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Biomedical subjects

D J Shaw

Publications and source records attributed to D J Shaw.

At least 73 records · Page 4Linked to original sources
PubMed1992

Unstable DNA sequence in myotonic dystrophy.

A variable DNA sequence has been detected in patients with myotonic dystrophy. We set out to determine whether identification of this specific molecular defect would improve clinical management of patients and families with myotonic dystrophy. 127 affected patients who were studied had an expanded DNA fragment not seen in 73 normal controls. The increase in length of the fragment correlated broadly with disease severity, and we noted expansion of the sequence in successive generations of the same family. Progressive expansion of the affected gene provides a molecular explanation for an apparently earlier onset in successive generations (anticipation) in myotonic dystrophy and supports the role of an unstable repeat sequence as the basis of the defect. The specificity of this finding will assist in accurate diagnosis of myotonic dystrophy and genetic counselling of affected families.

Adolescent↗
PubMed1992

Expansion of an unstable DNA region and phenotypic variation in myotonic dystrophy.

Myotonic dystrophy is the commonest adult form of muscular dystrophy, with an estimated incidence of 1 per 7,500, although this is likely to be an underestimate because of the difficulty of detecting minimally affected individuals. It is a multisystem autosomal dominant disorder of unknown biochemical basis. No case of new mutation has been proven. We have isolated a human genomic clone that detects novel restriction fragments specific to individuals with myotonic dystrophy. A two-allele EcoRI polymorphism is seen in normal individuals, but in most affected individuals one of the normal alleles is replaced by a larger fragment, which varies in length both between unrelated affected individuals and within families. The unstable nature of this region may explain the characteristic variation in severity and age at onset of the disease. A second polymorphism at this locus is in almost complete linkage disequilibrium with myotonic dystrophy, strongly supporting our earlier results which indicated that most cases are descended from one original mutation.

Blotting, Southern↗
PubMed1992

Physical and genetic characterization of the distal segment of the myotonic dystrophy area on 19q.

The mutation involved in myotonic dystrophy (DM) has been mapped to the region between the ERCC1 DNA repair gene and the anonymous D19S51 locus on 19q13.3. Starting at locus D19S112 (probe pX75b), which served as a novel entry site for this chromosome region, we have established a cosmid contig of approximately 200 kb. In the contig, a gene expressed in the brain and a highly informative, 12-allele (TG)n variable simple sequence motif (VSSM) were identified. With this marker, designated X75b-VSSM, a highly characteristic size distribution of alleles linked with DM, which differed significantly from that on normal chromosomes, was observed. Combining our physical mapping and genetic data, we show that the X75b-VSSM marker is the closest distal to DM, thus excluding the DM mutation from the entire telomeric portion of the ERCC1-D19S51 region.

Base Sequence↗
PubMed1992

Molecular analysis for the myotonic dystrophy mutation in neuromuscular disorders.

A variable expansion of an unstable CTG repeat has been identified as the causal mutation for myotonic dystrophy. Standard molecular genetic techniques can now supplement traditional assessment protocols in a variety of clinical neurological situations where diagnostic uncertainty prevailed. Southern analysis using DNA probes which identify the expanded sequence, supplemented by direct PCR analysis for repeat number, provides a specific sensitive diagnostic test for myotonic dystrophy.

Adult↗
PubMed1992

Minimal expression of myotonic dystrophy: a clinical and molecular analysis.

A clinical and molecular study is reported of 83 patients considered to be minimally affected with myotonic dystrophy (DM). These had been identified in three ways: 60 subjects were identified on clinical grounds and were divided into those with and those without neuromuscular involvement (groups I and II); nine subjects were at high risk of carrying the DM gene but had a normal phenotype (group III); and 14 were parents of definitely affected patients where neither parent showed clinical abnormalities (group IV). PCR analysis of the CTG repeat in the DM gene showed a range of 70 to 230 repeats for the younger at risk patients in group III, while the asymptomatic gene carriers in group IV had 53 to 60 repeats. The sensitivity of diagnosis by EMG was found to be 39%. For ophthalmic signs this was 97.5%. This suggests that assignment on the basis of minimal clinical features carries a significant error. Molecular analysis, in conjunction with established clinical investigations, should prove valuable in the identification and exclusion of minimal myotonic dystrophy.

Adult↗
PubMed1992

Specific molecular prenatal diagnosis for the CTG mutation in myotonic dystrophy.

The results of DNA analysis for the specific mutation of myotonic dystrophy are reported in eight pregnancies (two studied retrospectively) in six families. Four results were normal; in the other four, large DNA expansions were found, comparable to the range seen in severely affected children with congenital onset of the disorder. The results agreed with those obtained by linked DNA markers in the six cases where they were available. We conclude that specific molecular prenatal diagnosis of myotonic dystrophy is feasible, and that an abnormal result may also give a guide to possible severity, though this should be interpreted with caution until greater experience is available.

Base Sequence↗
PubMed1992

User interactions with the PDQ cancer information system.

Searches by end users and intermediaries on the online PDQ (Physician Data Query) cancer information system were observed. With the National Library of Medicine (NLM) menu-based interface, end users (physicians) averaged fewer steps per question, while with the BRS command-drive interface, intermediaries appeared to be more efficient. Cancer Information Service (CIS) searchers, who have more PDQ experience than end users or intermediaries, made greater use of command stacking to anticipate menu selections. Retrieval was more complete in the NLM system, where both the menus and predefined print formats assisted the searchers.

Databases, Factual↗
PubMed1992

The inhibitory effects of cromakalim and its active enantiomer BRL 38227 against various agonists in guinea pig and human airways: comparison with pinacidil and verapamil.

The effects of the potassium channel activators, cromakalim, BRL 38227 and pinacidil, and the calcium antagonist, verapamil, have been compared against various spasmogens on airway responses in vitro and in vivo in the guinea pig and also in human isolated bronchi. In guinea pig tracheal spirals, potassium channel activators generally had a greater inhibitory effect than verapamil against tone induced by a wide range of spasmogens (spontaneous, 5-hydroxytryptamine, leukotriene D4, prostaglandin E2). The potassium channel activators had very little effect against potassium chloride- and carbachol-induced tone in guinea pig tracheal spirals [e.g., cromakalim (20 microM) induced relaxations of 0.21 +/- 0.03 (relative to an isoprenaline maximum = 1.0, mean +/- S.E.M.) against carbachol, compared to 0.77 +/- 0.03 against histamine]. In vivo, the potassium channel activators prevented histamine and 5-hydroxytryptamine-induced bronchoconstrictions, but had little inhibitory effect against acetylcholine. In contrast, in human bronchi, cromakalim was capable of inducing powerful concentration-dependent relaxations against carbachol-induced tone [cromakalim (20 microM) induced relaxations of 0.77 +/- 0.09 (relative to isoprenaline = 1.0, mean +/- S.E.M.) against carbachol, compared to 0.95 +/- 0.04 against histamine]. In human bronchi, all the inhibitory agents were more potent and more effective, except that verapamil did not have an increased maximum response. We conclude that potassium channel activators should be effective at relaxing contractions induced by a wide range of spasmogens in man.

Animals↗
PubMed1992

Anticipation in myotonic dystrophy: new light on an old problem.

The concept of anticipation, the occurrence of a genetic disorder at progressively earlier ages in successive generations, has been debated from the early years of this century, with myotonic dystrophy as the most striking example. Throughout most of this period there has been controversy as to whether the phenomenon resulted from observational and ascertainment biases or reflected a more fundamental mechanism. The recent discovery of inherited unstable DNA sequences, first in fragile-X mental retardation and now in myotonic dystrophy, not only confirms that anticipation indeed has a true biological basis but provides a specific molecular mechanism for it; this discovery can explain many of the puzzling anomalies in the inheritance of myotonic dystrophy and may prove relevant to comparable problems in other genetic disorders.

Chromosome Fragility↗
PubMed1991

Localisation of the myotonic dystrophy locus to 19q13.2-19q13.3 and its relationship to twelve polymorphic loci on 19q.

The order of fourteen polymorphic markers localised to the long arm of human chromosome 19 has been established by multipoint mapping in a set of 40 CEPH (Centre d'Etude de Polymorphisme Humain, Paris) reference families. We report here the linkage relationship of the myotonic dystrophy (DM) locus to twelve of these markers as studied in 45 families with DM. The resulting genetic map is supported by the localisation of the DNA markers in a panel of somatic cell hybrids. Ten of the twelve markers have been shown to be proximal to the DM gene and two, PRKCG and D19S22, distal but at distances of approximately 25 cM and 15 cM, respectively. The closest proximal markers are APOC2 (apolipoprotein C-II) and CKM (creatine kinase, muscle) approximately 3 cM and 2 cM from the DM gene respectively, in the order APOC2-CKM-DM. The distance between APOC2, CKM and DM (of the order of 2 million base pairs) and their known orientation should permit directional chromosome walking and jumping. The data presented here should enable us to determine whether or not new markers are distal to APOC2/CKM and thus potentially flank the DM gene.

Chromosome Banding↗
PubMed1991

Identification of new DNA markers close to the myotonic dystrophy locus.

The most useful markers for the prenatal diagnosis of myotonic dystrophy (DM) are APOC2 and CKM, both of which map proximal to DM. In order to produce other markers useful for DM, we have screened genomic DNA libraries constructed from cell line 20XP3542-1-4, which contains 20 to 30 Mb of human material including APOC2 and CKM. Of 51 human clones identified, seven map to chromosome 17, four to chromosome 8, and nine to chromosome 19, and the remaining 31 were excluded form chromosome 19 but not localised further. Four of the clones from chromosome 19 map distal to CKM and two of these clones (D19S62 and D19S63) are closely linked to DM. Analysis of a family in which a crossover between CKM and DM has occurred shows that neither D19S62 nor D19S63 and DM have recombined, suggesting that D19S62 and D19S63 are either closer to or flanking DM in relation to CKM. Pulsed field gel analysis showed that CKM, D19S62, and D19S63 map to a region of at least 1500 kb.

Blotting, Southern↗
PubMed1991

Paternal origin of the chromosomal deletion resulting in Wolf-Hirschhorn syndrome.

DNA samples were obtained from children with Wolf-Hirschhorn syndrome and their parents to assist with gene mapping studies of 4p16.3 (the region known to contain the Huntington's disease gene). A panel of seven families was studied, using polymorphic DNA markers, to determine the parental origin of the chromosome abnormality resulting in Wolf-Hirschhorn syndrome. All seven cases were the result of de novo deletions or rearrangements of 4p and in each case the abnormality arose on the paternal chromosome. Analysis of the 3' hypervariable regions of the alpha globin and mucin loci indicated that non-paternity was unlikely to be an explanation for these results. A paternal age effect was not observed. The possibilities of an environmental influence or genetic imprinting require further consideration. This report extends information regarding the preponderance of the paternal origin of de novo structural deletion syndromes.

Adult↗
PubMed1991

Detection of linkage disequilibrium between the myotonic dystrophy locus and a new polymorphic DNA marker.

We have examined the linkage of two new polymorphic DNA markers (D19S62 and D19S63) and a previously unreported polymorphism with an existing DNA marker (ERCC1) to the myotonic dystrophy (DM) locus. In addition, we have used pulsed-field gel electrophoresis to obtain a fine-structure map of this region. The detection of linkage disequilibrium between DM and one of these markers (D19S63) is the first demonstration of this phenomenon in a heterogeneous DM population. The results suggest that at least 58% of DM patients in the British population, as well as those in a French-Canadian subpopulation, are descended from the same ancestral DM mutation. We discuss the implications of this finding in terms of strategies for cloning the DM gene, for a possible role in modification of risk for prenatal and presymptomatic testing, and we speculate on the origin and number of existing mutations which may result in a DM phenotype.

Chromosomes, Human, Pair 19↗