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Biomedical subjects

M E Conley

Publications and source records attributed to M E Conley.

At least 73 records · Page 4Linked to original sources
PubMed1993

CD40 ligand gene defects responsible for X-linked hyper-IgM syndrome.

The ligand for CD40 (CD40L) is a membrane glycoprotein on activated T cells that induces B cell proliferation and immunoglobulin secretion. Abnormalities in the CD40L gene were associated with an X-linked immunodeficiency in humans [hyper-IgM (immunoglobulin M) syndrome]. This disease is characterized by elevated concentrations of serum IgM and decreased amounts of all other isotypes. CD40L complementary DNAs from three of four patients with this syndrome contained distinct point mutations. Recombinant expression of two of the mutant CD40L complementary DNAs resulted in proteins incapable of binding to CD40 and unable to induce proliferation or IgE secretion from normal B cells. Activated T cells from the four affected patients failed to express wild-type CD40L, although their B cells responded normally to wild-type CD40L. Thus, these CD40L defects lead to a T cell abnormality that results in the failure of patient B cells to undergo immunoglobulin class switching.

Animals↗
PubMed1993

Nonrandom X chromosome inactivation in natural killer cells from obligate carriers of X-linked severe combined immunodeficiency.

X-linked severe combined immunodeficiency (XSCID) is characterized by hypogammaglobulinemia, markedly reduced numbers of T cells, absent mitogen responses, decreased numbers of NK cells, and normal or elevated numbers of B cells. The abnormalities in the NK cell and B cell lineages could be attributed to dependence of these cell lineages on T cells or T cell-derived factors, or to expression of the XSCID gene defect in these cell lineages. In past experiments, we have examined X chromosome inactivation patterns in T cells and cultured B cells from female obligate carriers of XSCID and have found that both cell lineages demonstrate nonrandom X chromosome inactivation. This indicates that the gene defect is intrinsic to both of these cell lineages. In the present experiments, a polymerase chain reaction technique was used to evaluate X chromosome inactivation patterns in highly purified populations of freshly isolated NK cells, B cells, CD4+ cells, and CD8+ cells from three obligate carriers of XSCID. All four lymphoid cell populations from these three women exhibited exclusive use of a single X as the active X. In contrast, both X chromosomes were used as the active X in neutrophils and monocytes. These findings indicate that the XSCID gene is expressed in the NK cell lineage as well as in T cells and B cells. This observation makes it highly unlikely that the XSCID gene is involved in Ag receptor gene rearrangements.

B-Lymphocytes↗
PubMed1993

Linkage analysis and physical mapping near the gene for X-linked agammaglobulinemia at Xq22.

The gene for X-linked agammaglobulinemia (XLA) has been mapped to Xq22. No recombinations have been reported between the gene and the probe p212 at DXS178; however, this probe is informative in only 30-40% of women and the reported flanking markers, DXS3 and DXS94, are 10-15 cM apart. To identify additional probes that might be useful in genetic counseling, we examined 11 polymorphisms that have been mapped to the Xq21.3-q22 region in 13 families with XLA. In addition, pulsed-field gel electrophoresis and yeast artificial chromosomes (YACs) were used to further characterize the segment of DNA within which the gene for XLA must lie. The results demonstrated that DXS366 and DXS442, which share a 430-kb pulsed-field fragment, could replace DXS3 as proximal flanking markers. Probes at DXS178 and DXS265 identified the same 145-kb pulsed-field fragment, and both loci were contained within a 200-kb YAC identified with the probe p212. A highly polymorphic CA repeat (DXS178CA) was isolated from one end of this YAC and used in linkage analysis. Probes at DXS101 and DXS328 shared several pulsed-field fragments, the smallest of which was 250 kb. No recombinations were seen between XLA and the DXS178-DXS265-DXS178CA complex, DXS101, DXS328, DXS87, or the gene for proteolipid protein (PLP). Key crossovers, when combined with the linkage data from families with Alport syndrome, suggested the following order of loci: cen-DXS3-DXS366-DXS442-(PLP, DXS101, DXS328, DXS178-DXS265-DXS178CA complex, XLA)-(DXS87, DXS94)-DXS327-(DXS350, DXS362)-tel.(ABSTRACT TRUNCATED AT 250 WORDS)

Agammaglobulinemia↗
PubMed1993

Refinement of linkage of human severe combined immunodeficiency (SCIDX1) to polymorphic markers in Xq13.

The most common form of human severe combined immunodeficiency (SCID) is inherited as an X-linked recessive genetic defect, MIM 300400. The disease locus, SCIDX1, has previously been placed in Xq13.1-q21.1 by demonstration of linkage to polymorphic markers between DXS159 and DXS3 and by exclusion from interstitial deletions of Xq21.1-q21.3. We report an extension of previous linkage studies, with new markers and a total of 25 SCIDX1 families including female carriers identified by nonrandom X chromosome inactivation in their T lymphocytes. SCIDX1 was nonrecombinant with DXS441, with a lod score of 17.96. Linkage relationships of new markers in the SCIDX1 families were consistent with the linkage map generated in the families of the Centre d'Etude du Polymorphisme Humain (CEPH) and with available physical map data. The most likely locus order was DXS1-(DXS159,DXS153)-DXS106-DXS132-DXS4 53-(SCIDX1,PGK1, DXS325,DXS347,DXS441)-DXS447-DXS72-DXYS 1X-DXS3. The SCIDX1 region now spans approximately 10 Mb of DNA in Xq13; this narrowed genetic localization will assist efforts to identify gene candidates and will improve genetic management for families with SCID.

Dosage Compensation, Genetic↗
PubMed1992

Atypical Wiskott-Aldrich syndrome in a girl.

Wiskott-Aldrich syndrome (WAS) is a fully penetrant X-linked recessive disorder characterized by thrombocytopenia with small platelets, eczema, and defects of both T-cell and B-cell immunity. Obligate carriers of this disorder show no signs of the gene defect because in the cell lineages primarily affected by the disorder they demonstrate preferential use of the normal, nonmutant X as the active X. This can be explained by the selective disadvantage in proliferation and/or survival experienced by the cells with the mutant X as the active X. We have recently evaluated an 8-year-old girl with a disorder phenotypically identical to WAS. Cytogenetic studies did not show any structural abnormalities of the X chromosome and X chromosome inactivation analysis showed that both of her X chromosomes could function as the active X. These findings suggest that there is an autosomal recessive disorder that is very similar to classic WAS.

Antigens, CD↗
PubMed1992

Females with a disorder phenotypically identical to X-linked agammaglobulinemia.

Clinical and laboratory findings in two girls with a disorder phenotypically indistinguishable from typical X-linked agammaglobulinemia (XLA) are described. To examine the possibility that subtle defects in the X chromosome might explain the findings, detailed genetic studies were performed on one of these patients. Cytogenetic studies showed a normal 46XX karyotype. Southern blot analysis of her DNA showed that she had inherited a maternal and a paternal allele at sites flanking the locus for typical XLA at Xq22, making a microdeletion or uniparental disomy unlikely. To determine whether both of her X chromosomes could function as the active X, somatic-cell hybrids that selectively retained the active X were produced from her activated T cells. A normal random pattern of X inactivation was seen. Of 21 T-cell hybrids, 3 retained both X chromosomes, 7 had one X as the active X, and 11 had the other X as the active X. We have interpreted these studies as indicating that there is an autosomal recessive disorder that is phenotypically identical to XLA.

Agammaglobulinemia↗
PubMed1992

Genetic immunodeficiencies: both the lumpers and the splitters can claim victory.

Over the last few years, molecular approaches to analysis of genetic immunodeficiencies have made it clear that different mutations of the same gene may result in very different clinical presentations. On the other hand, a single clinical syndrome is sometimes due to mutations in a variety of independent genes. In the future, appropriate treatment, particularly gene therapy, will depend on a precise genetic diagnosis.

Agammaglobulinemia↗
PubMed1992

Molecular approaches to analysis of X-linked immunodeficiencies.

Although the X-linked immunodeficiencies--X-linked agammaglobulinemia (XLA), X-linked severe combined immunodeficiency (XSCID), Wiskott-Aldrich syndrome (WAS), X-linked lymphoproliferative syndrome and X-linked hyper IgM syndrome--have been mapped to loci distributed throughout the X chromosome, they have several features in common that suggest that they might be members of a gene family: (i) all are maintained in the population at approximately the same gene frequency; (ii) expression of each defect is limited to the hematopoietic system; (iii) atypical forms of each disorder have been described; and (iv) obligate carriers of these disorders are normal by all immunologic criteria. The failure of carriers of XLA, XSCID, and WAS to show signs of their gene defects can be explained by the preferential use of the normal, nonmutant X as the active X in the cell lineages affected by the gene defects. These three disorders also share an additional feature; in boys with XLA, XSCID, or WAS there is asynchronous expression of cell surface markers of differentiation or activation. If some or all of the genes that are abnormal in the X-linked immunodeficiencies are members of a gene family, then isolation of one gene may lead to the others.

Dosage Compensation, Genetic↗
PubMed1991

Retrospective analysis of the incidence of pulmonary disease in hypogammaglobulinemia.

To determine the best predictors of chronic pulmonary disease in patients with hypogammaglobulinemia, we evaluated the clinical records, chest x-ray films, and pulmonary function tests of 10 patients with X-linked agammaglobulinemia (XLA) followed for a mean of 12.5 years, and 12 patients with common variable immunodeficiency (CVID) followed for a mean of 10.5 years. These patients, most of whom were treated with intramuscular gamma globulin and long-term oral antibiotics, had very few pneumonias after diagnosis. The patients with XLA had 0.10 pneumonias per treatment year, and the patients with CVID had 0.18 pneumonias per treatment year. Seven of the 10 patients with XLA had normal chest x-ray films 8 to 15 years after diagnosis, and none had bronchiectasis. Pulmonary disease was more common and more severe in the group with CVID, but five patients in this group also had normal chest x-ray films after long follow-up. In the entire group of 22 patients, nine of the 10 patients with abnormal chest x-ray films on most recent evaluation already had pulmonary disease at the initial visit (p = 0.00002). These studies indicate that the best predictors of good pulmonary function in patients with hypogammaglobulinemia are early diagnosis and good compliance with gamma globulin replacement therapy and oral antibiotics.

Agammaglobulinemia↗
PubMed1991

Molecular analysis of X-linked agammaglobulinemia with growth hormone deficiency.

To address the relationship between the gene (or genes) that causes the syndrome of X-linked hypogammaglobulinemia with isolated growth hormone deficiency and the gene responsible for typical X-linked agammaglobulinemia (XLA), we have used cytogenetics, examination of X chromosome inactivation patterns in potential carriers of the defect, and linkage analysis to study two unrelated families in which the affected males had isolated growth hormone deficiency and immunologic findings indistinguishable from those of typical XLA. A deletion could not be demonstrated in either family by G-banded karyotypes or flow cytometric analysis of metaphase chromosomes. Studies of X inactivation showed that mothers of affected boys from both families exhibited selective use of a single X chromosome as the active X chromosome in B cells but not T cells. This pattern is the same as that seen in obligate carriers of typical XLA. Linkage analysis demonstrated the most likely location for this gene (or genes) to be the midportion of the long arm of the X chromosome between DXS3 and DXS94. This segment of the X chromosome, which constitutes approximately 5% of the total X chromosome, encompasses the gene for XLA. These findings are consistent with the combination of XLA and growth hormone deficiency being caused by a small, contiguous, gene deletion syndrome involving the gene for XLA or an allelic variant of the gene for typical XLA.

Agammaglobulinemia↗
PubMed1991

X-linked severe combined immunodeficiency.

Between a third and half of all males with SCID and no family history of immunodeficiency represent the first manifestation in their family of a new mutation of the gene that causes X-linked SCID. These patients, like boys with a positive family history of X-linked SCID, have markedly reduced numbers of T cells, elevated numbers of B cells, and hypogammaglobulinemia. The hypogammaglobulinemia is due, at least in part, to the expression of the gene defect in B cells as well as in T cells. Patients with X-linked SCID who are treated with bone marrow transplant tend to engraft T cells readily but they do not engraft B cells unless they are treated with cytoreductive therapy prior to transplant. B-cell function after transplant tends to be poor, even in patients who have received transplants from HLA matched siblings. Better transplant strategies are required to achieve optimum long-term results in patients with X-linked SCID.

Bone Marrow Transplantation↗
PubMed1990

Atypical presentation of Wiskott-Aldrich syndrome: diagnosis in two unrelated males based on studies of maternal T cell X chromosome inactivation.

Congenital thrombocytopenia may occur in isolation or accompanied by eczema and immunodeficiency, as part of the X-linked hereditary Wiskott-Aldrich syndrome (WAS). Because the clinical and immunologic picture of WAS is variable, particularly early in life, definite diagnosis cannot always be made in cases with a negative family history. Two unrelated males with sporadic congenital thrombocytopenia had only questionable immunologic abnormalities as infants, making them clinically indistinguishable from cases of isolated thrombocytopenia, although one developed episodic neutropenia and the other began to manifest a multisystem autoimmune disease at 2 years of age. Evaluation of X chromosome inactivation in the T cells of both patients' mothers showed each of these women to have the same highly skewed X chromosome inactivation pattern seen in carriers of typical familial WAS. A T-cell defect was subsequently directly demonstrated in the second patient, whose lymphocytes failed to proliferate to periodate and anti-CD43. Taken together, these data suggest the presence of T cell immunodeficiency consistent with WAS in these patients. Furthermore, their mothers were found to have a very high likelihood of being carriers, lending support to the diagnosis of a hereditary disease in these boys and making possible genetic prediction in other family members and subsequent pregnancies.

Dosage Compensation, Genetic↗
PubMed1990

X chromosome inactivation patterns in obligate carriers of X-linked lymphoproliferative syndrome.

To determine whether the gene defect that causes X-linked lymphoproliferative syndrome (XLP) results in a selective disadvantage in proliferation or survival of leukocytes, we analyzed X chromosome inactivation patterns in neutrophils, T cells, and B cells from two unrelated obligate carriers of XLP. Analysis of DNA methylation patterns and production of somatic cell hybrids demonstrated that all three cell lines from both women exhibited normal, random X chromosome inactivation. These findings indicate that the XLP gene defect does not result in a global defect in proliferation or survival of T cells or B cells. It remains possible that a subset of T or B cells or natural killer cells may be selectively affected. It is also possible that the gene defect alters function but not proliferation or survival of T or B cells.

B-Lymphocytes↗
PubMed1990

X-linked severe combined immunodeficiency. Diagnosis in males with sporadic severe combined immunodeficiency and clarification of clinical findings.

Over 80% of infants with severe combined immunodeficiency (SCID) of unknown genetic etiology are males, yet less than a third of these affected males have a family history of X-linked disease. To help identify new mutations of the X-linked SCID gene and to provide genetic counseling, X chromosome inactivation patterns in T cells from 16 women who had sons with sporadic SCID were examined. Between 9 and 35 human/hamster hybrids that selectively retained the active human X chromosome were produced from the T cells of each woman and analyzed with an X-linked restriction fragment length polymorphism for which the woman in question was heterozygous. Exclusive use of a single X as the active X was seen in the T cell hybrids from 7 of the 16 women, identifying these women as carriers of X-linked SCID. Studies on additional family members confirmed the mutant nature of the inactive X and revealed the source of the new mutation in three families. To determine whether there were any laboratory characteristics that might differentiate the boys whose mothers were identified as carriers of X-linked SCID from those whose mothers were not, the clinical records of both groups were compared to each other and to a group of 14 boys with a family history of X-linked SCID. The most consistent finding in the 21 patients with X-linked SCID was an elevated proportion of B cells. These data demonstrate the high incidence of spontaneous mutation for the X-linked SCID gene and help clarify the characteristic presenting features of this disorder.

B-Lymphocytes↗