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Biomedical subjects

R Williamson

Publications and source records attributed to R Williamson.

At least 289 records · Page 16Linked to original sources
PubMed1988

Genetic differences between cystic fibrosis with and without meconium ileus.

41 families with cystic fibrosis, (CF) were tested for restriction fragment length polymorphisms (RFLPs) detected by four DNA probes all of which are tightly linked to the CF gene. 17 of the families had an affected child with, and 24 had one without, meconium ileus. In all cases, CF segregates with these gene probes; however, those with and those without meconium ileus differed in haplotype for CF chromosomes with respect to pJ3.11, which suggests that because of multiallelism (different mutations of the same locus) some CF patients present with meconium ileus and others do not.

Alleles↗
PubMed1988

Chromosomal localisation of a developmental gene in man: direct DNA analysis demonstrates that Greig cephalopolysyndactyly maps to 7p13.

Greig cephalopolysyndactyly syndrome (GCPS) is a rare autosomal dominant form of complex polydactyly. GCPS has been tentatively assigned to chromosome 7 on the basis of association of the condition with balanced translocations involving the short arm of chromosome 7 (7p13) in two families. Seven GCPS pedigrees with no chromosome abnormality were studied, and linkage was demonstrated between GCPS and the DNA sequence coding for the receptor for epidermal growth factor (localised to 7p12-13) (Z = 3.17; O = theta).

Chromosomes, Human, Pair 7↗
PubMed1988

Detection of a rare-cutter RFLP in a CpG-rich island near the cystic fibrosis locus.

The probe pCS.7, isolated from an HpaII tiny fragments (HTF) island and tightly linked to the mutation causing cystic fibrosis (CF), detects a polymorphism with the rare-cutter restriction enzyme BssHII. In a single digest, the resulting restriction fragment length polymorphism (RFLP) cannot be detected by either conventional or pulse-field gel electrophoresis. A double digest with BssHII in conjunction with a six-cutter restriction enzyme that does not recognize a site containing a CpG dinucleotide enables the probe to be used routinely for prenatal diagnosis and carrier exclusion. This strategy can be used to identify polymorphisms in HTF islands.

Alleles↗
PubMed1988

Mechanisms of beta-lactam resistance in Haemophilus influenzae.

Haemophilus influenzae has become increasingly resistant to beta-lactam antibiotics. Three major mechanisms, both enzymatic and non-enzymatic, are involved. Enzymatic resistance is mainly due to production of a TEM-1 plasmid-mediated beta-lactamase, and in some cases to a new enzyme ROB-1. Of the non-enzymatic mechanisms, decreased permeability due to alteration of outer membrane proteins seems to be rare in comparison to decreased affinity of penicillin-binding proteins for beta-lactam antibiotics. Enzymatic resistance is present in about 10-20% of clinical isolates, while non-enzymatic resistance is present only in 2-4%.

Anti-Bacterial Agents↗
PubMed1988

A long-range restriction map encompassing the cystic fibrosis locus and its closely linked genetic markers.

The cystic fibrosis (CF) locus has been localized to the long arm of chromosome 7 by linkage analysis, and the genetic relationship between CF and the probes J3.11, met, and 7C22 has been extensively studied. To extend this genetic analysis to higher resolution, to provide information on physical distances underlying the genetic relationships, and to set limits to the position of the cystic fibrosis mutation, we have constructed a partial restriction map covering approximately 5 Mb that defines the physical relationship between these and the more recently isolated markers CS.7, XV-2c, Lcn2, and C2/5. Allelic association indicates that CS.7 and XV-2c are close to the CF locus, and an expressed sequence from this region has been described as a candidate gene for this mutation (X. Estivill et al., 1987, Nature (London) 326: 840-845). Using pulsed-field gel electrophoresis we have determined the physical order of these markers to be cen-7C22-Lcn2-met-C2/5-XV-2c-CS.7-J3.11-tel and have localized the CF mutation to an interval of less than 1500 kb. A (not unexpected) disproportionality was observed between the currently best estimates of genetic and physical distances, with the interval J3.11-met showing an approximately fourfold higher frequency of recombination than the met-7C22 interval.

Chromosome Mapping↗
PubMed1988

Chorionic gonadotrophin-beta mRNA, a trophoblast marker, is expressed in human 8-cell embryos derived from tripronucleate zygotes.

Human chorionic gonadotrophin beta (HCG-beta) is a trophoblast marker. Its expression is normally limited to syncytiotrophoblast cells of chorionic villi, although it is known to be secreted from the human embryo as early as 7 days post-fertilization. To examine the onset of embryonic transcriptional activity of the gene encoding this polypeptide we have performed in-situ hybridization to cellular RNAs of human tripronucleate preimplantation embryos. We see expression of HCG-beta RNA at the 6-8-cell stage, before morphological differentiation between trophectoderm and inner cell mass is apparent. We believe that this RNA is the product of de novo transcription from the embryonic genome, since transcripts are only observed in embryos of at least 2 days post-fertilization in age.

Blastocyst↗
PubMed1988

Dissemination of the novel plasmid-mediated beta-lactamase CTX-1, which confers resistance to broad-spectrum cephalosporins, and its inhibition by beta-lactamase inhibitors.

The novel beta-lactamase CTX-1 (pI 6.3) encoded on a transferable 84-kilobase plasmid was found in six different bacterial species. It was responsible for a significant decrease in susceptibility towards most penicillins and cephalosporins, except imipenem, temocillin, and cephalosporins which have a 7-alpha-methoxy substituent. Synergy between either ampicillin, piperacillin, cefotaxime, ceftazidime, or aztreonam and three beta-lactamase inhibitors (clavulanic acid, sulbactam, and YTR 830) was generally found for different strains harboring CTX-1. This enzyme may be related to or derived from the TEM enzyme, since an intragenic probe of the TEM-1 gene hybridized with a fragment of the plasmid carrying CTX-1.

Cephalosporins↗
PubMed1988

Mutation of Salmonella paratyphi A conferring cross-resistance to several groups of antibiotics by decreased permeability and loss of invasiveness.

A spontaneous one-step mutant of Salmonella paratyphi A selected on ampicillin showed cross-resistance to all beta-lactam antibiotics except imipenem and to aminoglycosides, chloramphenicol, tetracycline, trimethoprim, and quinolones. It also grew as small colonies. Examination of the cell envelope of the mutant showed a quantitative decrease in three major outer membrane proteins of 40.6, 39.6 (presumably porins), and 24 kilodaltons and quantitative as well as qualitative modifications in the ladder pattern of lipopolysaccharide. Direct evidence for decreased permeability in the mutant included reduced uptake of [3H]glucose and norfloxacin, reduced accessibility of aztreonam and benzylpenicillin to penicillin-binding proteins in whole cells, and decreased diffusion of lactose and cephaloridine into proteoliposomes that were reconstituted with outer membrane proteins from the mutant. There was also loss of invasiveness of the mutant into HeLa cells. We assume that a pleiotropic mutation was responsible for multiple alterations in the outer membrane components of the resistant mutant of S. paratyphi A.

Aminoglycosides↗
PubMed1988

Molecular approaches to dysmorphology.

The biochemical and physiological defects underlying human dysmorphic syndromes can now be approached using techniques of molecular biology. The genetic component of the causation of the dysmorphology can be studied in isolation from the environmental component by using large, rare families which exhibit the same phenotype as more complex multifactorial disorders, but inherit the mutation in a monogenic fashion. Such an analysis starts with the determination of linkage to a gene probe, followed by the use of newer techniques of molecular biology to enable cloning and sequencing of the mutated gene. Analysis of the gene product by amino acid sequence homology to other known proteins, and tissue specific expression, may place the defect within the cascade of events associated with development and differentiation. Once cloned, the gene can also be manipulated in transgenic laboratory animals and the effect of its mutation studied directly. The use of techniques of molecular biology to study the genetic aspects of dysmorphic syndromes will allow insight to be gained both into normal fetal development and into the causes of congenital malformations.

Animals↗