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Biomedical subjects

A Collins

Publications and source records attributed to A Collins.

At least 181 records · Page 10Linked to original sources
PubMed1991

Error filtration, interference, and the human linkage map.

Typing error is a major problem in constructing human linkage maps, leading to incorrect orders and inflating map lengths. An error filter is incorporated into multiple pairwise analysis that corrects for inflation of map lengths and improves recovery of the correct order. Multipoint mapping is more sensitive to error, but when its output is adjusted for both error and interference, map lengths are no longer inflated in proportion to the number of loci and are close to those obtained by multiple pairwise analysis.

Algorithms↗
PubMed1991

Identification of a peptide inhibitor of the cardiac sarcolemmal Na(+)-Ca2+ exchanger.

The deduced amino acid sequence of the cardiac sarcolemmal Na(+)-Ca2+ exchanger has a region which could represent a calmodulin binding site. As calmodulin binding regions of proteins often have an autoinhibitory role, a synthetic peptide with this sequence was tested for functional effects on Na(+)-Ca2+ exchange activity. The peptide inhibits the Na(+)-dependent Ca2+ uptake (KI approximately 1.5 microM) and the Nao(+)-dependent Ca2+ efflux of sarcolemmal vesicles in a noncompetitive manner with respect to both Na+ and Ca2+. The peptide is also a potent inhibitor (KI approximately 0.1 microM) of the Na(+)-Ca2+ exchange current of excised sarcolemmal patches. The binding site for the peptide on the exchanger is on the cytoplasmic surface of the membrane. The exchanger inhibitory peptide binds calmodulin with a moderately high affinity. From the characteristics of the inhibition of the exchange of sarcolemmal vesicles, we deduce that only inside-out sarcolemmal vesicles participate in the usual Na(+)-Ca2+ exchange assay. This contrasts with the common assumption that both inside-out and right-side-out vesicles exhibit exchange activity.

Amino Acid Sequence↗
PubMed1991

Comparative experience with smooth and polyurethane breast implants using the Kaplan-Meier method of survival analysis.

Smooth-walled silicone implants have been widely used in breast surgery. Capsular contracture, causing undesirable firmness and spherical deformity, has been a common problem. Recent studies suggest that polyurethane-covered breast implants are associated with a lower incidence of capsular contracture. The statistical methodology employed in some of these studies, however, may be subject to criticism. Between July of 1984 and June of 1990 (72 months), 427 polyurethane breast implants were used in 279 patients and 439 smooth prostheses were used in 250 patients for a variety of aesthetic and reconstructive procedures. The occurrence of capsular contracture was carefully monitored and then analyzed using the Kaplan-Meier method of survival analysis. This method is particularly well suited to analysis of these types of clinical data because it allows for the fact that contractures occur at varying intervals after surgery and that follow-up of patients is incomplete. The probability of capsular contracture with smooth-walled prostheses was found to be significantly greater than with polyurethane-covered implants in each group of patients studied (p less than 0.05). Other complications occurred at a similar rate regardless of prosthesis type. This study supports the belief that polyurethane breast implants have a lower contracture rate; furthermore, it introduces the Kaplan-Meier method for analyzing the outcome of alternative plastic surgical therapies.

Breast↗
PubMed1991

Genetic epidemiology of ovarian cancer: segregation analysis.

The genetic epidemiology of ovarian cancer has been investigated by complex segregation analysis of 462 pedigrees ascertained through a normal consultant. The observed pattern of ovarian cancer is compatible with an autosomal dominant gene. The gene frequency of the abnormal allele is 0.0015-0.0026 with a lifetime penetrance of 0.74-0.79. The gene frequency accounts for a significant proportion of ovarian cancer in young women. By age 70 the majority of affected women are phenocopies. The results from this analysis should enable the risks of ovarian cancer to be more accurately estimated than by empiric methods for relatives of affected women, and can maximize the usefulness of screening programmes and future linkage studies.

Adult↗
PubMed1991

Genetic epidemiology of complex phenotypes.

A theory is given for complex phenotypes represented by an ordered polychotomy separately for affected (as severity) and for normals (as diathesis), with consideration of history, ascertainment, sampling frames, and phenotype systems. Nonrandom selection of probands by severity is permitted. Both probit and logistic models are developed in a form compatible with segregation and/or linkage analysis. Probabilities are set out in detail in the Appendix. This approach avoids problems that have been encountered with quantitative traits and correlated phenotypes, although using this information.

Genetics, Population↗
PubMed1991

The prevalence, aetiology and clinical significance of pseudo-sinusoidal fetal heart rate patterns in labour.

OBJECTIVE: To investigate the prevalence of sinusoidal and pseudo-sinusoidal fetal heart rate (FHR) patterns in labour and the relation between the characteristics of the FHR pattern and fetal outcome. DESIGN: A prospective observational study over a 6-month period in which all women who had continuous FHR monitoring in labour had their intrapartum cardiotocographs (CTGs) scrutinized for the presence of sinusoidal or pseudo-sinusoidal FHR patterns. SETTING: John Radcliffe Hospital, Oxford. SUBJECTS: 1520 women who had fetal monitoring during labour for various reasons. MAIN OUTCOME MEASURES: Both internal (electrocardiographic) and external (ultrasound) recordings of the FHR were analysed. Abnormal FHR patterns were related to obstetric characteristics and fetal outcome in terms of Apgar scores, umbilical artery pH and admission to the special care unit. RESULTS: No true sinusoidal FHR patterns were observed, but pseudo-sinusoidal FHR patterns were found in 230 of the 1520 CTGs examined (15%). Of these, 219 were classified as minor (amplitude 5-15 beats/min) and 11 as intermediate (amplitude 16-24 beats/min). Major pseudo-sinusoidal FHR patterns (amplitude greater than 24 beats/min) were not observed. Minor pseudo-sinusoidal FHR patterns had a mean duration of 21 (SD 13) min and typically occurred once or twice early in labour. Using logistic regression analysis a significant, independent relation was demonstrated between the presence of minor pseudo-sinusoidal FHR patterns and the use of pethidine (RR 1.84, 95% CI 1.3 to 2.59, P less than 0.0001) and epidural analgesia (RR 1.85, 95% CI 1.24 to 2.76, P less than 0.001). Intermediate pseudo-sinusoidal FHR patterns were found in association with both in utero fetal sucking and transient episodes of fetal hypoxia such as that caused by periodic umbilical cord compression. CONCLUSION: Pseudo-sinusoidal FHR patterns in labour will usually be associated with a normal fetal outcome but a careful fetal assessment is mandatory.

Blood Gas Monitoring, Transcutaneous↗
PubMed1990

Counting algorithms for linkage.

The Lander-Green algorithm is algebraically different from the EM algorithm that maximizes likelihood. In our experience the numerical difference is very small. Since computations are no easier or convergence faster for the Lander-Green algorithm, there is no reason to prefer it to EM. As suggested by Green (personal communication), layering is advantageous. Occasional updating of the information weights might also be considered to accelerate mapping.

Algorithms↗
PubMed1990

Standard maps of chromosome 10.

To achieve consensus more exact definitions of genetical maps are required, of which standard, comprehensive and skeletal might be some. A standard genetic map gives distance from pter in centimorgans (cM), uses the international nomenclature for assigned loci, is sex-specific, and allows as well as possible for interference and typing errors. A standard physical map gives distance from pter in megabases (Mb). A standard map is called comprehensive if it aims to include all syntenic loci, and skeletal if it is limited to loci whose order is well supported. Loci with established order are called skeletal, and are used to define regional assignments of other loci. These principles are illustrated using the CEPH data for chromosome 10. Map lengths by multiple 2-point analysis under supported interference are in good agreement with other evidence, but multipoint mapping gives a substantial overestimate. There are currently 21 loci in the skeletal genetic map and 40 loci in the comprehensive genetic map. From these data, cytogenetic assignments, and partial genetic maps the physical location has been estimated for 85 loci. MEN2A is in a region close to the centromere in which male recombination per megabase is much reduced. Order of DNA markers in this densely mapped region has not been determined, and therefore the exact location of MEN2A is uncertain, although it is likely to lie between D10S34 and D10S30 and close to D10S11.

Chi-Square Distribution↗
PubMed1990

The use of metabolic inhibitors in the analysis of eukaryotic DNA repair.

By now, it is well established that DNA repair can be inhibited. It is not surprising that many inhibitors of replicative DNA synthesis also effect repair, since the two processes involve similar biochemical steps carried out by analogous if not identical enzymes. No specific inhibitors of repair are known, and care must be taken when interpreting results to be sure that observed effects of inhibitors unambiguously relate to repair. With this caveat, it remains true that inhibitors are valuable tools for the dissection of repair pathways in the classic biochemical fashion, looking for accumulation of intermediates at a point before the enzymic step that is blocked.

Animals↗
PubMed1990

Failure of a knee prosthesis accelerated by shedding of beads from the porous metal surface.

A 61-year-old man who received a porous-metal-coated knee implant returned eight months later with chronic synovitis, instability, and loosening of his artificial joint. Subsequently, metal beads were detected in the joint space and soft tissues and were also embedded in the articulating surface of the tibial component. There was scoring of the tibial surface, and polyethylene wear particles were noted in the synovial and fibroconnective-tissue membranes, which had formed beneath the tibial component. Many particles were seen inside giant cells and macrophages. Failure in this case was probably accelerated by the granulomatous response in the soft tissue to wear particles. There was osteolysis rather than new bone growth at the interface with the tibial component. Analysis indicated that poor bead-bonding strength may have initiated the problem. Careful appraisal of the outcome from use of beaded porous-metal-coated devices and assurance of their adequate bonding strength are essential for further progress.

Foreign Bodies↗
PubMed1989

Glucose tolerance in Papua New Guinea: ethnic differences, association with environmental and behavioural factors and the possible emergence of glucose intolerance in a highland community.

That Melanesians of non-Austronesian genetic ancestry may be relatively resistant to glucose intolerance was supported by the results of a study of two semitraditional non-Austronesian villages in the Papua New Guinean highlands in 1983, in which an absence of diabetes and a high degree of glucose tolerance and insulin sensitivity were observed. The second of this series of surveys was conducted in 1985 in three non-traditional communities: a periurban, non-Austronesian village in the highlands, and rural and periurban Austronesian villages in coastal locations. Although an absence of diabetes was demonstrated once again in the highlanders, these periurban subjects showed an unexpectedly high insulin response which may be a precursor of glucose intolerance. The notion that highland communities that are living in non-traditional circumstances in Papua New Guinea presently are in "metabolic transition" towards diabetes and other non-communicable diseases, if correct, is of importance to the public health of the nation. In the periurban, coastal-dwelling Austronesians, diabetes with severe hyperglycaemia was demonstrated, and there was some evidence of a secular trend towards increasing glucose intolerance. The two-hour plasma glucose concentrations were shown to be associated with obesity, modernity and Seventh-Day Adventist religious persuasion. However, important and unexplained differences in glucose tolerance remained between rural and periurban coastal dwellers after taking these factors into account.

Adult↗