Carrier detection of the X-linked primary immunodeficiency diseases using X-chromosome inactivation analysis

Carrier detection of three of the X-linked primary immunodeficiency diseases (X-linked agammaglobulinemia, X-linked severe combined immunodeficiency disease, and the Wiskott-Aldrich syndrome) is possible by analyzing patterns of X-chromosome inactivation in those cells affected by the disorder. Normal women have balanced patterns of X-chromosome inactivation; that is, in a given population of cells, approximately half of their active X chromosomes are of paternal origin and half of their active X chromosomes are of maternal origin. In contrast, female carriers of these X-linked immunodeficiency disorders have an unbalanced pattern of X-chromosome inactivation in those cell lineages that are affected by the disorder; that is, all the active X chromosomes in affected cell lineages are the X chromosomes that carry the normal allele. Two techniques are available for X-chromosome inactivation analysis. One technique depends on methylation differences between the active and inactive X chromosome, and the other technique uses somatic cell hybrids that selectively retain the active X chromosome. In either case, carrier detection can be performed in individuals from families in which only one member of the family has been affected, since neither of these methods depends on linkage analysis.     

Genetics of menopause-associated diseases.

Menopause is the permanent cessation of menstruation resulting from the loss of ovarian follicular activity. It is estimated that perhaps 50 million women worldwide will go into menopause annually. Atherosclerotic cardiovascular disease, osteoporotic fractures and Alzheimer's dementia are common chronic disorders after menopause, representing major health problems in most developed countries. Apart from being influenced by environmental factors, these chronic disorders recognize a strong genetic component, and there are now considerable clinic evidences that these disorders are related to low hormonal milieu of postmenopausal women. Here, we review up-to-date available data suggesting that genetic variation may contribute to higher susceptibility to four sporadic chronic syndromes such as osteoporosis (OP), osteoarthritis (OA), Alzheimer's disease (AD) and coronary artery disease (CAD). For these four syndromes candidate genes that today appear as major loci in genetic susceptibility encode for proteins specific of a given system, as the vitamin D receptor (VDR) gene for the skeleton and, therefore, OP or angiotensin converting enzyme (ACE) for the cardiovascular system and, therefore, CAD. The investigation of gene polymorphisms in various pathological conditions typical of postmenopause offer an explanation not only of their genetic inheritance but also of their co-segregation in given individuals. In this view, it may be possible to identify a common set of genes whose variants contribute to a common genetic background for these different disorders. Ideal candidates appear genes of the estrogen response cascade [i.e. estrogen receptor (ERs), enzymes involved in estrogen metabolism or co-activators and co-inhibitors]. All together this information may represent the basis both for future recognition of individuals at risk and for the pharmacogenetic driving of drug responsiveness.     

Antibody-dependent lymphocyte killer function in human immunodeficiency diseases.

Antibody-dependent cell immunity to the lymphocyte system (ABCIL) has been shown to be a function of a non-thymus-processed cell in the experimental animal. To evaluate its role in the human and to assess its clinical usefulness, we assessed ABCIL in twenty-five patients with various immunodeficiency (ID) syndromes. Our technique measures the lysis of 51Cr-labelled normal human lymphocytes coated with HL-A-specific antibody. Cytotoxicity is expressed as a percentage of 51Cr released after subtracting the spontaneous target cell release. Mean values in normals are 20+/-2 (s.e.). The ten patients with AB deficiency had a mean ABCIL of 7-9+/-2 (Pless than0-01). All eight patients with cellular ID had normal ABCIL (18+/-2), while the ten patients with combined ID had variable results. Effector cell function in the ABCIL test correlated (r=0-74; Pless than0-05) with the percentage of B cells in the peripheral blood. No correlation was found between ABCIL function and serum immunoglobulin levels or rosette-forming cells in the peripheral blood. There is a function for B lymphocytes other than as a precursor of antibody-synthesizing cells.     

Canine X-linked severe combined immunodeficiency

Our laboratory has identified and characterized an X-linked severe combined immunodeficiency (XSCID) in dogs that is due to mutations in the common gamma (γc) subunit of the interleukin-2 (IL2), IL4, IL7, IL9, and IL 15 receptors. Canine XSCID, unlike genetically engineered γc-deficient mice, has a clinical and immunologic phenotype virtually identical to human XSCID. It appears that speciesspecific differences exist in the role of the γc and its associated cytokines in mice compared to their role in humans and dogs, suggesting γc-deficient dogs may be a more relevant model for studing the role of the γc in humans. We are utilizing this model for a variety of studies to address:

1. Fundamental questions concerning the role of the γc in cytokine regulation and lymphocyte development.
2. The pathogenesis of XSCID.
3. Strategies for improving bone marrow transplantation outcome.
4. Development and evaluation of strateies for gene therapy.
5. Human hematopoietic stem cell development.

     

Animal models for immunodeficiency diseases.

Immunodeficient animals continue to provide insights into the development and function of the immune system. These animals also serve as models for the propagation of normal and malignant human cells and as hosts for infectious agents, including HIV. New developments in basic and applied research using immunodeficient animals were discussed at a recent workshop.     

Abnormal development of thymic dendritic and epithelial cells in human X-linked severe combined immunodeficiency

The X-linked form of severe combined immunodeficiency (X-SCID) is caused by mutations in the common cytokine receptor gamma chain and results in lack of T and NK cells and defective B cells. Without immune reconstitution, X-SCID patients typically die from infection during infancy. This report describes thymic epithelial (TE), lymphocyte, and dendritic cell (DC) differentiation in the thymic microenvironment of seven X-SCID patients who died before or after treatment for their immunodeficiency. X-SCID thymus consisted predominately of TE cells without grossly evident corticomedullary distinction. CD3+ and CD1a+ developing T cells and CD83+ thymic DC were reduced >50-fold when compared to age- and gender-matched control thymus (P < 0.001). TE expression of epithelial differentiation markers CK14, involucrin, and high molecular weight cytokeratins also differed in X-SCID versus normal thymus. These histopathologic findings indicate that in addition to T cells, thymic DC development and differentiation of TE cells are also abnormal in X-SCID.     

X-linked diseases and carrier detection

Advances in molecular biology applied to the location of genes have generated a real evolution for the screening of women carrying X-related diseases. It is however imperative to first try to define the status of these women using classical methods: bayesian calculations taking into account genealogical data and direct screening which is partially reliable because of the inactivation of an X chromosome in women. The new genetic engineering techniques enable to locate the gene in an affected patient and follow its transmission in the families with the use of tracers linked to the gene of the disease. The difficulties of these studies are due to two phenomena. First, the risk of allele recombination because of a crossing over during the mitosis. This risk must be computed and specified. The second phenomenon is related to variations of information in the families which may either completely prevent identification of the carriers, or give less reliable results. The increasing number of molecular probes should enable to resolve this problem.     

X-linked severe combined immunodeficiency in the dog

This study documents the occurrence of a form of X-linked severe combined immunodeficiency (SCID) in the dog with clinical, immunologic, and pathologic features similar to those of X-linked SCID with B cells in man. The disease in the dog is characterized by growth retardation and increased susceptibility to bacterial and viral infections in young pups. Affected pups have all died or were euthanatized by 5 months with signs of canine distemper, infectious hepatitis, or bacterial pneumonia. Laboratory findings include normal numbers of circulating B lymphocytes and normal concentrations of serum IgM, but low to absent concentrations of serum IgG and IgA, indicating a defect in the terminal differentiation of IgG and IgA B cells into immunoglobulin-secreting plasma cells. This is supported by the failure of peripheral lymphocytes to produce IgG or IgA plaque-forming cells in response to polyclonal activation. There are low-to-normal numbers of circulating T cells, but a severely depressed blastogenic response to T cell mitogens. Postmortem findings include thymic dysplasia and hypoplasia of lymphoid tissue. Family studies and breeding experiments are consistent with an X-linked recessive mode of inheritance.     

X-linked diseases: susceptible females

The role of X-inactivation is often ignored as a prime cause of sex differences in disease. Yet, the way males and females express their X-linked genes has a major role in the dissimilar phenotypes that underlie many rare and common disorders, such as intellectual deficiency, epilepsy, congenital abnormalities, and diseases of the heart, blood, skin, muscle, and bones. Summarized here are many examples of the different presentations in males and females. Other data include reasons why women are often protected from the deleterious variants carried on their X chromosome, and the factors that render women susceptible in some instances.     

Postnatal development of T lymphocytes in a novel X-linked immunodeficiency disease.

We previously reported an X-linked combined immunodeficiency disease (CID) characterized by immune deficiencies and complicating infections that were more moderate than those found in severe CID (SCID). Since other unstudied males in the family died in infancy, we questioned whether this T cell defect was more profound in early life. Subsequently, the development of blood T cells in an affected newborn male was examined. T cells were virtually undetectable at 48 hr. Over the next several months, CD4+ T cells (principally CD45RO+) rose to levels similar to those found in older affected males, but CD8+ T cells developed more slowly and never attained levels found in other affected males. Thus, this disease in early life mimics SCID and may pose a higher risk of fatal infections to affected individuals during that period. Finally, we speculate that the genetic defect may disrupt intrathymic development or selection of T cells.     

B cell developmental defects in X-linked immunodeficiency

We describe an analysis of early B cell development in micewith X linked immunodeficiency (Xid). It was found that, comparedwith the normal CBA/J strain, CBA/N (Xid/Xid) pre-B cells showan increased proliferative response to IL-7 but a decreasedability for subsequent maturation on stromal cells. However,the addition of mast cell growth factor largely restored theability to mature in the presence of stromal cells. No anomalieswere found in the rate of lg eavy or light chain gene rearrangementin CBA/N cells despite their failure to undergo maturation.This suggests that these two events may occur independently.     

Genetics of human brain oscillations.

In the last three decades, much emphasis has been placed on neural oscillations in vitro, in vivo, as well as in the human brain. These brain oscillations have been studied extensively in the resting electroencephalogram (EEG), as well as in the underlying evoked oscillations that make up the event-related potentials (ERPs). There are several approaches to elucidate the possible mechanisms of these brain oscillations. One approach is to look at the neurophysiology and neurochemistry involved in generating and modulating these oscillations. Another more recent approach is to examine the genetic underpinnings of these neural oscillations. It is proposed that the genetic underpinnings of these oscillations are likely to stem from regulatory genes which control the neurochemical processes of the brain, and therefore influence neural function. Genetic analyses of human brain oscillations may identify genetic loci underlying the functional organization of human neuroelectric activity. Brain oscillations represent important correlates of human information processing and cognition. They represent highly heritable traits that are less complex and more proximal to gene function than either diagnostic labels or traditional cognitive measures. Therefore these oscillations may be utilized as phenotypes of cognition and as valuable tools for the understanding of some complex genetic disorders. Genetic loci that have been recently identified regarding both resting and evoked brain oscillations involving the GABAergic and cholinergic neurotransmitter systems of the brain are discussed. It is concluded that the advent of genomics and proteomics and a fuller understanding of gene regulation will open new horizons on the critical electrical events so essential for human brain function.