Ricardo Gamboa

DNA sequencing of HLA-B alleles in Mexican patients with Takayasu arteritis

Takayasu arteritis (TA) is characterized by a pulseless condition and occurs frequently in young females from Asian and South American countries. It has been associated with Mayor Histocompatibility Complex (MHC) genes in different populations. Recent data indicate direct participation of HLA-B alleles in the susceptibility to the disease. This fact was explored in an associative study with TA to establish if some region in the exon 2, intron 2 or in the exon 3 of HLA-B alleles is common in the alleles associated with TA and at the same time to know if a specific sequence or an epitope, more than an allele, would be responsible for the susceptibility to this vasculitis. We studied HLA-B alleles of 12 Mexican patients with TA using PCR-SSP and sequencing. The analysis by PCR-SSP in 12 patients showed that five of them showed the B*15 allele, three the B*40 allele and two the B*39 allele, the remaining two presented the B*44 allele. Sequence analysis enabled us to define that the B*39 subtypes are B*3908; B*15 subtypes are B*1510, B*1515, B*1522 and B*1531; and the B*40 subtypes are B*4005 and B*4008. An individual with B*51 (B*5107) and another with B*52 (B*5201) alleles were also identified. The sequences of the intron 2 seem be heterogeneous. Analysis at the 63 and 67 positions of HLA-B alleles showed that 9 of them have similarity in some of these positions with the residues detected in the B*5201 and B*3902 alleles associated with TA in Asian populations. The results indicate that there is heterogeneity in the alleles associated with TA in Mexicans but, in spite of that heterogeneity, the alleles associates can be separated into three groups: B*39, B*15 and B*40, whose subtypes are rare and apparently of recent generation in Mexico, probably by recombination events at intron 2 level. The sequences analysis also shows that most of the alleles detected in the Mexican patients share two epitopes described in the susceptibility alleles in Asian populations, suggesting that these epitopes could be responsible for the susceptibility to develop the disease in spite of the allele in which are found.

HLA-DR4 allele frequencies on Indian and Mestizo population from Mexico

Using PCR-SSOP and sequencing, we examined DRB1*04 nucleotide polymorphism in 137 DR4-positive Mexican healthy individuals (46 Mexican Mestizos, 64 Mazatecans, and 27 Nahuas), carrying a total of 147 DR4 haplotypes. Eleven different DRB1*04 alleles were detected in Mexican Mestizo population, whereas, in the two Indian groups a restricted polymorphism was observed (5 variants in Mazatecans and 4 in Nahuas). DRB1*0407 was the most frequent allele (gf = 0.106 in Mexican Mestizos, gf = 0.281 in Mazatecans, and gf = 0.189 in Nahuas). In spite of the restriction in polymorphism, there were differences on DRB1*04 alleles found in Mexicans mainly between Mazatecan and Nahua populations. DRB1*0403 was characteristic allele in Nahua ethnic group, whereas, 0404 and 0411 were predominant alleles in Mazatecans. This data corroborates the restricted polymorphism of DRB1*04 alleles in American populations. In spite of the restriction in this polymorphism, differences in frequencies of DRB1*04 alleles could help distinguish each population.

Influence of the Apolipoprotein E Polymorphism on Plasma Lipoproteins in a Mexican Population

Abstract The influence of apolipoprotein E (APOE) genotypes on plasma lipid levels was determined in 278 Mexican individuals. The most frequent genotype was E3/3 (80.5%) followed by E3/4 (12.5%), E2/3 (5.0%), E2/4 (1.4%), and E4/4 (0.3%). Our data are similar to those previously described for Mexican-American and American Indian populations, which show the highest frequency worldwide of the APOE*3 and the E3/3 genotype. Compared to female carriers of the E3/3 genotype, women with the E3/4 genotype presented increased low-density lipoprotein cholesterol (117 ± 28.0 mg/dL vs. 134.0 ± 31.7 mg/dL, p < 0.05), and total cholesterol (179.4 ± 33.4 mg/dL vs. 197.5 ± 35.4 mg/dL, p < 0.01). Also, we detected increased high-density lipoprotein concentrations in women with the E2/3 genotype (53.7 ± 19.5 mg/dL) when compared to women with the E3/3 genotype (45.2 ± 12.0 mg/dL) (p < 0.032). Our data suggest that genetic variation at the APOE locus in the Mexican population is a genetic factor that influences plasma lipid levels. This effect was observed only in the female population. Additional studies attempting to correlate APOE polymorphism with plasma lipid profile in a large number of individuals would be helpful in establishing the true significance of this polymorphism in the Mexican population.

HLA-DRB and HLA-DQB loci in the genetic susceptibility to develop glaucoma in Mexicans.

PURPOSEnGlaucoma is a clinically heterogeneous disease with a pathophysiology that may include genetic susceptibility, possibly associated with an immunologic disorder. The aim of this study was to determine whether the DNA polymorphisms located in the HLA-DRB1 and HLA-DQB1 genes show a specific association pattern in Mexican mestizo patients with primary open-angle glaucoma.nnnMETHODSnThis was a cross-sectional, case-control, multicenter study. We analyzed the HLA-DRB1 and DQB1 loci of 81 Mexican mestizo nonrelated patients with primary open-angle glaucoma and 98 healthy ethnic matched control subjects. Patients were diagnosed clinically and by visual fields examination. HLA typing was performed by PCR-SSO reverse dot blot.nnnRESULTSnWe documented increased frequencies of HLA-DRB1*0301, DRB1*1101, DRB1*0701, DRB1*1402, DQB1*0302, and DQB1*0301; however, none of them were significantly different from normal control subjects. Haplotype analysis showed that the HLA-DRB1*0407-DQB1*0302 haplotype is significantly increased in patients compared with control subjects (P = .0001).nnnCONCLUSIONSnThe haplotype HLA-DRB1*0407-DQB1*0302 is common among Mexican mestizo (haplotype frequency = 0.102), and it was increased in our patients (haplotype frequency = 0.259, P = .0001). This may reflect an independent association of this haplotype with the disease as the result of linkage disequilibrium or the influence of a neighboring gene. The pathophysiology of this illness is uncertain, and further studies are needed regarding the genetic susceptibility to develop primary open-angle glaucoma.

Polymorphism and distribution of HLA-DR2 alleles in Mexican populations.

DRB1*15/16 nucleotide polymorphism was analyzed in 68 DR2 positive individuals (18 Mexican Mestizos, 30 Mazatecans and 20 Nahuas), carrying a total of 75 DR2 haplotypes. HLA-DR2 was one of the most frequent specificities detected in Mazatecans and Nahuas with gene frequency (gf) of 0.232 and 0.141, respectively. In these populations DRB1*16 was the most frequent DR2 split (gf = 0.183 in Mazatecans and gf = 0.135 in Nahuas), whereas in Mexican Mestizos the most frequent was DRB1*15 (gf = 0.065). Four DRB1-DQB1 combinations in Mexican Mestizos, two in Mazatecans and one in Nahuas were in linkage disequilibrium. In spite of the restricted polymorphism, there were differences on DRB1*15/16 alleles found in Mexicans. DRB1*1501 a Caucasian allele was predominant in Mexican Mestizos, whereas DRB1*1602 an Amerindian allele was characteristic on Indian populations. An important difference was detected among the Amerindian populations studied since DRB1*1502 was only present in Mazatecans. This data corroborates the restricted polymorphism of DRB1*15/16 and the high frequency of DRB1*16 subtype in autochthonous American populations and suggest that the differences in gene frequencies of DRB1*15/16 alleles could be helpful in distinguishing each of these population.