 probes into nine different groups and to narrow the regional assignment of several genes, including those for tapetochoroidal dystrophy and anhidrotic ectodermal dysplasia.

Identification of apolipoprotein E polymorphism by using synthetic oligonucleotides

A procedure based on selective hybridization with allele-specific oligonucleotides was developed for typing apolipoprotein E variants from human genomic DNAs. Two sets of oligonucleotides were synthesized and used to discriminate either between epsilon 3 and epsilon 4 alleles or between epsilon 3 and epsilon 2 alleles. Combination of the allele-specific oligonucleotide hybridization with the method for in vitro DNA amplification (Polymerase Chain Reaction) Saiki, R. K. et al. 1985. Science, 230: 1350-1354) (1) dramatically improved the sensitivity and the reliability of the procedure. Adaptation of a simple strategy involving direct cloning and DNA sequencing of in vitro amplified DNA enables rapid identification of any mutation within the apoE gene area encoding the receptor binding domain.

Tight linkage between myotonic dystrophy and apolipoprotein E genes revealed with allele-specific oligonucleotides

In 16 families with myotonic dystrophy (DM) a novel approach based on use of allele-specific oligonucleotides has been employed to study the linkage relationship between the apolipoprotein E (APOE) gene and DM. Synthetic oligonucleotides, designed to discriminate between APOE alleles epsilon 3 and epsilon 4, enabled us to distinguish heterozygous carriers in a hybridization assay. In a subset of families, the relevant segment of the APOE gene was enzymatically amplified to increase the sensitivity of the method. For DM and APOE, a maximum lod score (zmax of 7.47 was obtained at a recombination frequency (theta) of 0.047 (male theta = female theta). No recombination (maximum lod score of 5.61 at theta = 0.0) was found between APOE and the apolipoprotein CII (APOC2) gene. These results suggest that, in addition to APOC2, APOE is a useful marker for presymptomatic DM diagnosis.

Nephrogenic diabetes insipidus: close linkage with markers from the distal long arm of the human X chromosome

Ten families with nephrogenic diabetes insipidus (NDI) have been analysed for restriction fragment length polymorphisms (RFLPs). A search for linkage was performed using various chromosome-specific single-copy DNA probes of known regional assignment to the human X chromosome. Close linkage was found between the disease locus and the markers DXS52, DXS15, DXS134 and the F8 gene. This result assigns the NDI gene to the subtelomeric region of the long arm of the X chromosome. The regional localization of the gene by the identification of closely linked markers should have repercussions for genetic counselling and prevention in NDI families.

The poliovirus sensitivity (PVS) gene is on chromosome 19q12----q13.2

Sensitivity to nonmodified poliovirus infection is an autosomal dominant trait, specific to primates. The gene for poliovirus sensitivity (PVS) is encoded on human chromosome 19. In order to sublocalize the PVS gene, we infected rodent-human hybrid cell lines that divide human chromosome 19 into four regions with poliovirus 1 and/or 3. When infected, these hybrid cell lines showed the typical cytopathic effect of poliovirus infection only if they contained 19q12----q13.2 as the smallest region of overlap. Appropriate negative and positive controls were used. PVS may be of relevance to myotonic dystrophy (DM) and the inherited motor neuron diseases: to DM because it localizes to the same region of chromosome 19 and to the inherited motor neuron diseases because it encodes a cell-surface receptor expressed on motor neurons.

Linkage of X-linked nephrogenic diabetes insipidus with DXS52, a polymorphic DNA marker

In five families with X-linked nephrogenic diabetes insipidus (NDI), linkage studies with the DNA marker DXS52, defined by probe St14, have shown no recombination with a maximum combined lod score of 6.40. These results assign the NDI gene to the subtelomeric region of the X chromosome long arm. This finding should facilitate identification of carriers and should also be helpful in finding the NDI gene itself.

Isolation and characterization of alphoid DNA sequences specific for the pericentric regions of chromosomes 4, 5, 9, and 19

We have cloned and characterized two distinct types of alphoid DNA elements. Probe pG-Xba 11/340 was obtained by random cloning of human satellite DNA and contains two basic units with overall 88% homology to the 171-bp consensus alphoid sequence. pG-Xba 11/340-like elements are represented about 2,000-4,000 times in the haploid genome and, by in situ hybridization, are found exclusively at the primary constrictions of chromosomes 4 and 9. Probe pG-A16 was cloned from a chromosome 19-specific cosmid library and represents a 2.25-kb higher-order DNA element which is present at roughly 75-150 copies per haploid genome and which hybridizes to the centromeres of chromosomes 5 and 19. Using the pG-A16 probe, further genetic and physical dissection of the central area of chromosome 19 can be envisaged.

Deletion of the DXS165 locus in patients with classical choroideremia

Using various probes from the Xq21 region which is known to carry the choroideremia (tapetochoroideal dystrophy, TCD) locus, we have screened the DNAs from eight unrelated male choroidermia patients for microdeletions. In two of these patients, but not in any of 45 males tested as controls, lack of hybridization signals with probe plbD5 suggested a deletion encompassing the DXS165 locus and (part of) the TCD gene. Absence of additional clinical features in these patients and the fact that two closely linked, and probably flanking, TCD markers (DXYS1 and DXS72) are not deleted may indicate that the physical distance between the DXS165 locus and the TCD gene is small.

EcoRI RFLP at 19 cen-q13.2 identified by the anonymous DNA sequence pPM6.7 (D19S18)

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An interstitial duplication of the X chromosome in a male allows physical fine mapping of probes from the Xq13-q22 region

An insertional translocation into the proximal long arm of the X chromosome in a boy showing muscular hypotony, growth retardation, psychomotor retardation, cryptorchidism, and Pelizaeus-Merzbacher disease (PMD) was identified as a duplication of the Xq21-q22 segment by employing DNA probes. With densitometric scanning for quantitation of hybridization signals, 15 Xq probes were assigned to the duplicated region. Analysis of the duplication allowed us to dissect the X-Y homologous region physically at Xq21 and to refine the assignments of the loci for DXYS5, DXYS12, DXYS13, DXS94, DXS95, DXS96, DXS111, and DXS211. Furthermore, we demonstrated the presence of two different DXYS13 and DXS17 alleles in genomic DNA of our patient, suggesting that the duplication resulted from a meiotic recombination event involving the two maternal X chromosomes.

Physical mapping of genes and sequences at the end of the human X chromosome short arm

Human-rodent somatic cell hybrids containing deleted and translocated human X chromosomes have been used to map genes and sequences in and around the pseudoautosomal region. The following order was found: (DXS69, DXS70, DXS143)-(DXS31, STS)-MIC2. This order is consistent with the known inheritance patterns of DXS31, STS and MIC2. Assuming that the translocations and deletions we have studied are not complex rearrangements, we conclude that the pseudoautosomal region consists of less than 5 X 10(6) bp of DNA.

A locus at 19cen-19q13.2 (D19S15) containing three RFLPs linked to myotonic dystrophy (DM) is recognized by probe pJSB6

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Three-point linkage analysis employing C3 and 19cen markers assigns the myotonic dystrophy gene to 19q

In seven large families with myotonic dystrophy (DM) comprising 102 individuals, linkage studies were performed employing restriction fragment length polymorphisms in the complement component 3 gene and the 19cen C banding heteromorphism as genetic markers. Three-point linkage analysis excludes DM from the 19cen-C3 segment and strongly supports its assignment to the proximal long arm of chromosome 19.

Localization of MIC5 to the region between HPRT and G6PD on the human X chromosome

The X-linked gene, MIC5, encodes a human cell-surface antigen, R1. We have assigned MIC5 to the region between HPRT and G6PD on the long arm of the X chromosome. Regional localization was based on the pattern of reactivity of the R1 monoclonal antibody with human-rodent somatic cell hybrids which contained different fragments of the human X chromosome.

Regional localisation of X chromosome short arm probes

Nine human X chromosome-specific clones have been isolated by screening an X-chromosomal genomic library with fetal muscle cDNA. Five of the clones have been localised to the short arm and four to the long arm. The short arm probes have been regionally assigned using a panel of somatic cell hybrids. They have been mapped further using a series of DNA samples from male patients with different deletions of the region Xp21, and having complex phenotypes including Duchenne muscular dystrophy. The use of these probes in the mapping of the short arm of the X chromosome is discussed.

Submicroscopic interstitial deletion of the X chromosome explains a complex genetic syndrome dominated by Norrie disease

Norrie disease (ND), an X-linked recessive disorder, is characterized by congenital blindness followed by bulbar atrophy. We have examined a three-generation family in which ND is part of a complex X-linked syndrome with severe mental retardation, hypogonadism, growth disturbances, and increased susceptibility to infections as additional features. This syndrome is apparently due to an interstitial deletion, as evidenced by the failure of the L1.28 DNA probe (DXS7 locus, Xp11.3) to detect complementary DNA sequences on the defective X chromosome of an affected male and of several obligatory heterozygotes. Attempts to further define this deletion with other DNA probes from the proximal short arm of the X chromosome or by prometaphase chromosome analysis were unsuccessful.

Toward early diagnosis of myotonic dystrophy: construction and characterization of a somatic cell hybrid with a single human der(19) chromosome

We have constructed a somatic cell hybrid line, designated 908K1, with a single human der(19) chromosome on a Chinese hamster background by employing conventional as well as microcell-mediated cell fusion techniques. The der(19) chromosome comprises the 19p13.1----q13.2 segment, as well as the distal (Xq24----qter) portion of the X chromosome long arm, and is stably retained by HAT selection. Extensive characterization of this hybrid line and comparison with other somatic cell hybrids has enabled us to regionally assign PGK2 to the distal short arm of chromosome 19 and to narrow down the assignments of CYP1, TGFB, and ERCC1 on 19q. Moreover, a cosmid library has been constructed from this microcell hybrid. By screening this library, as well as a chromosome 19-enriched library obtained elsewhere, 14 single-copy probes have been isolated that map on the 19p13.1----q13.2 segment, and 5 probes were assigned to the distal Xq. It is anticipated that these probes will be useful for the diagnosis of myotonic dystrophy and fra(X) mental retardation.

Close linkage between Norrie disease, a cloned DNA sequence from the proximal short arm, and the centromere of the X chromosome

Norrie disease (ND) is an X-linked recessive disorder with congenital blindness (atrophia bulborum hereditaria, pseudoglioma). Six kindreds segregating for ND were studied for linkage with polymorphic markers of the human X chromosome. No recombination was observed between the ND-locus (NDP) and the DXS7 locus, the latter followed as a DNA-restriction fragment length polymorphism, detected by the recombinant DNA probe L1.28, and assigned to the region Xp11.2-Xp11.3. The maximum lod scores are zeta = 3.81 at theta = 0.00. Linkage data between NDP and the other genetic markers used in the present study are in keeping with this assignment of the mutation to the proximal Xp.

X-linked retinitis pigmentosa: linkage with the centromere and a cloned DNA sequence from the proximal short arm of the X chromosome

A large Danish pedigree segregating for X-linked retinitis pigmentosa (RPX) (Warburg and Simonsen 1968) was restudied for linkage analysis. Using two markers, i.e. the DNA base sequence polymorphism presented by the probe L1.28 defining the chromosomal segment DXS7, and the C-banding heteromorphism (Xcen) (Friedrich 1982), we were able to localize the RPX gene in Xp close to the centromere rather precisely. The gene order could be deduced by three-point linkage analysis, and the gene distances were determined by pairwise analysis using the LIPED program (Ott 1974). Together with previously published data concerning the RPX:DXS7 linkage (Bhattacharya et al. 1984) a regional gene map is constructed. Xcen-11 cM-RPX-6 cM-DXS7.

X inactivation patterns in two syndromes with probable X-linked dominant, male lethal inheritance

For Incontinentia pigmenti Bloch-Sulzberger (IP) and Aicardi syndrome, an X-linked dominant transmission with lethality in hemizygous males has been proposed. The typical transition from inflammation to verrucous hypertrophy and hyperpigmented skin areas in IP suggests a gradual replacement of defective cells by normal cells. This would imply a preferential inactivation of the X chromosome carrying the IP gene with a proliferative advantage of this cell population. We have confirmed this hypothesis by demonstrating that the same X chromosome is preferentially active in fibroblasts grown from normal and hyperpigmented skin of an affected girl. In contrast, X inactivation was random in a girl with Aicardi syndrome.

X-linked dominant Charcot-Marie-Tooth disease: suggestion of linkage with a cloned DNA sequence from the proximal Xq

A large kindred with the X-linked dominant form of peroneal muscular atrophy (Charcot-Marie-Tooth disease) was analyzed for individual variation in the length of DNA fragments after restriction endonuclease digestion. A systematic search was performed for linkage with a series of cloned single-copy DNA sequences of known regional assignment to the human X chromosome. Close linkage was found with the pDP34 probe (DXYS1 locus, Xq13-q21), suggesting that the gene responsible for the disease is located on the proximal long arm of the X chromosome.