Genetic heterogeneity of the hexosaminidase deficiency diseases.
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Cytotoxic effectors-CD8+ T cells protect hosts against cytopathic viruses. CD8+ T cell mediated lysis of host cells infected with non-cytopathic viruses may lead to tissue disease causing damage as is the case in hepatitis B virus infections in men or lymphocytic choriomeningitis virus (LCMV) infections in mice. In a mouse model it was demonstrated that virus induced immunodeficiency by LCMV was not caused by the virus directly but rather by immunopathological consequences of anti-LCMV CD8+ T cells destroying LCMV-infected antigen-presenting cells and macrophages. These results may suggest that HIV induced immunodeficiency could similarly be caused by immunopathology because 1. HIV has not been demonstrated to be cytopathic in vivo. 2. CD8+ T cells control HIV infection efficiently for a longtime and 3. only few CD4+ T cells but many macrophages, monocytes and dendritic cells are productively HIV infected. Therefore AIDS may be the result of specific CD8+ T cells destroying antigen presenting cells and effector/macrophages/monocytes thereby causing immunosuppression and inability to control intracellular infections. Compared to the view that HIV is cytopathic, the immunopathological view of AIDS suggests obviously different vaccine and therapy strategies.
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Cancer development requires the accumulation of numerous genetic changes which are usually believed to occur through the presence of unrepaired DNA lesions. Exogenous or endogenous DNA-damaging agents can lead to mutations in the absence of efficient error-free repair, via replication of DNA damage. Several DNA repair pathways are present in living cells and well conserved from bacteria to human cells. Apart from mismatch repair, photolyases, base excision, and postreplication repair, the nucleotide excision repair (NER), the most versatile of these DNA repair systems, recognizes and eliminates a wide variety of DNA lesions and particularly those induced by ultraviolet (UV) light. The phenotypic consequences of an NER defect in humans are apparent in rare but dramatic diseases characterized by hypersensitivity to UV and a striking clinical and genetic heterogeneity. The xeroderma pigmentosum syndrome (XP), the Cockayne's syndrome (CS), and the photosensitive form of trichothiodystrophy (TTD) are three of these clinically distinct human disorders inherited as an autosomal recessive trait. Persistence of unrepaired DNA damage produced by exposure to UV light is associated, in the XP syndrome, with an extremely high level of skin tumors in sun-exposed sites. But the direct link of defective DNA repair to cancer seems to be complex, since, in contrast to patients with XP, those with TTD or CS do not have an increased frequency of skin cancers. The understanding of the absence of skin tumors in TTD and CS patients may offer a way to better protect normal individuals from the most rapidly increasing cancer: skin cancer.
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To conclude, an impairment of the NO synthase pathway may be one of the earliest events in atherogenesis. A reduction in NO synthesis and/or activity may contribute to the initiation and progressive of atherosclerosis. Derangement of the NO synthase pathway may occur by several mechanisms, including lipoproptein-induced alterations in signal transduction; increases in superoxide anion elaboration (and degradation of NO); reduced affinity of NOS for L-arginine; and/or elevated levels of circulating antagonists. NO is a potent vasodilator, a regulator of vascular structure, and an inhibitor of endothelial interactions and circulating blood elements. A loss of endothelial NO activity may contribute to the abnormal vasomotion observed in coronary artery disease, as well as the progression of atherosclerosis. Strategies to enhance NO synthesis and/or activity may be useful in maintaining cardiovascular health.
Deficiency of any of the vitamins and minerals essential for normal erythropoiesis (haematinics), including iron, copper, cobalt, vitamins A, B12, B6, C, E, folic acid, riboflavin and nicotinic acid, may be associated with defective erythropoiesis and anaemia. Iron, vitamin B12 and folate are the haematinics for which deficiency states manifest most often clinically and are the focus of this review. The normal absorption of these haematinics and gastrointestinal causes of their deficiency are described. Investigations, including the use of homocysteine metabolite levels and new techniques such as serum transferrin receptor assays, and treatment of haematinic deficiency are discussed in detail.
Deficiency of apolipoprotein can be of genetic origin or due to diseases like advanced chronic liver disease. Deficiency of apolipoprotein A causes Tangier disease without any major hepatic involvement being reported. Deficiency of apolipoprotein B causes abetalipoproteinemia or familial hypobetalipoproteinemia; with hepatic involvement in the form of raised transaminases, fatty liver and cirrhosis. Advanced chronic liver disease itself can cause reduction of apolipoprotein A and apolipoprotein B levels and acanthocytosis. In patients with chronic liver disease of undetermined etiology, lipid profile and apolipoprotein levels should be obtained routinely. If it suggests apolipoprotein B deficiency, then liver biopsy can be avoided, as the etiology of chronic liver disease is established. Isolated deficiency of either apolipoprotein A or apolipoprotein B suggests etiology of chronic liver disease, while deficiency of both apolipoprotein A and apolipoprotein B is a manifestation of advanced chronic liver disease.
Defect in degradation of blood group B-immunoactive glycosphingolipids in Fabry disease (deficiency of lysosomal alpha-galactosidase EC 3.2.1.22) has been studied using highly sensitive and specific TLC-immunostaining analysis of urinary sediments and tonsillar tissues of blood group B patients and healthy controls, secretors and nonsecretors. The B glycolipid antigens with hexasaccharide chains were consistently found increased (25- to 100-fold) in the urinary sediments of three Fabry patients, blood group B or AB secretors. Conversely, they were absent in the urinary sediment of one blood group B nonsecretor patient. In normal secretors, B glycosphingolipids were present only in traces. Moreover, significant increase in B glycolipid antigens (8-fold) was found in the tonsillar tissue of a Fabry patient blood group B secretor. We conclude that the secretor status is responsible for increased concentration of blood group B glycosphingolipids in both urinary cells and tonsils in alpha-galactosidase deficiency. The quantity of stored B-immunoactive glycosphingolipids, however, is much lower than that of the mainly accumulated glycosphingolipid Gb(3)Cer. The results clearly indicate that active or silent Se gene, which controls synthesis of B-antigen precursors, is responsible for notable difference in B-glycosphingolipids expression in Fabry patients - secretors and nonsecretors. Whether this novel aspect may be of prognostic significance, remains to be established.
Complement deficiency is associated with an increased prevalence of pyogenic infections and immune complex disease. The spectrum of disease in deficient individuals depends on the stage in the complement system at which the block in activation occurs. Here, Paul Morgan and Mark Walport review current knowledge of hereditary complement deficiencies in humans, emphasizing the importance of these 'experiments of nature' in defining the roles of complement in vivo.