Alzheimer's disease is a leading cause of morbidity and mortality among the elderly. Several families have been described in which Alzheimer's disease is caused by an autosomal dominant gene defect. The chromosomal location of this defective gene has been discovered by using genetic linkage to DNA markers on chromosome 21. The localization on chromosome 21 provides an explanation for the occurrence of Alzheimer's disease-like pathology in Down syndrome. Isolation and characterization of the gene at this locus may yield new insights into the nature of the defect causing familial Alzheimer's disease and possibly, into the etiology of all forms of Alzheimer's disease.

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No difference in HLA-A, B or DR gene frequencies could be observed between 172 control subjects and 180 HIV-1-seropositive subjects of European ancestry diagnosed through the systematic screening of blood donations. In contrast, progression to acquired immune deficiency syndrome (AIDS; 21 patients) or CD4 lymphocyte loss equal or more than 20% over a 6-month period (37 subjects) was found to be associated with the B8DR3 haplotype (relative risk = 10.64, p < 0.003, and 2.23, p < 0.092, respectively). Other independently significant associations assessed through the multivariate Cox proportional-hazards model were B16, BW21 and B35 alleles as factors of bad prognosis. Conversely, A1 and DR4 alleles were factors favouring longer survival.

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