A cloned DNA segment from the telomeric region of human chromosome 4p is not detectably rearranged in Huntington disease patients

A radiation hybrid map of the distal short arm of human chromosome 11, containing the Beckwith-Wiedemann and associated embryonal tumor disease loci

We describe a high-resolution radiation hybrid (RH) map of the distal short arm of human chromosome 11 containing the Beckwith-Wiedemann gene and the associated embryonal tumor disease loci. Thirteen human 11p15 genes and 17 new anonymous probes were mapped by a statistical analysis of the cosegregation of markers in 102 rodent-human radiation hybrids retaining fragments of human chromosome 11. The 17 anonymous probes were generated from lambda phage containing human 11p15.5 inserts, by using ALU-PCR. A comprehensive map of all 30 loci and a framework map of nine clusters of loci ordered at odds of 1,000:1 were constructed by a multipoint maximum-likelihood approach by using the computer program RHMAP. This RH map localizes one new gene to chromosome 11p15 (WEE1), provides more precise order information for several 11p15 genes (CTSD, H19, HPX, ST5, RNH, and SMPD1), confirms previous map orders for other 11p15 genes (CALCA, PTH, HBBC, TH, HRAS, and DRD4), and maps 17 new anonymous probes within the 11p15.5 region. This RH map should prove useful in better defining the positions of the Beckwith-Wiedemann and associated embryonal tumor disease-gene loci.

Terminal deletion of chromosome 4p (4p16.3) shows a breakpoint between loci linked to Huntington disease

A 15-year-old boy with a terminal deletion of the short arm of chromosome 4 is described. The patient has a mild clinical phenotype that is incompatible with Wolf-Hirschhorn syndrome. Careful neurological examination including CT scan did not show any signs of Huntington disease. The chromosomal breakpoint was analyzed by means of polymorphic DNA probes localized close to the tentative Huntington (HD) locus. The breakage has occurred between D4S43 and D4S90 loci and thus deletes part of the chromosomal candidate regions for the HD locus.

Recombination of 4p16 DNA markers in an unusual family with Huntington disease

The Huntington disease (HD) mutation has been localized to human chromosome 4p16, in a 6-Mb region between the D4S10 locus and the 4p telomere. In a report by Robbins et al., a family was identified in which an affected individual failed to inherit three alleles within the 6-Mb region originating from the parental HD chromosome. To explain these results, it was suggested that the HD locus (HD) lies close to the telomere and that a recombination event took place between HD and the most telomeric marker examined, D4S90. As a test of this telomere hypothesis, we examined six members of this family, five of whom are affected with HD, for the segregation of 12 polymorphic markers from 4p16, including D4S169, which lies within 80 kb of the 4p telomere. We separated, in somatic cell hybrids, the chromosomes 4 from each family member, to determine the phase of marker alleles on each chromosome. We excluded nonpaternity by performing DNA fingerprint analyses on all six family members, and we found no evidence for chromosomal rearrangements when we used high-resolution karyotype analysis. We found that two affected siblings, including one of the patients originally described by Robbins et al., inherited alleles from the non-HD chromosome 4 of their affected parents, throughout the 6-Mb region. We found that a third affected sibling, also studied by Robbins et al., inherited alleles from the HD chromosome 4 of the affected parent, throughout the 6-Mb region. Finally, we found that a fourth sibling, who is likely affected with HD, has both a recombination event within the 6-Mb region and an additional recombination event in a more centromeric region of the short arm of chromosome 4. Our results argue against a telomeric location for HD and suggest that the HD mutation in this family is either associated with DNA predisposed to double recombination and/or gene conversion within the 6-Mb region or is in a gene that is outside this region and that is different from that mutated in most other families with HD.

Isolation and characterization of radiation-reduced hybrids containing portions of the proximal long arm of the human X chromosome: identification of hybrids containing the Menkes' disease locus

The proximal long arm of the human X chromosome (Xcen----Xq13) encompasses an estimated 23 megabases of DNA and contains numerous identified genetic loci. In order to generate a highly enriched source of DNA from this region, radiation-reduced human-hamster hybrids were constructed and screened to identify those that contained at least part of proximal Xq. Eight such hybrids were identified and characterized by Southern blot and fluorescence in situ hybridization analyses to determine more precisely the human DNA complement in each. One hybrid contains the entire proximal long arm and will be useful for mapping Xcen----Xq13 in its entirety and for localizing genes within this region. Another hybrid contains a smaller portion of the proximal long arm that includes the region reported to contain the gene for Menkes' disease.

Genetic linkage analysis of bipolar affective disorder in an Old Order Amish pedigree

We have used genetic linkage analysis in an effort to identify a gene responsible for bipolar affective disorder (BAD) in an Old Order Amish pedigree. The initial study of this pedigree showed strong evidence for linkage of the chromosome 11p15 markers HRAS1 and the insulin gene (INS) to BAD, whereas a second report found no evidence for linkage. We have independently determined the INS and HRAS1 genotypes from 81 individuals in this pedigree. A polymerase chain reaction (PCR) assay was used to score INS alleles that are difficult to distinguish from one another by conventional agarose gel electrophoresis. In addition, we used four separate diagnostic models to score individuals with psychiatric illness as either affected or unaffected. No evidence of significant linkage between BAD and the markers was found with either two-point or multipoint analysis regardless of which diagnostic model was used. However, exclusion of the region of chromosome 11 between INS and RAS1 as a possible location for the BAD gene in this family depended on the diagnostic model. Further genetic linkage studies with additional DNA markers that span the genome are necessary to determine the chromosomal location of the BAD gene in this family.

Isolation and characterization of new highly polymorphic DNA markers from the Huntington disease region

The defect causing Huntington disease (HD) has been mapped to 4p16.3, distal to the DNA marker D4S10. Subsequently, additional polymorphic markers closer to the HD gene have been isolated, which has led to the establishment of predictive testing programs for individuals at risk for HD. Approximately 17% of persons presenting to the Canadian collaborative study for predictive testing for HD have not received any modification of risk, in part because of limited informativeness of currently available DNA markers. Therefore, more highly polymorphic DNA markers are needed, which will further increase the accuracy and availability of predictive testing, specifically for families with complex or incomplete pedigree structures. In addition, new markers are urgently needed in order to refine the breakpoints in the few known recombinant HD chromosomes, which could allow a more accurate localization of the HD gene within 4p16.3 and, therefore, accelerate the cloning of the disease gene. In this study we present the identification and characterization of nine new polymorphic DNA markers, including three markers which detect highly informative multiallelic VNTR-like polymorphisms with PIC values of up to .84. These markers have been isolated from a cloned region of DNA which has been previously mapped approximately 1,000 kb from the 4p telomere.

Dinucleotide repeat polymorphism located at D4S169

Images

A new sequence variant of the human DNA ligase type I gene (LIG I)

Images

Linkage disequilibrium and recombination make a telomeric site for the Huntington's disease gene unlikely

In a Scottish family in which Huntington's disease (HD) was segregating, recombination was observed between the D4S115/S111 and D4S43/S95 loci, with the HD gene associated with the more proximal D4S43/S95 locus. Analysis of linkage disequilibrium in Scottish families showed significant non-random association between the HD gene and alleles at the D4S95 and D4S98 loci. This adds to previous evidence that the HD locus is not sited at the telomere of chromosome 4.

Defined physical limits of the Huntington disease gene candidate region

The Huntington disease (HD) gene has been mapped 4 cM distal to D4S10 within the telomeric chromosome band, 4p16.3. The published physical map of this region extends from D4S10 to the telomere but contains two gaps of unknown size. Recombination events have been used to position the HD mutation with respect to genetic markers within this region, and one such event places the gene proximal to D4S168, excluding the distal gap as a possible location for the defect. One previously published recombination event appeared to have excluded the proximal gap. We have reassessed this event and have moved the proximal boundary for the HD candidate region centromeric to the gap within a "hot spot" for recombination between D4S10 and D4S125. We have closed the proximal gap and report here the complete physical map spanning the HD candidate region from D4S10 to D4S168, the maximum size of which can now be placed accurately at 2.5 Mb.

Telomeres

Telomeres are essential for chromosome stability and replication. Maintaining a balance between telomere shortening and lengthening is essential for cell viability. Recent work on telomeres from yeast, Drosophila and mammals, and on telomerase has provided insight into the mechanisms of both the shortening and lengthening processes.