Origins of U.S. Hispanics. Implications for diabetes

The role of health system penetration rate in estimating the prevalence of type 1 diabetes in children and adolescents using electronic health records

OBJECTIVE

Having sufficient population coverage from the electronic health records (EHRs)-connected health system is essential for building a comprehensive EHR-based diabetes surveillance system. This study aimed to establish an EHR-based type 1 diabetes (T1D) surveillance system for children and adolescents across racial and ethnic groups by identifying the minimum population coverage from EHR-connected health systems to accurately estimate T1D prevalence.

MATERIALS AND METHODS

We conducted a retrospective, cross-sectional analysis involving children and adolescents <20 years old identified from the OneFlorida+ Clinical Research Network (2018-2020). T1D cases were identified using a previously validated computable phenotyping algorithm. The T1D prevalence for each ZIP Code Tabulation Area (ZCTA, 5 digits), defined as the number of T1D cases divided by the total number of residents in the corresponding ZCTA, was calculated. Population coverage for each ZCTA was measured using observed health system penetration rates (HSPR), which was calculated as the ratio of residents in the corresponding ZTCA and captured by OneFlorida+ to the overall population in the same ZCTA reported by the Census. We used a recursive partitioning algorithm to identify the minimum required observed HSPR to estimate T1D prevalence and compare our estimate with the reported T1D prevalence from the SEARCH study.

RESULTS

Observed HSPRs of 55%, 55%, and 60% were identified as the minimum thresholds for the non-Hispanic White, non-Hispanic Black, and Hispanic populations. The estimated T1D prevalence for non-Hispanic White and non-Hispanic Black were 2.87 and 2.29 per 1000 youth, which are comparable to the reference study's estimation. The estimated prevalence of T1D for Hispanics (2.76 per 1000 youth) was higher than the reference study's estimation (1.48-1.64 per 1000 youth). The standardized T1D prevalence in the overall Florida population was 2.81 per 1000 youth in 2019.

CONCLUSION

Our study provides a method to estimate T1D prevalence in children and adolescents using EHRs and reports the estimated HSPRs and prevalence of T1D for different race and ethnicity groups to facilitate EHR-based diabetes surveillance.

Parsing the Paradox: Hispanic Mortality in the US by Detailed Cause of Death

US Hispanics are a disadvantaged population that paradoxically has lower mortality rates than non-Hispanic whites. We conducted a descriptive analysis of age-adjusted mortality rates for 113 causes of death for US Hispanics (USH) and US non-Hispanic whites (USNHW) during 1999-2015. All-cause, age-adjusted mortality rates per 100,000 were: 581.1 USH and 788.8 USNHW. Lower Hispanic mortality from cancer, heart disease, and respiratory disease accounted for almost all the all-cause mortality gap. USH rates were higher than USNHW rates for cancers of the stomach, liver, and cervix; diabetes mellitus; liver disease; and homicide. Behavioural factors such as less smoking among USH probably drive their lower rates for the major chronic diseases. Social disadvantages contribute to elevated risk for certain cancers, diabetes, and homicide. Efforts to improve Hispanic well-being in the US should remedy the social disadvantages while preserving the health advantages the population enjoys.

Identification of novel common breast cancer risk variants at the 6q25 locus among Latinas

Background

Breast cancer is a partially heritable trait and genome-wide association studies (GWAS) have identified over 180 common genetic variants associated with breast cancer. We have previously performed breast cancer GWAS in Latinas and identified a strongly protective single nucleotide polymorphism (SNP) at 6q25, with the protective minor allele originating from indigenous American ancestry. Here we report on fine mapping of the 6q25 locus in an expanded sample of Latinas.

Methods

We performed GWAS in 2385 cases and 6416 controls who were either US Latinas or Mexican women. We replicated the top SNPs in 2412 cases and 1620 controls of US Latina, Mexican, and Colombian women. In addition, we validated the top novel variants in studies of African, Asian and European ancestry. In each dataset we used logistic regression models to test the association between SNPs and breast cancer risk and corrected for genetic ancestry using either principal components or genetic ancestry inferred from ancestry informative markers using a model-based approach.

Results

We identified a novel set of SNPs at the 6q25 locus associated with genome-wide levels of significance (p = 3.3 × 10^− 8 - 6.0 × 10^− 9) not in linkage disequilibrium (LD) with variants previously reported at this locus. These SNPs were in high LD (r² > 0.9) with each other, with the top SNP, rs3778609, associated with breast cancer with an odds ratio (OR) and 95% confidence interval (95% CI) of 0.76 (0.70–0.84). In a replication in women of Latin American origin, we also observed a consistent effect (OR 0.88; 95% CI 0.78–0.99; p = 0.037). We also performed a meta-analysis of these SNPs in East Asians, African ancestry and European ancestry populations and also observed a consistent effect (rs3778609, OR 0.95; 95% CI 0.91–0.97; p = 0.0017).

Conclusion

Our study adds to evidence about the importance of the 6q25 locus for breast cancer susceptibility. Our finding also highlights the utility of performing additional searches for genetic variants for breast cancer in non-European populations.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1085-9) contains supplementary material, which is available to authorized users.

Genetic associations with lipoprotein subfraction measures differ by ethnicity in the multi-ethnic study of atherosclerosis (MESA)

A recent genome-wide association study associated 62 single nucleotide polymorphisms (SNPs) from 43 genomic loci, with fasting lipoprotein subfractions in European–Americans (EAs) at genome-wide levels of significance across three independent samples. Whether these associations are consistent across ethnicities with a non-European ancestry is unknown. We analyzed 15 lipoprotein subfraction measures, on 1677 African–Americans (AAs), 1450 Hispanic–Americans (HAs), and 775 Chinese–Americans (CHN) participating in the multi-ethnic study of atherosclerosis (MESA). Genome-wide data were obtained using the Affymetrix 6.0 and Illumina HumanOmni chips. Linear regression models between genetic variables and lipoprotein subfractions were adjusted for age, gender, body mass index, smoking, study center, and genetic ancestry (based on principal components), and additionally adjusted for Mexican/Non-Mexican status in HAs. A false discovery rate correction was applied separately within the results for each ethnicity to correct for multiple testing. Power calculations revealed that we did not have the power for SNP-based measures of association, so we analyzed phenotype-specific genetic risk scores (GRSs), constructed as in the original genome-wide analysis. We successfully replicated all 15 GRS–lipoprotein associations in 2527 EAs. Among the 15 significant GRS–lipoprotein associations in EAs, 11 were significant in AAs, 13 in HAs, and 1 in CHNs. Further analyses revealed that ethnicity differences could not be explained by differences in linkage disequilibrium, lipid lowering drugs, diabetes, or gender. Our study emphasizes the importance of ethnicity (here indexing genetic ancestry) in genetic risk for CVD and highlights the need to identify ethnicity-specific genetic variants associated with CVD risk.

Identification of a novel locus associated with skin colour in African-admixed populations

Skin pigmentation is a complex trait that varies largely among populations. Most genome-wide association studies of this trait have been performed in Europeans and Asians. We aimed to uncover genes influencing skin colour in African-admixed individuals. We performed a genome-wide association study of melanin levels in 285 Hispanic/Latino individuals from Puerto Rico, analyzing 14 million genetic variants. A total of 82 variants with p-value ≤1 × 10⁻⁵ were followed up in 373 African Americans. Fourteen single nucleotide polymorphisms were replicated, of which nine were associated with skin colour at genome-wide significance in a meta-analysis across the two studies. These results validated the association of two previously known skin pigmentation genes, SLC24A5 (minimum p = 2.62 × 10⁻¹⁴, rs1426654) and SLC45A2 (minimum p = 9.71 × 10⁻¹⁰, rs16891982), and revealed the intergenic region of BEND7 and PRPF18 as a novel locus associated with this trait (minimum p = 4.58 × 10⁻⁹, rs6602666). The most significant variant within this region is common among African-descent populations but not among Europeans or Native Americans. Our findings support the advantages of analyzing African-admixed populations to discover new genes influencing skin pigmentation.

Racial Differences in Food Allergy Phenotype and Health Care Utilization among US Children

BACKGROUND

Food allergy (FA) is a prevalent condition in the United States, but little is known about its phenotypes in racial minority groups.

OBJECTIVE

The objective of this study was to characterize disease phenotypes and disparities in health care utilization among African American (AA), Hispanic, and white children with FA.

METHODS

We conducted a large, 2-center, retrospective cohort study of children aged 0-17 years with FA seen in allergy/immunology clinics at 2 urban tertiary care centers in the United States. We used multiple logistic regression analyses adjusted for age, gender, and insurance.

RESULTS

The cohort of 817 children was composed of 35% AA, 12% Hispanic, and 53% non-Hispanic white. Compared with non-Hispanic white children, AA children had significantly higher odds of having asthma and eczema (P < .01), and significantly higher odds of allergy to wheat, soy, corn, fish, and shellfish (P < .01). Compared with non-Hispanic white children, Hispanic children had significantly higher odds of allergy to corn, fish, and shellfish (P < .01), and higher odds of eczema (P < .01), but a similar rate of asthma (P = .44). In this cohort, 55%, 18%, and 11% of AA, Hispanic, and white children were covered by Medicaid, respectively (P < .00001). Compared with whites, AA and Hispanic children had a shorter duration of follow-up for FA with an allergy specialist and higher rates of FA-related anaphylaxis and emergency department visits (P < .01).

CONCLUSIONS

FA phenotypes and health care utilization differ among children of different racial and/or ethnic backgrounds in the United States that put AA and Hispanic children at higher risks of adverse outcome than white children. These differences include coexistent atopic conditions, less well recognized food allergens, and higher rates of anaphylaxis.

Culturally Competent Interventions for Hispanic Adults With Type 2 Diabetes

Culturally competent interventions have been developed to improve outcomes for Hispanic adults with type 2 diabetes. The purpose of this systematic review is to synthesize the research on culturally competent interventions for this vulnerable population. A systematic approach was used to locate empirical reports (n = 11). Interventions were multifaceted with the majority demonstrating significant improvements in clinical outcomes, behavioral outcomes, and diabetes-related knowledge. Culturally competent interventions have the potential to improve outcomes in Hispanic adults with type 2 diabetes. However, improvements were modest and attrition was moderate to high in many studies. Addressing linguistic and cultural barriers to care are important beginnings to improving health outcomes for Hispanic adults with type 2 diabetes.

The Association between HMGA1 rs146052672 Variant and Type 2 Diabetes: A Transethnic Meta-Analysis

The high-mobility group A1 (HMGA1) gene has been previously identified as a potential novel candidate gene for susceptibility to insulin resistance and type 2 diabetes (T2D) mellitus. For this reason, several studies have been conducted in recent years examining the association of the HMGA1 gene variant rs146052672 (also designated IVS5-13insC) with T2D. Because of non-univocal data and non-overlapping results among laboratories, we conducted the current meta-analysis with the aim to yield a more precise and reliable conclusion for this association. Using predetermined inclusion criteria, MEDLINE, PubMed, Web of Science, Scopus, Google Scholar and Embase were searched for all relevant available literature published until November 2014. Two of the authors independently evaluated the quality of the included studies and extracted the data. Values from the single studies were combined to determine the meta-analysis pooled estimates. Heterogeneity and publication bias were also examined. Among the articles reviewed, five studies (for a total of 13,789 cases and 13,460 controls) met the predetermined criteria for inclusion in this meta-analysis. The combined adjusted odds ratio estimates revealed that the rs146052672 variant genotype had an overall statistically significant effect on increasing the risk of development of T2D. As most of the study subjects were Caucasian, further studies are needed to establish whether the association of this variant with an increased risk of T2D is generalizable to other populations. Also, in the light of this result, it would appear to be highly desirable that further in-depth investigations should be undertaken to elucidate the biological significance of the HMGA1 rs146052672 variant.

Diabetes in the Hispanic population

As the Hispanic population in the United States increases, more primary care physicians are being challenged to address the high incidence of diabetes and related metabolic disorders in Hispanic American patients. A variety of genetic, environmental, and socioeconomic factors contribute to this group's high susceptibility to diabetes. In this article, Drs Idrogo and Mazze discuss diagnosis of diabetes in Hispanic patients, as well as culturally sensitive screening and treatment strategies.

Clinical outcomes and genome-wide association for a brain methylation site in an antidepressant pharmacogenetics study in Mexican Americans

OBJECTIVE

The authors compared the effectiveness of fluoxetine and desipramine treatment in a prospective double-blind pharmacogenetics study in first-generation Mexican Americans and examined the role of whole-exome functional gene variations in the patients' antidepressant response.

METHOD

A total of 232 Mexican Americans who met DSM-IV criteria for major depressive disorder were randomly assigned to receive 8 weeks of double-blind treatment with desipramine (50-200 mg/day) or fluoxetine (10-40 mg/day) after a 1-week placebo lead-in period. Outcome measures included the Hamilton Depression Rating Scale (HAM-D), the Hamilton Anxiety Rating Scale, and the Beck Depression Inventory. At week 8, whole-exome genotyping data were obtained for 36 participants who remitted and 29 who did not respond to treatment.

RESULTS

Compared with desipramine treatment, fluoxetine treatment was associated with a greater reduction in HAM-D score, higher response and remission rates, shorter time to response and remission, and lower incidences of anticholinergic and cardiovascular side effects. Pharmacogenetics analysis showed that exm-rs1321744 achieved exome-wide significance for treatment remission. This variant is located in a brain methylated DNA immunoprecipitation sequencing site, which suggests that it may be involved in epigenetic regulation of neuronal gene expression. This and two other common gene variants provided a highly accurate cross-validated predictive model for treatment remission of major depression (receiver operating characteristic integral=0.95).

CONCLUSIONS

Compared with desipramine, fluoxetine treatment showed a more rapid reduction of HAM-D score and a lower incidence of side effects in a population comprising primarily first-generation Mexican Americans with major depression. This study's pharmacogenetics approach strongly implicates the role of functional variants in antidepressant treatment response.

The role of local ancestry adjustment in association studies using admixed populations

Association analysis using admixed populations imposes challenges and opportunities for disease mapping. By developing some explicit results for the variance of an allele of interest conditional on either local or global ancestry and by simulation of recently admixed genomes we evaluate power and false-positive rates under a variety of scenarios concerning linkage disequilibrium (LD) and the presence of unmeasured variants. Pairwise LD patterns were compared between admixed and nonadmixed populations using the HapMap phase 3 data. Based on the above, we showed that as follows:

For causal variants with similar effect size in all populations, power is generally higher in a study using admixed population than using nonadmixed population, especially for highly differentiated SNPs. This gain of power is achieved with adjustment of global ancestry, which completely removes any cross-chromosome inflation of type I error rates, and addresses much of the intrachromosome inflation.

If reliably estimated, adjusting for local ancestry precisely recovers the localization that could have been achieved in a stratified analysis of source populations. Improved localization is most evident for highly differentiated SNPs; however, the advantage of higher power is lost on exactly the same differentiated SNPs.

In the real admixed populations such as African Americans and Latinos, the expansion of LD is not as dramatic as in our simulation.

While adjustment for global ancestry is required prior to announcing a novel association seen in an admixed population, local ancestry adjustment may best be regarded as a localization tool not strictly required for discovery purposes.

Does the "Hispanic paradox" occur in rheumatoid arthritis? Survival data from a multiethnic cohort

OBJECTIVE

Despite lower socioeconomic status (SES) and higher disease burden, Hispanics in the US paradoxically display equal or lower mortality on average than non-Hispanic whites. Our objective was to determine if the "Hispanic paradox" occurs among patients with rheumatoid arthritis (RA).

METHODS

In a cohort of 706 RA patients, we compared differences in RA severity and comorbidity between Hispanic and non-Hispanic white ethnic groups at baseline. Cox proportional hazards models were used to estimate and compare mortality risk between Hispanics and non-Hispanic whites.

RESULTS

We studied 706 patients with RA, of whom 434 were Hispanic and 272 were non-Hispanic white. Hispanics had significantly lower SES, greater inflammation, as well as higher tender and swollen joint counts. Patients were observed for 6,639 patient-years, during which time 229 deaths occurred by the censoring date (rate 3.4 per 100 person-years; 95% confidence interval 3.0, 3.9). Age- and sex-adjusted mortality was not significantly different between the 2 ethnic groups (hazard ratio [HR] 0.96). After adjustment for comorbidities, RA severity, and level of acculturation, mortality among Hispanics was lower (HR 0.56, P = 0.004).

CONCLUSION

Despite greater severity in most clinical manifestations and lower SES among Hispanics, paradoxically, their mortality was not increased. Further research is needed to understand the mechanisms underlying this survival paradox.

Hodgkin lymphoma incidence in California Hispanics: influence of nativity and tumor Epstein-Barr virus

PURPOSE

For classical Hodgkin lymphoma (HL), migrant studies could elucidate contributions of environmental factors (including Epstein-Barr virus (EBV)) to the lower rates in non-whites. Given the well-described etiologic complexity of HL, this research requires a large, immigrant population, such as California Hispanics.

METHODS

With 1988-2004 California Cancer Registry data (2,595 Hispanic, 8,637 white HL cases) and tumor cell EBV status on a subset (218 Hispanics, 656 whites), we calculated ethnicity- and nativity-specific HL incidence rates simultaneously by age, sex, and histologic subtype, and tumor cell EBV prevalence.

RESULTS

Compared with white rates, Hispanic HL rates were lower overall (70 %) and for nodular sclerosis HL, particularly among young adults (60-65 % for females). However, they were higher among children (200 %) and older adults, and for mixed cellularity HL. Compared with rates in foreign-born Hispanics, rates in US-born Hispanics were higher among young adults (>threefold in females), lower for children and adults over age 70, and consistently intermediate compared with rates in whites. EBV tumor prevalence was 67, 32, and 23 % among foreign-born Hispanics, US-born Hispanics, and whites, respectively, although with variation by age, sex, and histology.

CONCLUSIONS

Findings strongly implicate environmental influences, such as nativity-related sociodemographic differences, on HL occurrence. In addition, lower young adult rates and higher EBV prevalence in US-born Hispanics than in whites raise questions about the duration/extent of environmental change for affecting HL rates and also point to ethnic differences in genetic susceptibility. Lesser variation in mixed cellularity HL rates and greater variation in rates for females across groups suggest less modifiable factors interacting with environmental influences.

Characterization of mitochondrial haplogroups in a large population-based sample from the United States

Mitochondrial DNA (mtDNA) haplogroups are valuable for investigations in forensic science, molecular anthropology, and human genetics. In this study, we developed a custom panel of 61 mtDNA markers for high-throughput classification of European, African, and Native American/Asian mitochondrial haplogroup lineages. Using these mtDNA markers, we constructed a mitochondrial haplogroup classification tree and classified 18,832 participants from the National Health and Nutrition Examination Surveys (NHANES). To our knowledge, this is the largest study to date characterizing mitochondrial haplogroups in a population-based sample from the United States, and the first study characterizing mitochondrial haplogroup distributions in self-identified Mexican Americans separately from Hispanic Americans of other descent. We observed clear differences in the distribution of maternal genetic ancestry consistent with proposed admixture models for these subpopulations, underscoring the genetic heterogeneity of the United States Hispanic population. The mitochondrial haplogroup distributions in the other self-identified racial/ethnic groups within NHANES were largely comparable to previous studies. Mitochondrial haplogroup classification was highly concordant with self-identified race/ethnicity (SIRE) in non-Hispanic whites (94.8 %), but was considerably lower in admixed populations including non-Hispanic blacks (88.3 %), Mexican Americans (81.8 %), and other Hispanics (61.6 %), suggesting SIRE does not accurately reflect maternal genetic ancestry, particularly in populations with greater proportions of admixture. Thus, it is important to consider inconsistencies between SIRE and genetic ancestry when performing genetic association studies. The mitochondrial haplogroup data that we have generated, coupled with the epidemiologic variables in NHANES, is a valuable resource for future studies investigating the contribution of mtDNA variation to human health and disease.

A review of barriers to effective asthma management in Puerto Ricans: cultural, healthcare system and pharmacogenomic issues

BACKGROUND

Among the Hispanic community, Puerto Ricans have the highest prevalence of asthma and manifest the worst outcomes. The expected growth of the Hispanic population in the USA in the next several decades make elimination of disparate care in Puerto Rican asthmatics a matter of national importance. The purpose of this review of the literature (ROL) is to examine a variety of health system, genetic and cultural barriers in the Puerto Rican community which have created disparities in asthma care and outcomes among adult and pediatric Hispanic populations. In addition, this ROL describes several culturally sensitive, community-based educational interventions which can be used as a framework for future projects to improved asthma outcomes.

METHODS

Databases searched included Medline, PubMED, EBSCOhost, PsycINFO, CINAHL, Google Scholar and ERIC. Papers published in English from January 1990 to January 2012 were reviewed.

RESULTS

Health system policies, insurer compensation patterns, clinician attitudes and cultural values/folk remedies in the Puerto Rican community represent barriers to effective asthma management, the use of controller medication and the implementation of educational interventions. In addition, genetic factors involving the beta-2 adrenergic receptor gene, which impair the response to albuterol, appear to contribute to poorer outcomes in Puerto Rican asthmatics. In contrast, several comprehensive, community-based, culturally sensitive educational interventions such as Controlling Asthma in American Cities Project (CAACP), the Racial and Ethnic Approach to Community Health in the US Program and Healthy Hoops programs (REACH) have been described.

CONCLUSIONS

We believe that culturally sensitive community-based asthma education programs can serve as models for programs targeted toward Puerto Ricans to help decrease asthma morbidity. Moreover, greater sensitivity to Puerto Rican mores and folk remedies on the part of healthcare providers may improve the patient-clinician rapport and, hence, asthma outcomes. Finally, given ethnically based differences in pharmacogenomics, clinical trials targeting the Puerto Rican population may help to better define optimal asthma medication regimens in this ethnic group.

Analysis of Patterns of Gene Expression Variation within and between Ethnic Populations in Pediatric B-ALL

B-Precursor acute lymphoblastic leukemia (B-ALL) is the most common childhood cancer. Although 80% of B-ALL patients are able to be cured, significant challenges persist. Significant disparities in clinical outcomes and mortality rates exist between racial/ethnic populations. The objective of this study was to determine whether gene expression levels significantly differ between ethnic populations. We compared gene expression levels between four ethnic populations (Whites, Blacks, Hispanics, and Asians) in the United States. Additionally, we performed network and pathway analysis to identify gene networks and pathways. Gene expression data involved 198 samples distributed as follows: 126 Whites, 51 Hispanics, 13 Blacks, and 8 Asians. We identified 300 highly significantly (P < 0.001) differentially expressed genes between the four ethnic populations. Among the identified genes included the genes PHF6, BRD3, CRLF2, and RNF135 which have been implicated in pediatric B-ALL. We identified key pathways implicated in B-ALL including the PDGF, PI3/AKT, ERBB2-ERBB3, and IL-15 signaling pathways.

Implications in the difference of anti-Mi-2 and -p155/140 autoantibody prevalence in two dermatomyositis cohorts from Mexico City and Guadalajara

Introduction

Autoantibodies and clinical manifestations in polymyositis/dermatomyositis (PM/DM) are affected by both genetic and environmental factors. The high prevalence of DM and anti-Mi-2 in Central America is thought to be associated with the high UV index of the area. The prevalences of autoantibodies and the clinical manifestations of PM/DM were evaluated comparing two cohorts in Mexico.

Methods

Ninety-five Mexican patients with PM/DM (66 DM, 29 PM; 67 Mexico City, 28 Guadalajara) were studied. Autoantibodies were characterized by immunoprecipitation using ³⁵S-methionine labeled K562 cell extract. Clinical information was obtained from medical records.

Results

DM represented 69% of PM/DM and anti-Mi-2 was the most common autoantibody (35%), followed by anti-p155/140 (11%); however, anti-Jo-1 was only 4%. The autoantibody profile in adult-onset DM in Mexico City versus Guadalajara showed striking differences: anti-Mi-2 was 59% versus 12% (P = 0.0012) whereas anti-p155/140 was 9% versus 35% (P = 0.02), respectively. A strong association of anti-Mi-2 with DM was confirmed and when clinical features of anti-Mi-2 (+) DM (n = 30) versus anti-Mi-2 (-) DM (n = 36) were compared, the shawl sign (86% versus 64%, P < 0.05) was more common in the anti-Mi-2 (+) group (P = 0.0001). Levels of creatine phosphokinase (CPK) were higher in those who were anti-Mi-2 (+) but they responded well to therapy.

Conclusions

Anti-Mi-2 has a high prevalence in Mexican DM and is associated with the shawl sign and high CPK. The prevalence of anti-Mi-2 and anti-p155/140 was significantly different in Mexico City versus Guadalajara, which have a similar UV index. This suggests roles of factors other than UV in anti-Mi-2 antibody production.

The Effect of CYP2D6 Polymorphisms on Dextromethorphan Metabolism in Mexican Americans

CYP2D6 is one of the most polymorphic of the cytochrome P450 enzymes. Genetic differences in this enzyme have been reported in whites, blacks, and Asians. However, there is very little information about polymorphisms of this enzyme in Mexican Americans. The objectives of the present study were to assess the metabolic activity of CYP2D6 in a Mexican American population using dextromethorphan and to correlate this metabolic activity with a genotypic analysis. The sample consisted of 50 Mexican American subjects and 25 non-Mexican American controls. Overnight urine samples were collected and analyzed by high-performance liquid chromatography to calculate the metabolic ratio of dextromethorphan to dextrorphan. Blood samples were collected for genotypic analysis of CYP2D6 alleles. The frequency of the poor metabolizer phenotype was the same in the Mexican American group and the non-Mexican American group (6% vs 5.5%). The frequency of alleles in the Mexican American group was similar to frequencies published in other reports for non-Hispanic whites: *4 = 0.17, *5 = 0.02, *10 = 0.01, *17 = 0.02, *xN = 0.03. These results indicate that compared with non-Hispanic whites, Mexican Americans have a similar proportion of poor metabolizer phenotype and similar genetic polymorphisms of CYP2D6.

CYP2D6Genotype and Phenotype in Amerindians of Tepehuano Origin and Mestizos of Durango, Mexico

Although the drug-metabolizing enzyme CYP2D6 has been studied extensively in subjects of differing ethnicities, limited CYP2D6 pharmacogenetic data are available for the Amerindian population and Mestizos of Mexico. Dextromethorphan hydroxylation phenotype was studied in Tepehuano Amerindian (n = 58) and Mestizo (n = 88) subjects, and 195 individuals (85 Tepehuano Amerindians and 110 Mestizos) were genotyped by polymerase chain reaction-restriction fragment length polymorphism methods to identify the frequencies of the CYP2D6*3, *4, *6, and *10 alleles. Tepehuano Amerindian subjects lacked the poor metabolizer (PM) phenotype, whereas in Mestizos the PM phenotype frequency was 6.8%. The CYP2D6*3, *6, and *10 alleles were not found in Tepehuano Amerindians. The CYP2D6*4 allele had a low frequency (0.006) in this Amerindian group. In the Mestizo group, the CYP2D6*3, *4, and *10 alleles had frequencies of 0.009, 0.131, and 0.023, respectively. The CYP2D6*6 allele was not found in Mestizos. The genotype-phenotype association was strongly statistically significant (r(2) = .45; P = .005) in Mestizos. The Tepehuano population was found to have a low phenotypic and genotypic CYP2D6 diversity and differed from other Amerindian groups. On the other hand, the frequencies of the CYP2D6 variant alleles in Mestizos were similar to those reported for whites.

Trends in colorectal cancer among hispanics by stage and subsite location: 1989-2006

OBJECTIVES:

Hispanic colorectal cancer (CRC) rates historically have been lower than for non-Hispanic Whites in the United States and in Florida. The aim of this study is to understand CRC trends in Florida Hispanics and non-Hispanic Whites.

METHODS:

Using a cross-sectional study design, all invasive CRCs diagnosed among Florida residents between 1989 and 2006 were accessed from the Florida Cancer Data System (FCDS). These cases were analyzed by Hispanic and non-Hispanic White ethnic identification. The Hispanic Origin Identification Algorithm was applied to the FCDS data to identify Hispanic subjects. Primary cancer site and histology data were organized according to SEER (Surveillance Epidemiology and End Results) categories. Joinpoint regression was used to generate incidence trends by stage and subsite location.

RESULTS:

Rates of CRC incidence were higher for Florida Hispanics compared with non-Hispanic Whites since the mid 1990s. There was a consistent significant increase in the incidence of distant stage CRC in Hispanics (annual percent change (APC) of 1.26 and 0.90 in males and females), whereas rates in non-Hispanics decreased significantly during the same time period (APC −1.36 and −1.28, respectively). Similar trends were found in distant-stage right-sided CRC. Among right-sided CRCs, local stage incidence rate increased for both non-Hispanic Whites and Hispanics, whereas the incidence rate for regional stage decreased for both racial/ethnic groups.

CONCLUSIONS:

Trends for distant-stage CRC are increasing among Florida Hispanics. This is a particular public health concern given that CRC is a cancer for which screening modalities exist and could imply a concomitant increase in CRC-related mortality among Florida Hispanics. Lower rates of CRC screening in Hispanics are documented at the state level, relative to non-Hispanic Whites. Screening programs targeting the Florida Hispanic population are warranted.

Improving treatment in Hispanic/Latino patients

The prevalence of type 2 diabetes mellitus is higher in Hispanic/Latino individuals living in the United States compared with their non-Hispanic white counterparts. Many factors contribute to the increased prevalence of type 2 diabetes, including biological characteristics, socioeconomic conditions, and cultural aspects. The contribution of genetics to the risk of type 2 diabetes in Hispanic/Latino patients is becoming increasingly clear, but this inherent risk factor cannot be modified. However, certain socioeconomic and cultural factors, such as reduced access to healthcare, language barriers, cultural beliefs, and lack of cultural competence by the healthcare provider, are modifiable and should be overcome in order to improve the management of type 2 diabetes in Hispanic/Latino patients. At the healthcare system level, policies should be put into place to reduce disparities between Hispanics/Latinos and non-Hispanic whites regarding health insurance coverage and access to healthcare. At the healthcare provider and patient level, cultural beliefs should be taken into consideration when selecting adequate treatment. Overall, type 2 diabetes management should be individualized by identifying the preferred language and level of acculturation for each patient. These considerations are necessary to further improve communication through culturally appropriate educational materials and programs. These strategies may help to overcome the barriers in the treatment of type 2 diabetes in Hispanic/Latino patients.

Understanding the Hispanic/Latino patient

The Hispanic/Latino population is the largest minority group in the United States, representing approximately 16% of the population in 2010. The US Census Bureau defines Hispanic/Latino origin as ethnicity, which tends to be associated with culture and is distinct from race. Based on the US Census Bureau classifications, Hispanics/Latinos have at least 3 main racial backgrounds (white, black, and Native Indian), with the combination and proportion differing among Hispanic/Latino subgroups. The reflection of these racial differences in genetic ancestry partly explains why biological characteristics differ among Hispanic/Latino subgroups. Partly as a result of variations in biological characteristics, the risk of type 2 diabetes mellitus varies among Hispanic/Latino subgroups. According to data from the 1982 to 1984 Hispanic Health and Nutrition Examination Survey (HHANES), the prevalence of diagnosed and undiagnosed type 2 diabetes among adults aged 45 to 74 years was higher in Mexican Americans (23.9%) and Puerto Ricans (26.1%) compared with Cubans (15.8%). In addition to genetics, there are multiple social and cultural factors that affect the prevalence and course of type 2 diabetes in Hispanic/Latino individuals. Although certain aspects of Hispanic/Latino culture may become barriers in the management of type 2 diabetes in this population, these cultural characteristics may also represent an opportunity for prevention and/or improvement of care. It is important for healthcare providers to have an understanding and appreciation of Hispanic/Latino culture in order to provide their Hispanic/Latino patients with healthcare that is culturally and socially appropriate. Only by considering genetic, social, and cultural factors can type 2 diabetes be successfully prevented, treated, and managed in Hispanic/Latino patients.

Unmet needs in Hispanic/Latino patients with type 2 diabetes mellitus

In the United States, the prevalence of adults who are overweight or obese is higher in Hispanics/Latinos compared with non-Hispanic whites. In addition, data from the National Health and Nutrition Examination Survey (NHANES) indicate that the prevalence of type 2 diabetes mellitus is consistently greater in racial/ethnic minority groups, such as Hispanics/Latinos, compared with non-Hispanic whites. In fact, data from the Centers for Disease Control and Prevention (CDC) from 2007 to 2009 suggest that the prevalence of type 2 diabetes is almost twice as high in Hispanics/Latinos compared with non-Hispanic whites (11.8% vs. 7.1%, respectively). Although genetics plays a role in the increased prevalence of type 2 diabetes in Hispanics/Latinos, cultural and environmental factors also contribute. In addition to the increased prevalence of type 2 diabetes in Hispanics/Latinos, evidence suggests that the patients in this population are often undertreated and, therefore, less likely to achieve control of their glucose, blood pressure, and lipid levels. Because individuals with type 2 diabetes have a 2- to 4-fold increased risk of cardiovascular disease compared with individuals with normal glucose levels, there is consensus that targeting environmental factors, particularly the development of obesity at an early age, is the most cost-effective approach to prevent the development of type 2 diabetes and its broad spectrum of complications, including cardiovascular disease. Cultural and socioeconomic barriers, such as language, cost, and access to goods and services, must be overcome to improve management of type 2 diabetes in this high-risk population. By increasing healthcare provider awareness and the availability of programs tailored to Hispanic/Latino individuals, the current treatment gap among ethnic minorities in the United States will progressively narrow, and eventually, disappear.

Impact of socioeconomic status and sociodemographic factors on melanoma presentation among ethnic minorities

Minority melanoma patients have worse survival. In this study, we evaluated the impact of socioeconomic and demographic factors on minority melanoma patients presenting to two different New York City hospitals (one public and one private) managed by the same multidisciplinary team. Sociodemographic and clinicopathologic characteristics were retrieved for melanoma patients presenting to Bellevue Hospital Center (BHC), a public hospital, and the New York University Cancer Institute (NYUCI), a private cancer center. Socioeconomic data was obtained from the United States Census Bureau database. The Kruskal-Wallis and chi-square tests were used to evaluate the associations between race/ethnicity and continuous and categorical variables (e.g. income, stage at presentation), respectively. Minorities comprised 2% (27/1296) of melanoma patients at the NYUCI compared to 42% (50/119) at BHC. Those presenting to the NYUCI were more likely to have a higher median household income (P = 0.05), a higher educational level (P = 0.04), and an earlier stage at presentation (P = 0.02) than those at BHC. NYUCI patients were predominantly covered by commercial insurance (70%), whereas Medicaid (62%) was common among BHC patients. Only 19% of Hispanic patients at BHC chose English as their preferred language. Our data demonstrate that language and health care system factors affect melanoma presentation in minorities.

Wide disparity in genetic admixture among Mexican Americans from San Antonio, TX

We studied 706 participants of the San Antonio Family Diabetes Study (SAFDS) and 586 male samples from the San Antonio Center for Biomarkers of Risk of Prostate Cancer (SABOR) and used 64 ancestry informative markers to compare admixture proportions between both groups. Existence of population substructure was demonstrated by the excess association of unlinked markers. In the SAFDS sample, ancestral proportions were estimated at 50.2 ± 0.6% European, 46.4 ± 0.6% Native American, and 3.1 ± 0.2% West African. For the SABOR sample, the proportions were 58.9 ± 0.7%, 38.2 ± 0.7%, and 2.9 ± 0.2%, respectively. Additionally, in the SAFDS subjects a highly significant negative correlation was found between individual Native American ancestry and skin reflectance (R(2) = 0.07, P= 0.00006). The correlation was stronger in males than in females but clearly showed that ancestry only accounts for a small percentage of the variation in skin color and, conversely, that skin reflectance is not a robust surrogate for genetic admixture. Furthermore, a substantial difference in substructure is present in the two cohorts of Mexican American subjects from the San Antonio area in Texas, which emphasizes that genetic admixture estimates should be accounted for in association studies, even for geographically related subjects.

Taking a broad approach to public health program adaptation: adapting a family-based diabetes education program

Diabetes health disparities among Hispanic populations have been countered with federally funded health promotion and disease prevention programs. Dissemination has focused on program adaptation to local cultural contexts for greater acceptability and sustainability. Taking a broader approach and drawing on our experience in Mexican American communities at the U.S.-Mexico Border, we demonstrate how interventions are adapted at the intersection of multiple cultural contexts: the populations targeted, the community- and university-based entities designing and implementing interventions, and the field team delivering the materials. Program adaptation involves negotiations between representatives of all contexts and is imperative in promoting local ownership and program sustainability.

Differences in albuminuria between Hispanics and whites: an evaluation by genetic ancestry and country of origin: the multi-ethnic study of atherosclerosis

BACKGROUND

Reports show higher prevalence of albuminuria among Hispanics compared with whites. Differences by country of origin or genetic background are unknown.

METHODS AND RESULTS

In Multi-Ethnic Study of Atherosclerosis, we studied the associations of both genetic ancestry and country of origin with albumin to creatinine ratio among 1417 Hispanic versus white participants using multivariable linear regression and back transforming beta coefficients into relative difference (%RD, 95% CI). Percentage European, Native American, and African ancestry components for Hispanics were estimated using genetic admixture analysis. The proportions of European, Native American, and African genetic ancestry differed significantly by country of origin (P<0.0001); Mexican/Central Americans had the highest Native American (41+/-13%), Puerto Ricans had the highest European (61+/-15%), and Dominicans had the highest African (39+/-21%) ancestry. Hispanic ethnicity was associated with higher albumin/creatinine ratio compared with whites, but the association varied with the country of origin (adjusted P interaction=0.04). Mexican/Central Americans and Dominicans had higher albumin/creatinine ratio compared with whites after adjustment (RD 19%, 2% to 40% and RD 27%, 1% to 61%), but not Puerto Ricans (RD 8%, -12% to 34%). Higher Native American ancestry was associated with higher albuminuria after age and sex adjustment among all Hispanics (RD 11%, 1% to 21%) but was attenuated after further adjustment. Higher European ancestry was independently associated with lower albumin/creatinine ratio among Puerto Ricans (-21%, -34% to -6%) but not among Mexican/Central Americans and Dominicans.

CONCLUSIONS

Hispanics are a heterogeneous group with varying genetic ancestry. Risks of albuminuria differ across the country of origin groups. These differences may be due, in part, to differences in genetic ancestral components.

Left ventricular mass and ventricular remodeling among Hispanic subgroups compared with non-Hispanic blacks and whites: MESA (Multi-ethnic Study of Atherosclerosis)

OBJECTIVES

The purpose of this study was to examine the prevalence of left ventricular hypertrophy (LVH) and left ventricular (LV) remodeling patterns within Hispanic subgroups compared with non-Hispanic whites in the MESA (Multi-Ethnic Study of Atherosclerosis).

BACKGROUND

Hispanics are the largest and fastest-growing ethnic minority in the U.S., but there are no data on LVH and LV geometry among Hispanic subgroups.

METHODS

Cardiac magnetic resonance imaging was performed in 4,309 men and women age 45 to 84 years without clinical cardiovascular disease. Hispanics were categorized into subgroups based on self-reported ancestry. LVH was defined as the upper 95th percentile of indexed LV mass in a reference normotensive, nondiabetic, nonobese population, and LV remodeling according to the presence/absence of LVH and abnormal/normal LV mass to LV end-diastolic volume ratio.

RESULTS

Among Hispanic participants, 574 were of Mexican origin, 329 were of Caribbean origin, and 161 were of Central/South American origin. On unadjusted analysis, only Caribbean-origin Hispanics (prevalence ratio = 1.2; 95% confidence interval [CI]: 1.03 to 1.4) had greater prevalence of hypertension than non-Hispanic whites. Hispanic subgroups were more likely to have LVH than non-Hispanic whites after adjustment for hypertension and other covariates (Caribbean-origin Hispanics = odds ratio [OR]: 1.8, 95% CI: 1.1 to 3.0; Mexican-origin Hispanics = OR: 2.2, 95% CI: 1.4 to 3.3; Central/South Americans = OR: 1.5, 95% CI: 0.7 to 3.1). All Hispanic subgroups also had a higher prevalence of concentric and eccentric hypertrophy compared with non-Hispanic whites (p < 0.001).

CONCLUSIONS

Caribbean-origin Hispanics had a higher prevalence of LVH and abnormal LV remodeling compared with non-Hispanic whites. A higher prevalence of LVH and abnormal LV remodeling was also observed among Mexican-origin Hispanics, despite a lower prevalence of hypertension. Differences among Hispanic subgroups regarding LVH and LV remodeling should be taken into account when evaluating cardiovascular risk in this population.

Paucity of skeletal manifestations in Hispanic families with FBN1 mutations

Marfan syndrome (MFS) is an autosomal dominant condition with pleiotropic manifestations involving the skeletal, ocular, and cardiovascular systems. The diagnosis is based primarily on clinical involvement of these and other systems, referred to as the Ghent criteria. We have identified three Hispanic families from Mexico with cardiovascular and ocular manifestations due to novel FBN1 mutations but with paucity of skeletal features. The largest family, hMFS001, had a frameshift mutation in exon 24 (3075delC) identified as the cause of aortic disease in the family. Assessment of eight affected adults revealed no major skeletal manifestation of MFS. Family hMFS002 had a missense mutation (R1530C) in exon 37. Four members fulfilled the criteria for ocular and cardiovascular phenotype but lacked skeletal manifestations. Family hMFS003 had two consecutive missense FBN1 mutations (C515W and R516G) in exon 12. Eight members fulfilled the ocular criteria for MFS and two members had major cardiovascular manifestations, however none of them met criteria for skeletal system. These data suggest that individuals of Hispanic descent with FBN1 mutations may not manifest skeletal features of the MFS to the same extent as Caucasians. We recommend that echocardiogram, ocular examination and FBN1 molecular testing be considered for any patients with possible MFS even in the absence of skeletal features, including Hispanic patients.

Melanoma arising in African-, Asian-, Latino- and Native-American populations

This review highlights melanoma trends observed among African-, Asian-, Latino- and Native-American populations. Melanoma is the most lethal form of skin cancer, accounting for about 75% of all skin cancer deaths. Generally, incidence rates increase with age, peak after age 40, and are greater in men than women. However, these trends do not reflect what is typically seen in minority ethnic groups, where incidence rates are lower. In addition, for some groups, relative disease-specific survival also is lower compared with European-Americans. Melanomas in minority populations also tend to appear in atypical locations and are of unclear etiology. To improve our understanding of the causes of melanoma arising in ethnic minority populations future research efforts are needed. In addition, the general lack of awareness of this disease entity among minority populations and the fact that certain ethnic groups tend to present with advanced disease further highlight the need for educational programs for both patients and health care professionals.

ADME transcriptome in Hispanic versus White donor livers: Evidence of a globally enhanced NR1I3 (CAR, constitutive androstane receptor) gene signature in Hispanics

Previous studies have found that, compared with Whites, Hispanic donor livers had elevated expression of CYP2 enzymes, gene products regulated by the constitutive androstane receptor (CAR). The objectives of the current study were to determine (1) the CAR activation signature in human liver (2) whether other drug detoxification (absorption, distribution, metabolism and excretion (ADME)) genes were differentially expressed in Hispanic versus White livers, and (3) the extent of overlap in the CAR and Hispanic liver transcriptomes. The CAR transcriptome (ADME genes differentially expressed following phenobarbital versus vehicle treatment of human hepatocytes) and the Hispanic liver transcriptome (ADME genes differentially expressed in Hispanic versus White livers) were identified using Affymetrix oligonucleotide arrays. Quantitative real-time polymerase chain reaction (PCR) was used to verify candidate genes in a larger sample size. Comparison of the CAR and Hispanic liver ADME transcriptomes revealed a significant association between the gene changes. Sixty-four per cent of the ADME genes induced more than twofold by phenobarbital were also induced in Hispanics, and 14% of the ADME genes repressed more than twofold by phenobarbital were repressed in Hispanics. In conclusion, compared with Whites, Hispanic donor livers have increased expression of many genes that are transcriptionally regulated by CAR. This result has practical implications to the drug treatment of Hispanic patients.

Physiogenomic analysis of the Puerto Rican population

AIMS

Admixture in the population of the island of Puerto Rico is of general interest with regards to pharmacogenetics to develop comprehensive strategies for personalized healthcare in Latin Americans. This research was aimed at determining the frequencies of SNPs in key physiological, pharmacological and biochemical genes to infer population structure and ancestry in the Puerto Rican population.

MATERIALS & METHODS

A noninterventional, cross-sectional, retrospective study design was implemented following a controlled, stratified-by-region, random sampling protocol. The sample was based on birthrates in each region of the island of Puerto Rico, according to the 2004 National Birth Registry. Genomic DNA samples from 100 newborns were obtained from the Puerto Rico Newborn Screening Program in dried-blood spot cards. Genotyping using a physiogenomic array was performed for 332 SNPs from 196 cardiometabolic and neuroendocrine genes. Population structure was examined using a Bayesian clustering approach as well as by allelic dissimilarity as a measure of allele sharing.

RESULTS

The Puerto Rican sample was found to be broadly heterogeneous. We observed three main clusters in the population, which we hypothesize to reflect the historical admixture in the Puerto Rican population from Amerindian, African and European ancestors. We present evidence for this interpretation by comparing allele frequencies for the three clusters with those for the same SNPs available from the International HapMap project for Asian, African and European populations.

CONCLUSION

Our results demonstrate that population analysis can be performed with a physiogenomic array of cardiometabolic and neuroendocrine genes to facilitate the translation of genome diversity into personalized medicine.

Serum 25-hydroxyvitamin D and bone mineral density among Hispanic men

There are few data on the skeletal health of Hispanic men. We observed differences in vitamin D deficiency and low BMD between Hispanic ethnic subgroups that persisted with adjustment for risk factors. Our data indicate a substantial burden of low BMD and vitamin D deficiency among Hispanic men.

INTRODUCTION

Disparities within ethnic groups are generally ignored, but in evolving populations they may have implications for public health. We examined ethnic variation in serum 25-hydroxyvitamin D [25(OH)D] and bone mineral density (BMD) among Hispanic American men.

METHODS

Three hundred and fifty-eight Hispanic males 30 to 79 years of age were studied. Logistic regression models assessed variation in odds of vitamin D deficiency (<20 ng/mL) and low BMD (T-score<-1) by ethnicity, with and without adjustment for risk factors (age, smoking, occupation, physical activity, body mass index, and sunlight exposure).

RESULTS

Vitamin D deficiency was most common among Puerto Rican (26%), compared with Dominican (21%), Central American (11%), and South American (9%) men. Percentages with low BMD were: South American (44%), Puerto Rican (34%), Dominican (29%), and Central American (23%). Adjustment for age and risk factors failed to account for Hispanic subgroup differences in vitamin D deficiency and low BMD. Population estimates indicate a substantial burden of low BMD and vitamin D deficiency among Hispanic men.

CONCLUSIONS

Our findings underscore the importance of examining the skeletal health of Hispanic subgroups, and suggest that a considerable number of Hispanic men may be at elevated risk of fracture and vitamin D deficiency.

The biologistical construction of race: 'admixture' technology and the new genetic medicine

This paper presents an ethnographic case study of the use of race in two interconnected laboratories of medical genetics. Specifically, it examines how researchers committed to reducing health disparities in Latinos with asthma advance hypotheses and structure research to show that relative frequencies of genetic markers characterize commonly understood groupings of race. They do this first by unapologetically advancing the idea that peoples whom they take to be of the 'Old World', or 'Africans', 'Europeans', 'East Asians', and 'Native Americans', can serve as putatively pure reference populations against which genetic risk for common diseases such as asthma can be calculated for those in the 'New World'. Technologically, they deploy a tool called ancestry informative markers (AIMs), which are a collection of genetic sequence variants said to differ in present-day West Africans, East Asians, Europeans, and (ideally Pre-Columbian) Native Americans. I argue that this technology, compelling as it may be to a range of actors who span the political spectrum, is, at base, designed to bring about a correspondence of familiar ideas of race and supposed socially neutral DNA. This correspondence happens, in part, as the scientists in question often bracket the environment while privileging racialized genetic variance as the primary source of health disparities for common disease, in this case between Mexicans and Puerto Ricans with asthma. With their various collaborators, these scientists represent a growing movement within medical genetics to re-consider race and 'racial admixture' as biogenetically valid points of departure. Furthermore, many actors at the center of this ethnography focus on race as a function of their personal identity politics as scientists of color. This to say, they are driven not by racist notions of human difference, but by a commitment to reduce health disparities and to include 'their' communities in what they describe as the 'genetic revolution'.

Characteristics of a spina bifida population including North American Caucasian and Hispanic individuals

BACKGROUND

Meningomyelocele (MM) is a common human birth defect. MM is a disorder of neural development caused by contributions from genes and environmental factors that result in the NTD and lead to a spectrum of physical and neurocognitive phenotypes.

METHODS

A multidisciplinary approach has been taken to develop a comprehensive understanding of MM through collaborative efforts from investigators specializing in genetics, development, brain imaging, and neurocognitive outcome. Patients have been recruited from five different sites: Houston and the Texas-Mexico border area; Toronto, Canada; Los Angeles, California; and Lexington, Kentucky. Genetic risk factors for MM have been assessed by genotyping and association testing using the transmission disequilibrium test.

RESULTS

A total of 509 affected child/parent trios and 309 affected child/parent duos have been enrolled to date for genetic association studies. Subsets of the patients have also been enrolled for studies assessing development, brain imaging, and neurocognitive outcomes. The study recruited two major ethnic groups, with 45.9% Hispanics of Mexican descent and 36.2% North American Caucasians of European descent. The remaining patients are African-American, South and Central American, Native American, and Asian. Studies of this group of patients have already discovered distinct corpus callosum morphology and neurocognitive deficits that associate with MM. We have identified maternal MTHFR 667T allele as a risk factor for MM. In addition, we also found that several genes for glucose transport and metabolism are potential risk factors for MM.

CONCLUSIONS

The enrolled patient population provides a valuable resource for elucidating the disease characteristics and mechanisms for MM development.

Genome-wide distribution of ancestry in Mexican Americans

Migrations to the new world brought together individuals from Europe, Africa and the Americans. Inter-mating between these migrant and indigenous populations led to the subsequent formation of new admixed populations, such as African and Latino Americans. These unprecedented events brought together genomes that had evolved independently on different continents for tens of thousands of years and presented new environmental challenges for the indigenous and migrant populations, as well as their offspring. These circumstances provided novel opportunities for natural selection to occur that could be reflected in deviations at specific locations from the genome-wide ancestry distribution. Here we present an analysis examining European, Native American and African ancestry based on 284 microsatellite markers in a study of Mexican Americans from the Family Blood Pressure Program. We identified two genomic regions where there was a significant decrement in African ancestry (at 2p25.1, p < 10(-8) and 9p24.1, p < 2 x 10(-5)) and one region with a significant increase in European ancestry (at 1p33, p < 2 x 10(-5)). These locations may harbor genes that have been subjected to natural selection after the ancestral mixing giving rise to Mexicans.

Genome-wide SNP typing reveals signatures of population history

Single-nucleotide polymorphism (SNP) arrays have become a popular technology for disease-association studies, but they also have potential for studying the genetic differentiation of human populations. Application of the Affymetrix GeneChip Human Mapping 500K Array Set to a population of 102 individuals representing the major ethnic groups in the United States (African, Asian, European, and Hispanic) revealed patterns of gene diversity and genetic distance that reflected population history. We analyzed allelic frequencies at 388,654 autosomal SNP sites that showed some variation in our study population and 10% or fewer missing values. Despite the small size (23-31 individuals) of each subpopulation, there were no fixed differences at any site between any two subpopulations. As expected from the African origin of modern humans, greater gene diversity was seen in Africans than in either Asians or Europeans, and the genetic distance between the Asian and the European populations was significantly lower than that between either of these two populations and Africans. Principal components analysis applied to a correlation matrix among individuals was able to separate completely the major continental groups of humans (Africans, Asians, and Europeans), while Hispanics overlapped all three of these groups. Genes containing two or more markers with extraordinarily high genetic distance between subpopulations were identified as candidate genes for health differences between subpopulations. The results show that, even with modest sample sizes, genome-wide SNP genotyping technologies have great promise for capturing signatures of gene frequency difference between human subpopulations, with applications in areas as diverse as forensics and the study of ethnic health disparities.

Genome-wide screen for asthma in Puerto Ricans: evidence for association with 5q23 region

While the number of success stories for mapping genes associated with complex diseases using genome-wide association approaches is growing, there is still much work to be done in developing methods for such studies when the samples are collected from a population, which may not be homogeneous. Here we report the first genome-wide association study to identify genes associated with asthma in an admixed population. We genotyped 96 Puerto Rican moderate to severe asthma cases and 88 controls as well as 109 samples representing Puerto Rico's founding populations using the Affymetrix GeneChip Human Mapping 100K array sets. The data from samples representing Puerto Rico's founding populations was used to identify ancestry informative markers for admixture mapping analyses. In addition, a genome-wide association analysis using logistic regression was performed on the data. Although neither admixture mapping nor regression analysis gave any significant association with asthma after correction for multiple testing, an overlap analysis using the top scoring SNPs from different methods suggested chromosomal regions 5q23.3 and 13q13.3 as potential regions harboring genes for asthma in Puerto Ricans. The validation analysis of these two regions in 284 Puerto Rican asthma trios gave significant association for the 5q23.3 region. Our results provide strong evidence that the previously linked 5q23 region is associated with asthma in Puerto Ricans. The detection of causative variants in this region will require fine mapping and functional validation.

Genetics of asthma: potential implications for reducing asthma disparities

Although genetic factors may partly explain the differences in asthma prevalence, morbidity, and mortality among ethnic groups in the United States, few studies of the genetics of asthma have included members of ethnic minority groups. Only one genome-wide linkage analysis of asthma and/or asthma-related phenotypes (conducted by the Collaborative Study on the Genetics of Asthma) has included any members of ethnic minority populations. The interpretation of the findings of genetic association studies of asthma in ethnic minority groups is complicated by reduced statistical power due to small sample sizes; the failure to correct for multiple comparisons; a lack of homogeneity of the populations studied with regard to area of residence, ancestral background, and/or country of origin; a lack of measurement of relevant environmental exposures; and (for case-control studies of genetic association) a lack of detection and control of potential population stratification. Genetic studies may improve our understanding of asthma and lead to new methods to prevent, diagnose, and treat this disease. Limited study of asthma genetics in ethnic minority populations is unacceptable, as it may prevent these groups from benefiting from future developments in asthma management and thus widen existing disparities in asthma care. Future genetic association studies of asthma among ethnic minorities in the United States should include large samples of populations that have been adequately defined with regard to area of residence, self-designated ancestry, and country of origin. These studies should also include an adequate assessment of potentially relevant environmental exposures and (for case-control association studies) population stratification.

Confounding in genetic association studies and its solutions

An association study can be used to investigate how individuals with unique genetic variants respond to a drug treatment. In an association study, individuals may come from different ethnic groups or an admixed population. The heterogeneity of genetic backgrounds among individuals in association studies may lead to false-positive or false-negative results. Confounding caused by population structure and recent admixture may be one major factor that contributes to the lack of replication of association study results. Confounding can be detected and adjusted. Major methods that adjust for population stratification are described and explained in this chapter. Their advantages and disadvantages are discussed.

Identification of type 2 diabetes genes in Mexican Americans through genome-wide association studies

OBJECTIVE

The objective of this study was to identify DNA polymorphisms associated with type 2 diabetes in a Mexican-American population.

RESEARCH DESIGN AND METHODS

We genotyped 116,204 single nucleotide polymorphisms (SNPs) in 281 Mexican Americans with type 2 diabetes and 280 random Mexican Americans from Starr County, Texas, using the Affymetrix GeneChip Human Mapping 100K set. Allelic association exact tests were calculated. Our most significant SNPs were compared with results from other type 2 diabetes genome-wide association studies (GWASs). Proportions of African, European, and Asian ancestry were estimated from the HapMap samples using structure for each individual to rule out spurious association due to population substructure.

RESULTS

We observed more significant allelic associations than expected genome wide, as empirically assessed by permutation (14 below a P of 1 x 10(-4) [8.7 expected]). No significant differences were observed between the proportion of ancestry estimates in the case and random control sets, suggesting that the association results were not likely confounded by substructure. A query of our top approximately 1% of SNPs (P < 0.01) revealed SNPs in or near four genes that showed evidence for association (P < 0.05) in multiple other GWAS interrogated: rs979752 and rs10500641 near UBQLNL and OR52H1 on chromosome 11, rs2773080 and rs3922812 in or near RALGPS2 on chromosome 1, and rs1509957 near EGR2 on chromosome 10.

CONCLUSIONS

We identified several SNPs with suggestive evidence for replicated association with type 2 diabetes that merit further investigation.