Search PubMed⌕ Search

Biomedical subjects

A D Webster

Publications and source records attributed to A D Webster.

At least 37 records · Page 2Linked to original sources
PubMed1999

Genetic linkage of IgA deficiency to the major histocompatibility complex: evidence for allele segregation distortion, parent-of-origin penetrance differences, and the role of anti-IgA antibodies in disease predisposition.

Immunoglobulin A (IgA) deficiency (IgAD) is characterized by a defect of terminal lymphocyte differentiation, leading to a lack of IgA in serum and mucosal secretions. Familial clustering, variable population prevalence in different ethnic groups, and a predominant inheritance pattern suggest a strong genetic predisposition to IgAD. The genetic susceptibility to IgAD is shared with a less prevalent, but more profound, defect called "common variable immunodeficiency" (CVID). Here we show an increased allele sharing at 6p21 in affected members of 83 multiplex IgAD/CVID pedigrees and demonstrate, using transmission/diseqilibrium tests, family-based associations indicating the presence of a predisposing locus, designated "IGAD1," in the proximal part of the major histocompatibility complex (MHC). The recurrence risk of IgAD was found to depend on the sex of parents transmitting the defect: affected mothers were more likely to produce offspring with IgAD than were affected fathers. Carrier mothers but not carrier fathers transmitted IGAD1 alleles more frequently to the affected offspring than would be expected under random segregation. The differential parent-of-origin penetrance is proposed to reflect a maternal effect mediated by the production of anti-IgA antibodies tentatively linked to IGAD1. This is supported by higher frequency of anti-IgA-positive females transmitting the disorder to children, in comparison with female IgAD nontransmitters, and by linkage data in the former group. Such pathogenic mechanisms may be shared by other MHC-linked complex traits associated with the production of specific autoantibodies, parental effects, and a particular MHC haplotype.

Alleles↗
PubMed1998

Ataxia-telangiectasia and T-cell leukemias: no evidence for somatic ATM mutation in sporadic T-ALL or for hypermethylation of the ATM-NPAT/E14 bidirectional promoter in T-PLL.

The ATM gene deficient in ataxia-telangiectasia, a recessive multisystem disease associated with a high risk of lymphomas and leukemias, was found previously to be inactivated in a rare sporadic malignancy, T-cell prolymphocytic leukemia (T-PLL), which is often associated with cytogenetic aberrations of chromosome 14. The ATM gene was shown to sustain frequent loss-of-function mutations in T-PLL tumor cells, consistent with functioning as a tumor suppressor gene in this leukemia. To investigate the possibility of nonmutational or nonrecombinational mechanisms of T-PLL development, we have used bisulfite genomic sequencing to analyze DNA methylation in the putative bidirectional promoter region of the closely linked ATM and NPAT/E14 genes within the CpG island at 11q22-q23. We show that this region is completely demethylated in lymphocytes expressing ATM; however, no extensive hypermethylation was found in 9 T-PLL tumor DNA samples without evidence of ATM/p53 mutations. Because acute T-cell lymphoblastic leukemias (T-ALL) were also observed in ataxia-telangiectasia patients and T-ALL tumor cells contain chromosome 14 abnormalities, 19 presentation samples of T-ALL patients were analyzed for ATM mutations. Although T-ALL patients exhibited rare nucleotide substitutions not previously found in ATM, all were identified in the germ-line, indicating constitutional polymorphisms, potentially confined to ethnic subpopulations. The absence of somatic nucleotide changes in ATM in T-ALL as compared with T-PLL suggests a distinct pattern of genetic events in the development of the two leukemias.

Ataxia Telangiectasia↗
PubMed1998

Discoid lupus erythematosus associated with a primary immunodeficiency syndrome showing features of non-X-linked hyper-IgM syndrome.

Hyper-IgM (HIM) syndrome is a rare primary immunodeficiency disorder. Approximately 120 cases have been described in the literature world-wide. Features of HIM include low serum IgG, a very low IgA with normal or high IgM levels. Autoimmune phenomena are recognized associations but connective tissue disorders have so far not been described in HIM patients. We report the case of a 19-year-old Indian woman with an immunodeficiency syndrome characteristic of non-X-linked HIM who developed discoid lupus erythematosus. Anti-double-stranded DNA antibodies were negative. Antibodies to extractable nuclear antigens were positive for Ro and nRNP, with evidence that they were of both IgG and IgM class. Treatment with hydroxychloroquine and topical steroids was successful.

Adult↗
PubMed1998

Primary defect in CD8+ lymphocytes in the antibody deficiency disease (common variable immunodeficiency): abnormalities in intracellular production of interferon-gamma (IFN-gamma) in CD28+ ('cytotoxic') and CD28- ('suppressor') CD8+ subsets.

We have measured by flow cytometry the ability of subsets of CD8+CD3+ lymphocytes within mononuclear cell preparations to make intracellular cytokines (IL-2, tumour necrosis factor-alpha (TNF-alpha) and IFN-gamma) on stimulation in vitro with phorbol myristate acetate (PMA) and ionomycin for 16 h. These CD8+ subsets were defined by the presence or absence of CD28 or HLA-DR. Subsets of normal CD8+ cells were compared with cells from the antibody deficiency disease common variable immunodeficiency (CVID). In CVID there was a significant increase in the production of IFN-gamma in the CD8+CD28+ subset ('cytotoxic'). This reflects a shift in this disease towards an excessive Th1 response away from B cell help. Paradoxically, some CVID patients also showed a reduction in IFN-gamma production in the CD8+CD28- subset ('suppressor') which was associated with a failure of these cells to maintain a state of activation after a stimulus in vitro. The B cell problem in this disease is known to be related to a failure of T cell help shown by an inability to produce the antigen-specific CD4+ memory T cells needed for successful B cell maturation. The two pathological CD28 subsets of CD8+ cells we have found in CVID may both be detrimental to a normal CD4-dependent immune response. The CD28- suppressor subset expands and is unable to maintain activation and cytokine secretion, and the CD28+ cytotoxic subset is over-producing the Th1 cytokine IFN-gamma.

Adult↗
PubMed1998

GB virus C infection in patients with primary antibody deficiency.

Sera from 77 patients with common variable immunodeficiency (CVID) were tested for GB virus C (GBV-C) RNA, because they are prone to unexplained chronic hepatitis, and from 28 patients with X-linked agammaglobulinemia (XLA) who have a similar primary antibody deficiency but are not prone to hepatitis. Eight CVID and 8 XLA patients were positive; 6 positive CVID and 3 XLA patients had abnormal liver enzymes, explained in 3 by either hepatitis B or C virus infection. Most patients tested had antibodies to the E2 antigen of GBV-C, apparently passively acquired from their immunoglobulin therapy. The high prevalence of GBV-C viremia in CVID and XLA patients is probably explained by their long-term exposure to blood products. Our data indicate that GBV-C does not cause chronic hepatitis in immunocompromised XLA patients and is not the cause of chronic non-B or -C hepatitis in the majority of CVID patients.

Adult↗
PubMed1998

Infection in patients with congenital immune deficiencies.

We review recent developments in the pathogenesis of the major immunodeficiencies, the pathogens involved, and new diagnostic and treatment options. Early diagnosis and prophylaxis are the mainstays in the current management of these immunological disorders. New advances, including the use of cytokines and growth factors, molecular diagnosis and a better understanding of the immunopathogenesis of infections, are discussed.

Journal Article↗
PubMed1998

Excavation of a Vietnam-era aircraft crash site: use of cross-cultural understanding and dual forensic recovery methods.

The excavation of a 23 year-old aircraft crash site in the Socialist Republic of Vietnam and the transformational processes preceding its excavation in 1995-1996 are detailed. The history of the site involved an initial catastrophic event, with subsequent reclamation and disturbances. Ultimately, a recovery effort by a joint U.S. team from the Central Identification Laboratory, Hawaii (CILHI). Joint Task Force-Full Accounting (JTF-FA) and a Socialist Republic of Vietnam contingent yielded numerous human remains, personal effects, and life-support items from the crash site. This case study should be of interest to the increasing number of forensic anthropologists who carry out work in international contexts. The application of forensic anthropology in human rights abuse cases, for example in Rwanda, Argentina, and Bosnia, provide examples of such cross-cultural endeavors. Cultural factors act in the development of a site and should not be overlooked as significant taphonomic agents. The approach that an indigenous person takes to a crash site or mass grave may be quite different from our own approach, involving Western science. Holland, Anderson, and Mann (I) describe the postmortem alternation of exhumed and/or curated bone caused by indigenous South-east Asian peoples; the examples provided by these authors demonstrate how culture affects the treatment of what we would call "evidence." The international nature of an incident can add complicating "filters" to the reconstruction of events, since reclamation responses by indigenous people vary according to their interpretations of the scene. An investigating forensic anthropologist needs to understand the emic viewpoint (the insider's view), as cultural anthropologists do, when attempting to recover and reconstruct such an incident. In response to the cultural (and natural) taphonomic agents at work on such a site, the use of dual forensic recovery methods--simultaneously treating the investigation scene like an aircraft crash and a clandestine burial site--is advised. Employing a flexible set of methods will allow for maximal recovery of evidence.

Accidents, Aviation↗
PubMed1997

Determination of intracellular cytokines by flow-cytometry following whole-blood culture.

Various methods have been reported for measuring intracellular cytokines in peripheral blood mononuclear cells isolated by density-gradient centrifugation. In this report, we describe a whole-blood method for the determination of intracellular cytokines (IFN-gamma, TNF-alpha and IL-2) that uses small-volume (500 microl) blood samples. Directly conjugated anti-cytokine antibodies and commercial cell membrane fixation and permeabilisation reagents were used. Blood was cultured in a 1:3 dilution with a combination of PMA and ionomycin to reveal the cytokine synthetic potential of each cell, together with monensin to increase the sensitivity by retaining cytokines within the cell to detectable levels. The optimum concentrations of PMA (10 ng/ml (16.2 nmol/l)), ionomycin (2 micromol/l) and monensin (3 micromol/l) were determined. Kinetic studies showed maximal cytokine expression after 2 h of culture for TNF-alpha and IFN-gamma and 4 h for IL-2. Assessment of TNF-alpha and IFN-gamma production within the CD4 and CD8 lymphocytes from 10 normal volunteers showed that considerably more CD8 + than CD4 + cells produced IFN-gamma. This technique could be used by routine immunology laboratories and will be of use in studies to determine whether cytokine assays are of value in the investigation of immune disorders.

Adult↗
PubMed1997

Mutation pattern in the Bruton's tyrosine kinase gene in 26 unrelated patients with X-linked agammaglobulinemia.

Mutation pattern was characterized in the Bruton's tyrosine kinase gene (BTK) in 26 patients with X-linked agammaglobulinemia, the first described immunoglobulin deficiency, and was related to BTK expression. A total of 24 different mutations were identified. Most BTK mutations were found to result in premature termination of the translation product. Mutations were detected in most BTK exons with a predominance of frameshift and nonsense mutations in the 5' end of the gene and missense mutations in its 3' part, corresponding to the catalytic domain of the enzyme. Nonsense and frameshift mutations were associated with diminished levels of BTK mRNA expression, except for a frameshift mutation in exon 17 and two nonsense mutations in exon 2, indicating that these cases are not confined to penultimate exons. One amino acid substitution (R28H) was found in the pleckstrin homology domain's residue, which is mutated in mice bearing the X-linked immunodeficiency phenotype; another substitution (R307G) was identified in the src homology domain 2. All remaining amino acid substitutions were found in the catalytic domain of Btk.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1997

Clustering of missense mutations in the ataxia-telangiectasia gene in a sporadic T-cell leukaemia.

Ataxia-telangiectasia (A-T) is a recessive multi-system disorder caused by mutations in the ATM gene at 11q22-q23 (ref. 3). The risk of cancer, especially lymphoid neoplasias, is substantially elevated in A-T patients and has long been associated with chromosomal instability. By analysing tumour DNA from patients with sporadic T-cell prolymphocytic leukaemia (T-PLL), a rare clonal malignancy with similarities to a mature T-cell leukaemia seen in A-T, we demonstrate a high frequency of ATM mutations in T-PLL. In marked contrast to the ATM mutation pattern in A-T, the most frequent nucleotide changes in this leukaemia were missense mutations. These clustered in the region corresponding to the kinase domain, which is highly conserved in ATM-related proteins in mouse, yeast and Drosophila. The resulting amino-acid substitutions are predicted to interfere with ATP binding or substrate recognition. Two of seventeen mutated T-PLL samples had a previously reported A-T allele. In contrast, no mutations were detected in the p53 gene, suggesting that this tumour suppressor is not frequently altered in this leukaemia. Occasional missense mutations in ATM were also found in tumour DNA from patients with B-cell non-Hodgkin's lymphomas (B-NHL) and a B-NHL cell line. The evidence of a significant proportion of loss-of-function mutations and a complete absence of the normal copy of ATM in the majority of mutated tumours establishes somatic inactivation of this gene in the pathogenesis of sporadic T-PLL and suggests that ATM acts as a tumour suppressor. As constitutional DNA was not available, a putative hereditary predisposition to T-PLL will require further investigation.

Amino Acid Sequence↗
PubMed1997

Lack of specific antibody response in common variable immunodeficiency (CVID) associated with failure in production of antigen-specific memory T cells. MRC Immunodeficiency Group.

Several T cell defects have been described in the antibody deficiency disease, CVID, but there have been few data on the generation of responses of specific T cell populations to primary neoantigens. We have now used immunization with the neoantigens, keyhole limpet haemocyanin (KLH) and DNP-Ficoll, to evaluate immune responses in CVID patients and normal donors. B and T cell responses were examined 2 and 4 weeks post-immunization. Sera were examined for IgM and IgG anti-KLH responses by ELISA and for anti-DNP-Ficoll activity by haemagglutination. The frequency of KLH-responsive T cells was measured by DNA synthesis in a limiting dilution culture system. Low density cells enriched for dendritic cells were pulsed with KLH and cultured with different numbers of autologous T cells. T cells from normal donors and from patients showed a low frequency of antigen-specific precursor T cells (< or = 1:200,000). After KLH immunization the frequency increased in normal donors (1:60,000 and 1:30,000 at 2 and 4 weeks, respectively), while in CVID patients it did not change from the pre-immunization level. The defect may extend to a dysfunction of antigen-specific cells, rather than being solely due to the reduced numbers of cells, since mean responses of 'positive' wells were also reduced. The serum-specific antibody response paralleled the T cell data, in that all normal donors but none of the CVID patients generated IgG KLH-specific antibodies. CVID patients did produce IgM antibodies against the T-independent DNP-Ficoll, but at a lower level than normal controls. These data show that both T and B cells from CVID patients have defective responses to specific antigen, implicating both lineages in the antibody deficiency.

Adult↗
PubMed1997

Mycoplasmal arthritis in patients with primary immunoglobulin deficiency: clinical features and outcome in 18 patients.

A survey of 358 patients with primary antibody deficiency shows that mycoplasmal infection is the commonest cause of severe chronic erosive arthritis. We review our experience with 18 patients with confirmed or probable mycoplasmal arthritis. There was a broad spectrum of severity from a monoarthritis rapidly responding to tetracyclines to severe debilitating polyarthritis, sometimes with antibiotic-resistant organisms which in two cases were eliminated following hyperimmune animal serum therapy. Most patients had very low serum 1gG levels at the onset of arthritis, suggesting that maintaining levels within the normal range with immunoglobulin replacement may prevent infection. The unique susceptibility of these patients to mycoplasmal arthritis shows that antibodies play a crucial role in protection against these organisms.

Adolescent↗
PubMed1996

ATM mutations in cancer families.

Ataxia-telangiectasia (A-T) is a multisystem recessive disease characterized clinically by cerebellar ataxia, oculocutaneous telangiectasias, immunodeficiency, sensitivity to radiomimetic agents, and cancer predisposition. This pleiotropic disorder is caused by mutations in the ATM (mutated in A-T) gene, which is located in the human chromosomal region 11q22-q23. The ATM gene product is a member of a novel family of large proteins implicated in the regulation of the cell cycle and response to DNA damage. Heterozygosity for A-T was previously suggested to be associated with an increased risk of tumors, particularly female breast cancer. Because of loss of constitutional heterozygosity at 11q22-q23 is a frequent event in breast and other tumors, suggesting the presence of a tumor suppressor gene(s) in this region, we screened blood DNA samples from 88 unrelated breast cancer patients of Swedish cancer families for ATM mutations using single-strand conformation polymorphism analysis. All patients had a family history of tumors previously associated with A-T heterozygosity or homozygosity. We demonstrate the first three germ-line mutations in ATM identified by screening of breast cancer patients. Two mutations were previously found in A-T homozygotes and one mutation was a 1-bp insertion. All mutations were found in families with a large number of tumors, however, they did not cosegregate with malignancies. Although the proportion of A-T carriers in this sample seems to be higher than expected by chance, larger studies and pooled data sets will be required to establish that an A-T allele confers cancer susceptibility in heterozygotes.

Adenine↗
PubMed1996

The ATM gene and susceptibility to breast cancer: analysis of 38 breast tumors reveals no evidence for mutation.

Heterozygosity for ataxia-telangiectasia (A-T), a cancer-prone recessive syndrome, has been associated with an increased risk of breast cancer. The gene for A-T (ATM) is located at chromosomal region 11q22-q23, a region of frequent loss of constitutional heterozygosity in breast and other tumors. Loss of constitutional heterozygosity at 1lq22-q23 was found in 47% of informative cases in the series of primary tumors analyzed in this study. To investigate the role of ATM in breast cancer, we have determined the complete genomic organization of the gene, developed an exon-scanning PCR single-strand conformation polymorphism (PCR-SSCP) assay for mutation detection of ATM, and screened 38 consecutive breast tumors for mutations using both genomic DNA- and cDNA-based assays. In addition to common ATM polymorphisms detected both in the coding sequence and in flanking introns, seven unique SSCP alleles were identified in six tumor DNAs. Sequence analysis of these alleles revealed rive nucleotide substitutions that were predicted to change the encoded amino acid. However, PCR-SSCP and nucleotide sequencing analysis of the paired blood samples and of an extended sample size of a total of 224 chromosomes indicated that these SSCP patterns represent constitutional rare polymorphisms with a frequency between 0.005 and 0.023. Because the majority of A-T mutations are null mutations and none of the ATM alleles found in breast cancer samples would lead to the truncation of the translation product, we conclude that, in this initial sample of sporadic breast cancer patients, there was no evidence for an increased number of A-T carriers. In addition, because no somatic mutations were found, our study rules out the ATM gene as the frequently altered tumor suppressor gene at 11q23.

Ataxia Telangiectasia↗
PubMed1996

The molecular basis of hereditary complement factor I deficiency.

The molecular basis of hereditary complement factor I deficiency is described in two pedigrees. In one pedigree, there were two factor I-deficient siblings, one of whom was asymptomatic and the other suffered from recurrent pyogenic infections. Their factor I mRNA was analyzed by reverse transcription of fibroblast RNA followed by amplification using the polymerase chain reaction. Both siblings were homozygous for the same transversion (adenine to thymine) at nucleotide 1282 in the cDNA. This mutation causes histidine-400 to be replaced by leucine. The altered histidine is a semi-conserved residue within the serine proteinase family, although no function has been ascribed to it. The proband of the second pedigree studied was found to be a compound heterozygote. One allele had the same mutation as the first family, the second allele had a donor splice site mutation that resulted in the deletion of the mRNA encoded in the fifth exon (a low-density lipoprotein receptor domain) from its transcript.

Alleles↗
PubMed1996

Common variable immunodeficiency presenting as a Mycoplasma hominis septic arthritis.

A case is reported of common variable immunodeficiency (CVID) presenting as an acute septic arthritis due to Mycoplasma hominis. The diagnosis was not considered until the hypogammaglobulinaemia was discovered and the synovial fluid cultured specifically for mycoplasmas. The importance of diagnosing immunodeficiency states and searching for mycoplasmas in 'bacteriologically culture negative' cases is emphasized.

Adult↗