RÉSUMÉ
Population-based identity by descent (IBD) mapping is a statistical method for detection of genetic loci that share an ancestral segment among "unrelated" pairs of individuals for a disease. As a complementary method to genome-wide association studies, IBD mapping is robust to allelic heterogeneity and may identify rare inherited variants when combined with sequence data. Our objective is to identify the causal genes for diastolic blood pressure (DBP). We applied a population-based IBD mapping method to 105 unrelated individuals selected from the family data provided for the Genetic Analysis Workshop 19. Using the genome-wide association study data (ie, the microarray data), chromosome 3 was scanned for IBD sharing segments among all pairs of these individuals. At the chromosomal region with the most significant relationship between IBD sharing and DBP, the whole genome sequence data were examined to identify the risk variants for DBP. The most significant chromosomal region that was identified to have a relationship between the IBD sharing and DBP was at 3q12.3 (p = 0.0016), although it did not achieve the chromosome-wide significance level (p = 0.00012). This chromosomal region contains 1 gene, ZPLD1, which has been reported to be associated with cerebral cavernous malformations, a disease with enlarged small blood vessels (capillaries) in the brain. Although 24 deleterious variants were identified at this region, no significant association was found between these variants and DBP (p = 0.40). We presented a mapping strategy which combined a population-based IBD mapping method with sequence data analyses. One gene was located at a chromosomal region identified by this method for DBP. However, further study with a large sample size is needed to assess this result.
RÉSUMÉ
Systemic lupus erythematosus (SLE) is an autoimmune disease in which polymorphisms within the human leukocyte antigen (HLA) region have been associated to its etiology. For this study, HLA-DQB1, DQA1, and DRB1 genes were typed by polymerase chain reaction-sequence-specific primer in 237 individuals, taken from 74 families, who had a member with SLE, and who had their residence in the western region of Mexico; as well as in 159 ethnically matched healthy volunteers taken from 32 families. Genotype and allele frequency analysis was performed in 74 SLE patients and 54 unrelated controls. Precise three-loci identification of independent haplotypes was performed in 48 patients and 54 controls by familial segregation. Genotype distribution at each loci was concordant with Hardy-Weinberg's equilibrium in the control group. In general, no genotype effect was observed in SLE patients. Allele distribution comparison showed in the SLE group a significant increase of HLA-DQA1*0102, DQB1*0402, and DRB1*15; whereas alleles HLA-DQB1*0303 and *0501 were significantly decreased. SLE patients showed haplotype DQB1*0602-DQA1-*0102-DRB1*15 increased. As expected, patients with SLE have a reduced haplotype genetic diversity. The associations found in this study are related to an ancestral haplotype that has been observed in SLE populations of different origins.