Genetic prediction in X-linked agammaglobulinaemia

Dendritic and T cell response to influenza is normal in the patients with X-linked agammaglobulinemia

Introduction

Influenza virus is a potential cause of severe disease in the immunocompromised. X-linked agammaglobulinemia (XLA) is a primary immunodeficiency characterized by the lack of immunoglobulin, B cells, and plasma cells, secondary to mutation in Bruton’s tyrosine kinase (Btk) gene. Btk is expressed in both B and dendritic cells (DC). However, little is known about the immune response of DC and T cells to influenza virus in XLA patients.

Methods

The in vitro maturation and antigen presenting function of monocyte-derived immature DC (imDC) from 12 XLA patients and 23 age-matched normal controls in response to influenza virus were examined. Influenza virus-specific CD4 and CD8 T cell responses in the patients and controls were further determined after administration of inactivated trivalent influenza vaccine.

Results

imDC from XLA patients had normal maturation based on major histocompatibility complex (MHC)-I, MHC-II, CD83 and CD86 expression, and interferon (IFN)-α and interleukin-12 production upon influenza virus stimulation. They also had a normal capacity to induce allogeneic T cell proliferation in response to influenza virus. TIV was well tolerated in XLA patients. Influenza virus-specific CD4⁺IFN-γ⁺ and CD8⁺ IFN-γ⁺ T cells and HLA-A2/M1_58–66-tetramer⁺ CTLs could be induced by TIV in XLA patients, and the levels and duration of maintaining these virus-specific cells in XLA patients are comparable to that in normal controls.

Conclusion

We demonstrated for the first time that XLA patients have fully competent DC and T cell immune responses to influenza virus. TIV is safe and could be an option for providing T cell-mediated protection against influenza virus infection in XLA patients.

Non-allelic heterogeneity of familial adenomatous polyposis

Linkage studies on familial adenomatous polyposis (FAP) reported so far suggest that FAP is a genetically homogeneous disease. Recently, we found that the putative gene for Turcot syndrome, an apparently autosomal recessive clinical variant of FAP, is not allelic to FAP. Here we describe another family, segregating for an autosomal dominant disease clinically indistinguishable from FAP but genetically not linked to the APC locus, adding further evidence for the occurrence of non-allelic heterogeneity of FAP. These observations have implications to the linkage-based genetic counselling of persons at risk for FAP especially when they are drawn from small families giving insufficient information.

X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) patients manifest a very low production of immunoglobulins (Ig) of all classes and plasma cells are virtually absent. The XLA gene plays a crucial role in the transition of pre-B cells to later B cell stages, as hardly any slg-positive B lymphocytes can be detected. In the bone marrow almost normal numbers of pre-B lymphocytes are present. These cytoplasmatic C mu+ pre-B lymphocytes appear to express truncated M heavy chain molecules lacking the variable region segment. The T lymphocyte compartment is intact: the numbers of mature T cell receptor (TcR) alpha beta expressing T lymphocyte populations and their proliferative responses to antigens are normal. That the B cells are primary and exclusively affected was proven by X-chromosome inactivation studies. There is no evidence that the XLA gene is directly involved in the Ig gene rearrangements since B lymphoblastoid cell lines (BLCLs) established from peripheral blood of XLA patients were found to produce IgM molecules composed of complete Ig heavy and light chains and were shown to contain normal VHDJH recombinations. The data do not exclude the involvement of the XLA gene in a B cell specific process that makes the Ig loci accessible for recombination. Investigations on the degree of diversity of immunoglobulins generated by XLA patients exposed no limitations in the VH family usage. Sequence analysis of expressed VH3 and VH4 rearrangements however revealed that some genetic elements of the Ig locus might be over-represented and that a high portion of rearrangements was generated by unconventional mechanisms. By restriction length polymorphism (RFLP) and pulsed field gel electrophoreses analyses the XLA gene was mapped to an 8- to 12-Mb DNA fragment located in the Xq22 region. The known location of the XLA gene on the X-chromosome with closely linked RFLP markers and the availability of X-chromosome inactivation assays provides methods for carrier detection and prenatal diagnosis.

Chronic granulomatous disease: a different pattern in Hong Kong?

From July 1988 to December 1989, six boys with chronic granulomatous disease were diagnosed in our institutions. Their clinical features were reviewed in order to delineate the pattern of infections which seems to have both similarities and differences when compared with published reports of Caucasian patients. The most striking differences was the lack of skin sepsis and chronic lymphadenitis in our six patients. Gram-negative organisms were the commonest pathogens while Staphylococci sp. were not isolated. Clinical features which should alert one to the diagnosis were also highlighted. Prophylactic co-trimoxazole was effective in reducing the frequency of bacterial infections. Early diagnosis is not only essential for optimal patient management but also for genetic counselling for the extended family.

Genetics of human X-linked immunodeficiency diseases

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Congenital agammaglobulinemia presenting with ecthyma gangrenosum

Two males with presumed X-linked agammaglobulinemia (X-LA) presented with ecthyma gangrenosum. This is an unusual presentation of this syndrome. Possible causes are discussed.

Identification of a closely linked DNA marker, DXS178, to further refine the X-linked agammaglobulinemia locus

X-linked agammaglobulinemia (XLA) is an inherited recessive disorder in which the primary defect is not known and the gene product has yet to be identified. Utilizing genetic linkage analysis, we previously localized the XLA gene to the map region of Xq21.3-Xq22 with DNA markers DXS3 and DXS17. In this study, further mapping was performed with two additional DNA probes, DXS94 and DXS178, by means of multipoint analysis of 20 families in which XLA is segregating. Thirteen of these families had been previously analyzed with DXS3 and DXS17. Three crossovers were detected with DXS94 and no recombinations were found between DXS178 and the XLA locus in 9 informative families. Our results show that XLA is closely linked to DXS178 with a two-point lod score of 4.82 and a multipoint lod score of 10.24. Thus, the most likely gene order is DXS3-(XLA,DXS178)-DXS94-DXS17, with the confidence interval for location of XLA lying entirely between DXS3 and DXS94. In 2 of these families, we identified recombinants with DXS17, a locus with which recombination had not previously been detected by others in as many as 40 meiotic events. Furthermore, DXS178 is informative in both of these families and does not show recombination with the disease locus. Therefore, our results indicate that DXS178 is linked tightly to the XLA gene.

Evidence for male X chromosomal mosaicism in X-linked agammaglobulinemia

X-Linked agammaglobulinemia (XLA) is a severe antibody deficiency disease in man, resulting from an arrest in differentiation of pre-B cells. XLA is recessive: female carriers do not exhibit antibody deficiency, but manifest an exclusive inactivation of the XLA-carrying X chromosome in all peripheral blood B lymphocytes. An exclusive inactivation of the paternal X chromosome in the B lymphocytes of all daughters of a male who had no agammaglobulinemia demonstrated that the XLA defect can originate from healthy males. These males are X chromosomal mosaics. X-Chromosomal RFLP segregation analyses in other XLA pedigrees suggest a frequent introduction of XLA by healthy males. This implies that XLA often originates from mitotic errors, either at postmeiotic or early postzygotic stages.