Ricardo M. Cerda-Flores

Pre-Hispanic Mesoamerican Demography Approximates the Present-Day Ancestry of Mestizos Throughout the Territory of Mexico

Over the last 500 years, admixture among Amerindians, Europeans, and Africans, principally, has come to shape the present-day gene pool of Mexicans, particularly Mestizos, who represent about 93% of the total Mexican population. In this work, we analyze the genetic data of 13 combined DNA index system-short tandem repeats (CODIS-STRs) in 1,984 unrelated Mestizos representing 10 population samples from different regions of Mexico, namely North, West, Central, and Southeast. The analysis of molecular variance (AMOVA) test demonstrated low but significant differentiation among Mestizos from different regions (F(ST) = 0.34%; P = 0.0000). Although the spatial analysis of molecular variance (SAMOVA) predicted clustering Mestizo populations into four well-delimited groups, the main differentiation was observed between Northwest when compared with Central and Southeast regions. In addition, we included analysis of individuals of Amerindian (Purepechas), European (Huelva, Spain), and African (Fang) origin. Thus, STRUCTURE analysis was performed identifying three well-differentiated ancestral populations (k = 3). STRUCTURE results and admixture estimations by means of LEADMIX software in Mestizo populations demonstrated genetic heterogeneity or asymmetric admixture throughout Mexico, displaying an increasing North-to-South gradient of Amerindian ancestry, and vice versa regarding the European component. Interestingly, this distribution of Amerindian ancestry roughly reflects pre-Hispanic Native-population density, particularly toward the Mesoamerican area. The forensic, epidemiological, and evolutionary implications of these findings are discussed herein.

Estimation of nonpaternity in the Mexican population of Nuevo Leon: a validation study with blood group markers.

A method for estimating the general rate of nonpaternity in a population was validated using phenotype data on seven blood groups (A1A2BO, MNSs, Rh, Duffy, Lutheran, Kidd, and P) on 396 mother, child, and legal father trios from Nuevo León, Mexico. In all, 32 legal fathers were excluded as the possible father based on genetic exclusions at one or more loci (combined average exclusion probability of 0.694 for specific mother-child phenotype pairs). The maximum likelihood estimate of the general nonpaternity rate in the population was 0.118 +/- 0.020. The nonpaternity rates in Nuevo León were also seen to be inversely related with the socioeconomic status of the families, i.e., the highest in the low and the lowest in the high socioeconomic class. We further argue that with the moderately low (69.4%) power of exclusion for these seven blood group systems, the traditional critical values of paternity index (PI > or = 19) were not good indicators of true paternity, since a considerable fraction (307/364) of nonexcluded legal fathers had a paternity index below 19 based on the seven markers. Implications of these results in the context of genetic-epidemiological studies as well as for detection of true fathers for child-support adjudications are discussed, implying the need to employ a battery of genetic markers (possibly DNA-based tests) that yield a higher power of exclusion. We conclude that even though DNA markers are more informative, the probabilistic approach developed here would still be needed to estimate the true rate of nonpaternity in a population or to evaluate the precision of detecting true fathers.

Micronuclei in cervical smears and peripheral blood lymphocytes from women with and without cervical uterine cancer

Cervical cancer represents the second most common malignant neoplasia in women world-wide. In Mexico, cervical cancer is the most common female malignancy. It has been recently seen an increased frequencies of micronuclei (MN) lymphocytes and cervical epithelial cells of cervical cancer patients. The aim of this hospital-based unmatched case-control study was to investigate the association between progressive stages in development of cervical cancer and frequency of micronucleated cells in the cervical epithelium and peripheral lymphocytes of 40 women, grouped by disease stage. Women at the Obstetrics and Gynecology Hospital of the Instituto Mexicano del Seguro Social (IMSS) in Monterrey, Mexico were diagnosed and classified on the bases of the Papanicolaou (PAP) smear and colposcopy/biopsy into control, low-grade squamous intraepithelial lesions (LGSIL), high-grade squamous intraepithelial lesions (HGSIL), and invasive groups. Analysis of the MN data in both cell types revealed (a) homogeneity among women within each of the four groups with regard to MN frequency, (b) in general, a correlation between MN frequency and grade of cervical lesion, and (c) a positive linear trend between the MN frequency and increased cervical cancer risk. In conclusion, we suggest that MN are a useful biomarker of cancer risk. Nonetheless, these results should be validated by other researchers.

Heritability and genetic correlations of metabolic disease-related phenotypes in Mexico: Preliminary report from the GEMM family study

ABSTRACT Cardiovascular disease (CVD) is a major cause of mortality in the Republic of Mexico, and metabolic syndrome, a complex of CVD risk factors, is increasingly prevalent. To date, however, there have been few studies of the genetic epidemiology of metabolic syndrome in Mexico. As a first step in implementing the GEMM Family Study, a large, multicenter collaborative study, we recruited 375 individuals in 21 extended families, without ascertainment on disease, at 9 medical institutions across Mexico. Participants were measured for anthropometric (stature, weight, waist circumference) and hemodynamic (blood pressure, heart rate) phenotypes; glucose, cholesterol, and triglyceride levels were measured in fasting blood. Variance components–based quantitative genetic analyses were performed using SOLAR. All phenotypes except diastolic blood pressure were significantly heritable. Consistent with the definition of metabolic syndrome, many phenotypes exhibited significant environmental correlation, and significant genetic correlations were found between measures of adiposity and fasting glucose and fasting triglyceride levels. These preliminary data represent the first heritability estimates for many of these phenotypes in the Republic of Mexico and indicate that this study design offers excellent power for future gene discovery relative to metabolic disease.

Clinical follow up of Mexican women with early onset of breast cancer and mutations in the BRCA1 and BRCA2 genes

OBJECTIVEnThis study describes the presence of mutations in BRCA1 and BRCA2 genes in a group of Mexican women and the clinical evolution of early onset breast cancer (EOBC).nnnMATERIAL AND METHODSnA prospective hospital-based study was performed in a sample of 22 women with EOBC (7 in clinical stage IIA, 8 in IIB, and 7 in IIIA). The patients attended a tertiary care hospital in northeastern Mexico in 1997 and were followed up over a 5-year period. Molecular analysis included: 1) a mutation screening by heteroduplex analysis (HA) of BRCA1 and BRCA2 genes and 2) a sequence analysis.nnnRESULTSnOf 22 patients, 14 (63.6%) showed a variant band detected by heteroduplex analysis of the BRCA1 and BRCA2 genes: 8 polymorphisms, 4 mutations of uncertain significance, and 2 novel truncated protein mutations, one in BRCAI (exon 11, 3587delT) and the other in the BRCA2 gene (exon 11, 2664InsA).nnnCONCLUSIONSnThese findings support future studies to determine the significance and impact of the genetic factor in this Mexican women population.

Chromosomal abnormalities and polymorphic variants in couples with repeated miscarriage in Mexico

Cytogenetic studies have an important role in the evaluation of couples with repeated miscarriages and poor obstetric history. To estimate the prevalence of chromosomal abnormalities and polymorphic variants in 158 couples with repeated miscarriages, a cross-sectional study was conducted in Monterrey, Mexico from 1995 to 2003. Peripheral blood lymphocytes were cultured for chromosomal studies using standard methods. Twelve couples showed chromosomal abnormalities (7.60%), two Robertsonian translocations (1.27%), two balanced translocations (1.27%), one inversion (0.63%), and one a novel insertion (0.63%). This insertion [46, XX, ins (15;8) (q26;p11p23)] is unique, and is the third reported in association with repeated abortion. Mosaicism was observed in six couples (3.80%, three with structural abnormalities and three with numerical abnormalities). A female to male ratio of 1.4:1 was observed. In addition to these chromosomal abnormalities, polymorphic variants in constitutive heterochromatin of the 1qh+, 9qh+, and 16qh+ chromosomes were observed in 25 couples (15.82%), of the Yqh+ chromosome in 21 couples (13.29%), and of satellite in 35 couples (22.15%). In conclusion, chromosome analysis is necessary for appropriate clinical management of these patients.

Sister chromatid exchanges in peripheral lymphocytes from women with carcinoma of the uterine cervix

Sister chromatid exchanges (SCE) are reciprocal exchanges between sister chromatids. It has been reported that in patients with cervical cancer, the frequency of SCE in peripheral lymphocytes is significantly higher than that in normal individuals; however, other studies have shown no significant difference. The aim of this unmatched case-control study was to compare the mean number of SCE per metaphase in lymphocytes from women with and without carcinoma of the cervix uteri. The SCE specimens were prepared by the fluorescence plus giemsa technique in peripheral lymphocytes from 28 women with carcinoma of cervix uteri and 28 controls. The mean number of SCE per metaphase in women with carcinoma of cervix uteri (7.80 +/- 1.05) was higher than the control group (6.98 +/- 1.13) (P < 0.05; t-test). This study had a statistical power of 0.80 and an alpha value of 0.05. This finding suggests that an increased number of SCE in peripheral lymphocytes is associated with cervical cancer. We consider that the lack of reported association of SCE and cervical cancer might be attributed to the none determination of the statistical power and sample size.

Human leukocyte antigens I and II haplotypes associated with human papillomavirus 16-positive invasive cervical cancer in Mexican women.

Infection with human papillomavirus (HPV), mainly HPV type 16, is the major etiologic factor associated with cervical cancer (CC), but HPV infection alone is not sufficient for progression of precursor lesions. Host genetic susceptibility may lead to abnormal immune response resulting from virus persistence. Several studies have suggested a possible association with specific human leukocyte antigen (HLA) class I and II alleles and CC, but results are not consistent. The association of genetic HLA class I (A and B) and HLA class II (DR*B1 and DQ*B1) haplotypes with HPV16-positive CC (n = 104) and base population controls (n = 104) was evaluated in this Mexican population study. Sequence-specific primer HLA genes were determined by polymerase chain reaction (PCR)-based methods in peripheral blood cell counts (PCR sequence-specific oligonucleotides). The cervical swabs of 208 women were tested for HPV16 by Hybrid Capture II. Allele and haplotype HLA frequencies, Hardy-Weinberg tests, and a haplotype homogeneity test were estimated using the Arlequin software v. 3.01. Odds ratio (OR) was calculated to compare cases and control women. Consistent associations across other studies in women with CC and infected by HPV16 were observed for HLA-DRB1*15 (OR, 3.9; 95% CI, 1.6-10.2) and the haplotype DRB1*15 DQB1*0602 (OR, 4.1; 95% CI, 1.4-12.7) compared with control women. The HLA-A2-B44-DR4-DQ*0302, HLA-A24-B35-DR16-DQ*0301, and HLA-A2-B40-DR4-DQ*0302 haplotypes showed a positive association with CC (OR, >1), whereas HLA-A2-B39-DR4-DQ*0302, HLA-A24-B35-DR4-DQ*0302, and HLA-A68-B40-DR4-DQ*0302 showed a negative association (OR, <1). These results support the hypothesis that some HLA class I and II haplotypes could be involved with susceptibility for developing CC. Abbreviations: Cervical Cancer-CC, confidence interval-CI, human leukocyte antigens-HLA, human papillomavirus-HPV, odds ratio-OR, polymerase chain reaction-PCR, relative risk-RR, relative light units-RLU, ribonucleic acid-RNA, sequence-sensitive oligonucleotide-SSO

DNA damage evaluated by comet assay in Mexican patients with type 2 diabetes mellitus

We conducted a case–control study to assess whether general DNA damage levels evaluated by comet assay (length of tail comet, tail extent moment, and olive tail moment) differ in Mexican patients with type 2 diabetes mellitus (DM2). The sample included 71 Mexican patients with DM2 who had developed the disease >5xa0years previously and had been treated with oral hypoglycemic drugs (sulfonylurea and/or metformin), with no microvascular or macrovascular complications. These patients were classified into three groups according to age: (I) 40–50xa0years, (II) 51–60xa0years, and (III) 61–70xa0years. A control group of 14 individuals (40–50xa0years) without DM2 was included. Our results showed there was a slight but not significant increase in DNA damage in the two groups of patients with DM2 aged between 40 and 60xa0years compared with the 61–70-year-old patient group and controls. In conclusion, given that general DNA damage was similar in the three groups of patients with DM2 and the control group, it is possible that these cells showed similar oxidative damage, as has been proposed previously.

Prevalence of NIDDM in Mexicans with paraphyletic and polyphyletic surnames.

It has been hypothesized that the greater prevalence of non‐insulin‐dependent diabetes mellitus (NIDDM) in Mexicans may be related to their greater degree of Amerindian genetic admixture (AGA). The aim of this unmatched case–control study was to correlate the prevalence of NIDDM with AGA in 10 Mexican Mestizo populations non‐randomly selected by surname. A sample of 1,699 unrelated persons, >44 years and residing in the state of Nuevo León, was selected on the basis of paraphyletic or polyphyletic surnames and interviewed in the Instituto Mexicano del Seguro Social (IMSS). All subjects received a medical examination, and diabetes was diagnosed on the basis of World Health Organization criteria. Three genetic marker systems were analyzed, and the percentage of AGA was calculated. Logistic regression analysis was performed with the prevalence as the dependent variable and sex and surname as the independent variables. The Spearman rank–order correlation analysis was calculated between the age‐adjusted prevalence (45–75+ years) and AGA. The correlation revealed a pattern of increasing prevalence of NIDDM with increasing Amerindian ancestry by surname. Am. J. Hum. Biol. 12:721–728, 2000.