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Biomedical subjects

D Williamson

Publications and source records attributed to D Williamson.

At least 55 records · Page 3Linked to original sources
PubMed1996

Haemoglobin Hallamshire (beta146 HIS --> TYR): a new high oxygen affinity haemoglobin responsible for familial erythrocytosis.

A new high oxygen affinity haemoglobin with the beta chain mutation beta146 HIS --> TYR is described. This variant was detected in a fit 34-year-old man with true erythrocytosis. The abnormal haemoglobin was identified as an extra band on cellulose acetate electrophoresis at pH 6.3 and was later confirmed by beta globin gene sequencing and oxygen dissociation studies. Whole blood containing Haemoglobin Hallamshire has a P50 of 18 mmHg. This newly described haemoglobin variant was also responsible for erythrocytosis in the mother and maternal half cousin of the index case. The identification of Haemoglobin Hallamshire provides confirmatory evidence of the important role of the C-terminal end of the chain in haemoglobin function.

Adult↗
PubMed1995

Haemoglobin Dhofar is linked to the codon 29 C-->T (IVS-1 nt-3) splice mutation which causes beta+ thalassaemia.

Investigations of a young man with apparent thalassaemia minor showed that he was a heterozygote for a rare abnormal haemoglobin variant, Hb Dhofar. The amino acid replacement is in the beta-globin chain (beta 58 Pro-->Arg) and is therefore not consistent with the observed proportion of Hb Dhofar, as in both this and the original case, it constituted only 15% of the total haemoglobin. We have determined the basis of the low expression of this mutant, which is due to its linkage to a thalassaemic splicing mutation on the same beta-globin gene at codon 29 (C-->T). The finding of this thalassaemia mutation linked to Hb Dhofar not only explains the low level of Hb Dhofar, but also provides evidence that the codon 29 C-->T, IVS-1 splice junction mutation causes a beta+ form of thalassaemia.

Base Sequence↗
PubMed1995

Parent and student preferences for services in a school-based clinic.

As a component of program planning for a school-based clinic in a suburban high school, a sample of 199 students and 196 parents were surveyed about preferences for health services. Parents and students were asked about health services desired and level of interest. Student overall interest in health services was less than parent interest, although both groups indicated at least a moderate level of interest. Both students and parents reported interest in availability of comprehensive services, including general health services, reproductive health services, and counseling services. The process of polling parents and students serves dual purposes of informing the population about school-based clinics, as well as gathering information to attempt to match the health services offered with needs identified.

Adolescent↗
PubMed1995

Childhood abuse as a factor in attrition from drug rehabilitation.

The following factors were examined as possible influences of clients' attrition from inpatient and outpatient drug-rehabilitation programs: depression (Center of Epidemiological Studies-Depression test), attributional style (Attributional Style Questionnaire), primary drug of choice, family incidence of substance abuse, and history of childhood physical abuse. A step-wise regression analysis indicated that a history of childhood abuse was a statistically reliable predictor of program noncompletion for 92 substance abusers who entered a drug-rehabilitation program.

Adult↗
PubMed1994

The chloride effect in human haemoglobin. A new kind of allosteric mechanism.

Chloride reduces the oxygen affinity of mammalian haemoglobin by acting as an allosteric effector that stabilizes the quaternary deoxy (T) structure. Perutz and others showed evidence that it does so by neutralizing electrostatic repulsion by an excess of positive charges in the cavity that runs through the centre of the molecule, but without binding to any specific site. On the basis of this proposal, any amino acid substitutions in the central cavity that halve the number of excess positive charges should halve the chloride effect, neutralization of the excess positive charges should inhibit it and introduction of additional positive charges should enhance it. Charge changes on the surface of the molecule should leave it unaltered. We have tested this proposal by measuring the chloride effects in several abnormal human haemoglobins with replacements of polar residues in the central cavity or on the surface that we happened to come across. They all proved consistent with the proposal. It appears that diffusible electrolytes can modify allosteric equilibria without necessarily binding to any specific site. Our proposal also implies that amino acid substitutions that make the central cavity more electropositive should destabilize the T-structure and therefore increase the oxygen affinity, while substitutions that make it more electronegative should do the reverse. A survey of all substitutions reported in the literature shows that this is true, with a few exceptions due to special stereochemical effects.

Allosteric Regulation↗
PubMed1994

The 24-hour pattern of prolactin secretion in depressed and normal adolescents.

Plasma prolactin concentrations were measured at 20-min intervals over a 24-hr period in 49 adolescents with major depressive disorder (MDD) and 39 normal control adolescents. Neither the pattern nor the amount of prolactin secretion was significantly different between these two groups. There were significant gender differences, with girls secreting more prolactin than boys, but no significant gender-by-diagnosis interactions were found. With the possible exception of psychosis, dividing the MDD sample based on clinical characteristics failed to reveal differences. These findings are discussed in the context of changes in prolactin in childhood depression using a serotonergic challenge study, as well as in relation to baseline prolactin studies in adult depression.

Adolescent↗
PubMed1994

Dental visiting behaviour and experiences of men with HIV.

To ascertain the dental visiting behaviour and experiences of men with HIV infection but without AIDS, a self-complete questionnaire was administered to convenience samples of men attending two genito-urinary medicine clinics. A total of 146 men completed questionnaires between December 1991 and June 1992. Of these, 85% had been regular or occasional attenders before diagnosis, 16% had not been to a dentist since diagnosis and 51% had changed their dentist. Although 63% had been to a general dental practitioner (GDP) at least once since diagnosis, half of them had withheld their HIV status at some time to obtain treatment. Of the 33% who had told their GDP of the diagnosis, half had been refused or offered limited treatment. The most common reasons for changing dentist, not visiting or withholding HIV status were concerns about the attitudes of the dental team and about confidentiality. Although regular oral examinations are of special importance to people with HIV their access to dental care is limited by their perceptions of dentists and the reported behaviour of dentists.

Adolescent↗
PubMed1994

Rett syndrome: controlled study of an oral opiate antagonist, naltrexone.

HYPOTHESIS: The opiate antagonist, naltrexone, will be beneficial in Rett syndrome. SUBJECTS: Twenty-five individuals fulfilling the criteria for Rett syndrome. METHOD: Randomized, double-blind, placebo-controlled crossover trial with two treatment periods, 4 months each, and an intervening 1-month washout period. Clinical stage, motor and cognitive development, motor-behavioral analysis, neurophysiological parameters (computerized electroencephalographic analysis, breathing characteristics, quantification of stereotyped hand movements, and sleep characteristics), and cerebrospinal fluid beta-endorphin measurements were evaluated at baseline and at the end of each treatment period. RESULTS: Only data from the first period of this study were analyzed due to significant sequence effects in the crossover design. This analysis indicated positive effects on certain respiratory characteristics including decreased disorganized breathing during wakefulness. Four (40%) of the individuals receiving naltrexone progressed one or more clinical stages versus none of the individuals receiving placebo. The adjusted (for baseline value and Rett stage) end of treatment psychomotor test age (Bayley Scales) was significantly higher for the placebo group. There was no significant change for the other parameters. CONCLUSION: Naltrexone may modify some of the respiratory disturbance in Rett syndrome. Declines in motor function and more rapid progression of the disorder suggest a deleterious effect.

Adolescent↗
PubMed1994

Maternal inheritance of extrachromosomal DNA in malaria parasites.

Plasmodium falciparum has two extrachromosomal genomes, the mitochondrial 6-kb DNA element and the 35-kb circular DNA. The mitochondrial gene cytochrome b on the 6-kb element has been shown to be inherited uniparentally. In order to ascertain whether the route is maternal or paternal we have examined preparations of male and female gametes of the closely related Plasmodium gallinaceum for the presence of extrachromosomal DNA. DNA from purified preparations of gametes was hybridised to probes for both the 6-kb and 35-kb extrachromosomal genomes. Both probes hybridised to the preparation of Plasmodium gallinaceum female gametes but not to that of the males. We conclude that the extrachromosomal DNAs of malaria parasites are transmitted maternally.

Animals↗
PubMed1994

Polycythaemia associated with homozygosity for the abnormal haemoglobin Sherwood Forest (beta 104 (G6)Arg-->Thr).

We describe a 22-year-old Pakistani male with polycythaemia associated with homozygosity for a high-affinity haemoglobin mutant, Hb Sherwood Forest. This haemoglobin variant has an amino acid substitution in the beta globin chain at position 104, Arg-->Thr. In the two previously reported instances of this haemoglobin mutant the individuals were heterozygotes and were haematologically normal. We show here that the homozygous state for the mutation is associated with a compensatory erythrocytosis resulting from decreased delivery of oxygen to the tissues. A family study showed that both parents and two siblings are heterozygotes for the haemoglobin mutant and are haematologically normal. To our knowledge, this represents the first example of a beta-globin mutation producing polycythaemia in homozygotes but not in heterozygotes.

Adult↗
PubMed1993

The unstable haemoglobins.

The unstable haemoglobin haemolytic anaemias result from the presence in the red cell of a structurally abnormal haemoglobin variant. There are many mutations producing unstable haemoglobins; most are single amino acid replacements that affect a few key areas of the haemoglobin structure. A wide range of haemoglobin instability is evident from in vitro studies, extending from mutants with a subclinical degree of instability to those associated with severe haemolytic disease. The characteristic feature of variants associated with haemolysis is a markedly decreased stability which is readily detectable by simple screening tests. The in vivo consequence is the precipitation of the unstable haemoglobin to give Heinz bodies which are associated with the red cell membrane and lead to premature cell destruction. The unstable haemoglobins have a greater tendency to spontaneously oxidise to methaemoglobin with subsequent formation of haemichromes and precipitation. This process is significantly accelerated by external factors such as exposure to oxidative substances and increased temperature; thus haemolytic crises are frequently associated with infections in otherwise asymptomatic carriers of unstable haemoglobins. The clinical expression of the unstable haemoglobin mutation may also be modified by proteolysis of the unstable globin chain in the bone marrow. This proteolytic mechanism can predominate in the case of extremely unstable globin chains to produce primarily a thalassaemic phenotype with little if any circulating unstable haemoglobin or evidence of haemolysis.

Amino Acid Sequence↗
PubMed1993

Depressed affect, hopelessness, and the risk of ischemic heart disease in a cohort of U.S. adults.

Major depression has been associated with mortality from ischemic heart disease (IHD). In addition, a symptom of depression--hopelessness--has been suggested as a determinant of health status. We studied the relation of both depressed affect and hopelessness to IHD incidence using data from a cohort of 2,832 U.S. adults age 45-77 years who participated in the National Health Examination Follow-up Study (mean follow-up = 12.4 years) and had no history of IHD or serious illness at baseline. We used the depression subscale of the General Well-Being Schedule to define depressed affect and a single item from the scale to define hopelessness. At baseline, 11.1% of the cohort had depressed affect; 10.8% reported moderate hopelessness, and 2.9% reported severe hopelessness. Depressed affect and hopelessness were more common among women, blacks, and persons who were less educated, unmarried, smokers, or physically inactive. There were 189 cases of fatal IHD during the follow-up period. After we adjusted for demographic and risk factors, depressed affect was related to fatal IHD [relative risk = 1.5; 95% confidence interval (CI) = 1.0-2.3]; the relative risks of fatal IHD for moderate and severe levels of hopelessness were 1.6 (95% CI = 1.0-2.5) and 2.1 (95% CI = 1.1-3.9), respectively. Depressed affect and hopelessness were also associated with an increased risk of nonfatal IHD. These data indicate that depressed affect and hopelessness may play a causal role in the occurrence of both fatal and nonfatal IHD.

Aged↗
PubMed1993

The K88 fimbrial adhesin of enterotoxigenic Escherichia coli binds to beta 1-linked galactosyl residues in glycosphingolipids.

The K88 fimbrial adhesin enables certain strains of enterotoxigenic Escherichia coli to adhere to the porcine small intestine. In this study, the ability of the K88 adhesin to bind to glycosphingolipids was monitored by modified enzyme-linked immunosorbent assay and thin-layer chromatography overlay binding analysis. The binding of the K88 adhesin to glycosphingolipid-coated microtiter plates was saturable, with 50% maximal binding occurring with gangliotriaosylceramide, gangliotetraosylceramide, and lactosylceramide at 67 +/- 21, 117 +/- 21, and 73 +/- 22 pM, respectively. Thin-layer chromatography overlay binding analysis demonstrated that serotype O8:K87:K88ab:H19 E. coli bound to hydroxylated galactosylceramide, gangliotriaocylceramide, gangliotetraosylceramide, and lactosylceramide but not to globotriaosylceramide, nonhydroxylated galactosylceramide, glucosides, glucosylceramide, or a mixture of ceramides. The K88 adhesin did not bind by either assay to globoside, the Forssman glycolipid, GM1, GM2, GM3, GD1a, GD2, GD3, GQ1b, or GT1b. The binding pattern observed with the K88 adhesin suggests that beta 1-linked galactosyl residues are the minimum determinant required for binding, provided they are presented correctly. It is suggested that beta 1-linked galactose residues may form the molecular basis of both glycoprotein and glycolipid receptors for the K88 fimbrial adhesin in the porcine small intestine.

Adhesins, Escherichia coli↗
PubMed1992

Structure-function relationships in the low-affinity mutant haemoglobin Aalborg (Gly74 (E18)beta----Arg).

Haemoglobin Aalborg (Gly74 (E18)beta----Arg) has a reduced oxygen affinity, in both the absence and the presence of organic phosphates; it has a raised affinity for organic phosphates, and it is moderately unstable. By contrast, haemoglobin Shepherds Bush (Gly74 (E18)beta----Asp) has an increased oxygen affinity in both the absence and the presence of organic phosphates, a diminished affinity for organic phosphates and is also unstable. We have determined the crystal structure of deoxyhaemoglobin Aalborg at 2.8 A resolution and compared it to the structures of deoxy- and oxyhaemoglobin A and of deoxyhaemoglobin Shepherds Bush. The guanidinium group of Arg74(E18)beta protrudes from the haem pocket and donates hydrogen bonds to the E and F helices. The carboxylate group of Asp74(E18)beta forms a hydrogen bond only with residue EF6 and is partially buried, which may be why haemoglobin Shepherds Bush appears to be more unstable than haemoglobin Aalborg. To discover why the latter has a low oxygen affinity, we superimposed the B, G and H helices of haemoglobin A, whose conformation is known to be unaffected by ligand binding, on those of haemoglobin Aalborg. This also brought helices E and the haems into superposition, but revealed a shift of the F helix of deoxyhaemoglobin Aalborg towards the EF-corner. This shift is opposite to that which occurs on ligand binding and on transition to the quaternary oxy-structure, and is linked to an increased tilt of the proximal histidine residue away from the haem axis. Since the relative positions of helices E and F and of the haem group are thought to be the main determinants of the changes in oxygen affinity, the shift of helix F may account for the reduced oxygen affinity of haemoglobin Aalborg. The shift may be due to a combination of steric and electrostatic effects introduced by the arginine residue's side-chain. The effects of the arginine and aspartate substitutions at position E18 beta on the 2,3-diphosphoglycerate affinity are equal and opposite. They can be quantitatively accounted for by the electrostatic attraction or repulsion by the oppositely charged side-chains.

Amino Acid Sequence↗