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Biomedical subjects

R G Worton

Publications and source records attributed to R G Worton.

At least 73 records · Page 4Linked to original sources
PubMed1988

A grandpaternally derived de novo deletion within Xp21 initially presenting in carrier females diagnosed as Kugelberg-Welander syndrome.

We report on two sisters with a history of muscle weakness and an electromyogram (EMG) diagnosis of Kugelberg-Welander syndrome (KWS) or juvenile spinal muscular atrophy. A half-brother to these women was diagnosed to have Duchenne muscular dystrophy (DMD). Using molecular probes, we identified a deletion within Xp21 in this isolated case of DMD. Sequences detected by pXJ1.1 are deleted, while fragments detected by pERT87 are intact. Both of these probes are derived from the DMD locus. We have shown that the affected sisters share with their half-brother DNA markers that are linked to the DMD gene and inherited from their maternal grandfather. Dosage analysis of Southern blots show monosomy for pXJ1.1, which has allowed us to determine carrier status within this family and to show that the half-sisters are manifesting DMD carriers.

Chromosome Deletion↗
PubMed1988

Localization of the mdx mutation within the mouse dystrophin gene.

We have mapped human and mouse X chromosome-specific genomic and cDNA probes through an interspecies Mus musculus/spretus pedigree which contains the mdx mutation. The positions of these markers relative to one another and to the mdx mutation were delineated. Using probes corresponding to segments of the human Duchenne muscular dystrophy (DMD) gene transcript, the position of a cross-hybridizing mouse equivalent gene (mDMD) was located. In more than 200 animals mapped, three were identified which show recombination within this mDMD gene. Analysis of these three animals shows that the mDMD gene is oriented with its 5' end centromeric and its 3' end telomeric on the mouse X chromosome. Furthermore, their recombinational breakpoints are on either side of the mdx mutation, thus providing the first unequivocal demonstration that the mdx mutation is located within the mDMD gene and defining limits within that gene between which the mutation must lie. Within that segment the evidence indicates that there is no major deletion of an exon as detectable by Southern blot analysis in mdx animals. The mdx mouse becomes important as an animal model for the study of the expression of the DMD gene and its developmental consequences, for transgenic and other corrective manipulations.

Animals↗
PubMed1988

Partial gene duplication in Duchenne and Becker muscular dystrophies.

Duchenne and Becker muscular dystrophies (DMD and BMD) are progressive muscle wasting disorders with an X linked recessive mode of inheritance. We have surveyed 120 unrelated patients with DMD or BMD for gene duplications using a series of genomic probes from within the DMD/BMD gene locus. In three patients, two with DMD and one with BMD, a duplicated region within the DMD/BMD locus has been shown by Southern blot analysis and transmission densitometry. In two cases a new restriction fragment spanning the duplication junction has been visualised, indicating that the duplications are tandemly arranged. Mendelian inheritance of the duplication has been shown in two families by following the segregation of the duplication junction fragment. The three duplication cases have been analysed with a cDNA probe isolated from the DXS206 region of the DMD/BMD locus and the duplication of a specific set of exons has been found in two cases. This study shows that all three duplications are internal to the gene and confirms that such a duplication can result in a genetic disorder through the disruption of exon organisation.

Child↗
PubMed1987

Molecular analysis of a constitutional X-autosome translocation in a female with muscular dystrophy.

The gene responsible for Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) maps to the X chromosome short arm, band Xp21. In a few females with DMD or BMD, the Xp21 region is disrupted by an X-autosome translocation. Accumulating evidence suggests that the exchange has physically disrupted the DMD/BMD locus to cause the disease. One affected female with a t(X;21)(p21;p12) translocation was studied in detail. The exchange points from both translocation chromosomes were cloned, restriction-mapped, and sequenced. The translocation is reciprocal, but not conservative. A small amount of DNA is missing from the translocated chromosomes; 71 to 72 base pairs from the X chromosome and 16 to 23 base pairs from the 28S ribosomal gene on chromosome 21.

Base Sequence↗
PubMed1986

Somatic events unmask recessive cancer genes to initiate malignancy.

A heritable mutation predisposes an individual to certain childhood malignancies, such as retinoblastoma and Wilms' tumor. The chromosomal locations of the genes responsible for the predisposition are known by linkage with chromosomal deletions and enzyme markers. A study of these tumors in comparison to the normal constitutional cells of the patients, using enzyme and DNA markers near the predisposing genes, has shown that these genes are recessive to normal wild-type alleles at the cellular level. Expression of the recessive phenotype (malignancy) involves the same genetic events that were observed in Chinese hamster cell hybrids carrying recessive drug resistance genes. In both the experimental and clinical situations, the wild-type allele is most commonly eliminated by chromosome loss with duplication of the mutant chromosome. Simple chromosome loss and mitotic recombination have been documented in both systems. In the remaining 30% of cases, inactivation or microdeletion of the wild-type allele are assumed to be responsible for expression of the recessive phenotype. Osteosarcoma is a common second tumor in patients who have had retinoblastoma. Studies with markers in osteosarcoma show that these tumors also result from unmasking of the recessive phenotype by loss of the normal allele at the retinoblastoma locus, whether or not the patient had retinoblastoma. Subsequent chromosomal rearrangements and amplification of oncogenes that occur in these homozygous tumors provide progressive growth advantage. In other malignancies, in which studies have so far focused on oncogene amplification and chromosomal rearrangements, unmasking of recessive mutations may also be the critical initiating events.

Animals↗
PubMed1986

Paternal inheritance of translocation chromosomes in a t(X;21) patient with X linked muscular dystrophy.

A number of DNA probes from the short arm of the X chromosome have been used to study the inheritance of the translocation chromosomes in a girl with an X; autosome translocation and muscular dystrophy. The two translocation chromosomes were found to be derived from the father's single normal X chromosome, ruling out maternal inheritance of a pre-existent mutation and enhancing the concept that the de novo translocation is responsible for the dystrophic phenotype.

Chromosomes, Human, Pair 21↗
PubMed1986

Molecular deletion analysis in Duchenne muscular dystrophy.

Study of 165 unrelated patients with X linked muscular dystrophy (117 with Duchenne and 48 with Becker dystrophy) has shown nine Duchenne cases (8% of the total) where a molecular deletion was detected using probes pERT87 or XJ1.1. No cytogenetic abnormalities were detectable in this unselected series of patients and no clear clinical or other differences were found between deletion and non-deletion cases. No deletions were found in the 48 Becker patients. Analysis of the families allowed unequivocal identification carrier status in females hemizygous for the deleted allele. Since some of the deletions were detected with only one of the two probes, it is important that both pERT87 and XJ1.1 are used when studying patients for molecular deletions.

Alleles↗
PubMed1986

Linkage analysis of polymorphisms within the DNA fragment XJ cloned from the breakpoint of an X;21 translocation associated with X linked muscular dystrophy.

Cloning of a DNA segment including the translocation breakpoint in a female with an X;21 translocation and X linked muscular dystrophy has led to identification of three subclones which detect polymorphic markers. The alleles of these markers, XJ1 X 1, XJ1 X 2, and XJ2 X 2, are in strong linkage disequilibrium. Linkage analysis in 31 families with Duchenne or Becker muscular dystrophy has shown recombination within the XJ segment in one case, and recombination of DMD with both the XJ segment and the pERT87 segment in a second, but has revealed no recombination between the XJ and pERT87 segments. The XJ markers increase the proportion of DMD and BMD families that are informative for carrier detection and prenatal diagnosis, but in view of the risk of recombination they must be used with caution. The site(s) of the DMD mutation(s) relative to the XJ and pERT87 markers, and the detailed molecular structure of the DMD region, remain to be determined.

Alleles↗
PubMed1984

Duchenne muscular dystrophy involving translocation of the dmd gene next to ribosomal RNA genes.

Duchenne muscular dystrophy (DMD) is a severe X-linked disorder leading to early death of affected males. Females with the disease are rare, but seven are known to be affected because of a chromosomal rearrangement involving a site at or near the dmd gene on the X chromosome. One of the seven has a translocation between the X and chromosome 21. The translocation-derived chromosomes from this patient have been isolated, and the translocation is shown to have split the block of genes encoding ribosomal RNA on the short arm of chromosome 21. Thus ribosomal RNA gene probes may be used to identify a junction fragment from the translocation site, allowing access to cloned segments of the X at or near the dmd gene and presenting a new approach to the study of this disease.

Animals↗
PubMed1984

A Canadian collaborative study of mosaicism in amniotic fluid cell cultures.

Data on chromosomal mosaicism was collected retrospectively on 12 386 amniotic fluid samples cultured over a 10 year period in 14 Canadian centres. Level I mosaicism (a single abnormal cell--excluding single cell monosomy) was encountered in 863 cases (7.1 per cent). Level II mosaicism (multiple cells with the same abnormality in a single flask or colony) was encountered in 138 cases (1.1 per cent). Level III mosaicism (multiple cells distributed over multiple flasks or colonies) was encountered in 34 cases (0.3 per cent). Analysis of the details of these cases allowed five major conclusions to be drawn: (1) Single cell abnormalities should not be taken as an indication of true fetal mosaicism. Only rarely will this interpretation prove to be incorrect. (2) Mosaicism involving multiple cells confined to a single flask should not be regarded as an indication of true fetal mosaicism. Only occasionally will this interpretation prove to be incorrect. (3) Mosaicism involving multiple cells distributed over more than one flask should be regarded as a strong indication of true fetal mosaicism. Sixty per cent will be confirmed by karyotype analysis of the fetus or infant. (4) Mosaicism of the XX/XY type is usually due to maternal cell contamination. Occasionally it can be a female fetus with XY cells from an unknown source. (5) The in situ or colony method of chromosome analysis has no clear advantage over the flask method for either the detection of true fetal mosaicism or for the ability to distinguish true mosaics from false positives.

Amniocentesis↗
PubMed1984

Expression of an X-linked muscular dystrophy in a female due to translocation involving Xp21 and non-random inactivation of the normal X chromosome.

A young female was diagnosed as having X-linked muscular dystrophy of the Duchenne type. Chromosome studies, including trypsin-Giemsa banding, Quinacrine fluorescence, and nucleolus organizer region (NOR) silver staining revealed an X-autosome reciprocal translocation t(X;21) (p21;p12). Utilizing both [3H] thymidine autoradiography and the BrdU-Hoechst 33258-Giemsa technique, lymphocytes and fibroblasts were found to show a preferential inactivation of the normal X suggesting the presence of a single mutant gene on the translocated X. This patient is one of seven reported cases of an X-linked muscular dystrophy associated with an X-autosome translocation. In all seven cases the exchange point in the X chromosome is in band p21 at or near the site of the Duchenne gene.

Adult↗
PubMed1984

Moderate-level gene amplification in methotrexate-resistant Chinese hamster ovary cells is accompanied by chromosomal translocations at or near the site of the amplified DHFR gene.

In previous studies, we have described several classes of methotrexate-resistant Chinese hamster ovary cell lines. Although the RI class is resistant because of an altered target enzyme, dihydrofolate reductase, the RIII class derived from RI cells is somewhat more resistant because of a moderate amplification of the altered dhfr structural gene (Flintoff et al., Mol. Cell. Biol. 2:275-285, 1982). In one RIII line, a translocation between the short arm (p) of chromosome 2 and the long arm (q) of chromosome 5 was observed, and the amplified RIII gene complex was mapped to the p arm of the 2p-marker chromosome derived from the translocation (Worton et al., Mol. Cell. Biol. 1:330-335, 1981). We tested the hypothesis that chromosomal translocation is a general feature of RIII cells and that such translocation involves a site at or near the dhfr structural gene. Thus, we examined four independently derived RIII-type mutants and found that each had a moderate amplification of the dhfr gene sequences, and karyotype analysis revealed that each carried a translocation involving the 2p arm at or near band 2p25. That this chromosomal rearrangement involves a site near the dhfr locus was demonstrated by mapping the altered but unamplified structural gene coding for the RI phenotype to the short arm of an unaltered chromosome 2. This suggests that a highly specific rearrangement involving an exchange at or near the site of the unamplified gene is a necessary prerequisite for the amplification process. A model for gene amplification involving chromosomal rearrangements and sister chromatid exchange is described.

Animals↗
PubMed1981

Isolation and characterization of Chinese hamster cell mutants resistant to the cytotoxic effects of chromate.

Stable mutants resistant to the toxic anion chromate have been isolated from a variety of Chinese hamster cell lines. The mechanism of chromate toxicity is not known, but it must involve internalization via the sulfate transport pathway. All mutant lines had a defective sulfate transport system, showing a 10-fold reduction in the rate of uptake of radioactive sulfate into the cell. The chromate resistance phenotype in CHO cell mutants behave recessively in somatic cell hybrids; in other cell lines the Chr(r) phenotype was partially expressed (codominant) in cell hybrids. Complementation analysis in cell hybrids between 18 different mutant pairs failed to reveal any complementation, indicating that chromate selects mutants primarily, if not exclusively, at a single gene locus.

Animals↗