Mixed Race Studies

The Great Migration and African-American Genomic Diversity

PLOS Genetics
2016-05-27
27 pages
DOI: 10.1371/journal.pgen.1006059

Soheil Baharian
Department of Human Genetics
McGill University, Montreal, Quebec, Canada
Genome Quebec Innovation Centre, Montreal, Quebec, Canada

Maxime Barakatt
McGill University and Genome Quebec Innovation Centre, Montreal, Quebec, Canada

Christopher R. Gignoux
Department of Genetics
Stanford University School of Medicine, Stanford, California

Suyash Shringarpure
Department of Genetics
Stanford University School of Medicine, Stanford, California

Jacob Errington
Department of Human Genetics
McGill University, Montreal, Quebec, Canada
Genome Quebec Innovation Centre, Montreal, Quebec, Canada

William J. Blot
Division of Epidemiology
Vanderbilt University School of Medicine, Nashville, Tennessee
International Epidemiology Institute, Rockville, Maryland

Carlos D. Bustamante
Department of Genetics
Stanford University School of Medicine, Stanford, California

Eimear E. Kenny
Department of Genetics and Genomic Sciences
The Icahn School of Medicine at Mount Sinai, New York, New York

Scott M. Williams
Department of Genetics
Institute for Quantitative Biomedical Sciences, Dartmouth College, Hanover, New Hampshire

Melinda C. Aldrich
Division of Epidemiology, Department of Thoracic Surgery
Vanderbilt University School of Medicine, Nashville, Tennessee

Simon Gravel
Department of Human Genetics
McGill University, Montreal, Quebec, Canada
Genome Quebec Innovation Centre, Montreal, Quebec, Canada

Fig 3. Pairwise genetic relatedness across US census regions among (A) African-Americans, (B) European-Americans, and (C) African-Americans and European-Americans. (D) Census-based prediction for African-Americans (see Materials and Methods). On each map, the line connecting two regions shows the average relatedness between individuals in those regions, and the thickness and opacity of the lines are on a linear scale between the minimum and maximum values shown above the map. Relatedness between regions with fewer than 10,000 possible pairs of individuals is not shown (see Materials and Methods for details). All numbers are in units of cM. (E) Decay of average IBD (shown in logarithmic scale) as a function of distance using IBD segments of length 18cM or longer from HRS (dots), compared to the analytical model (lines).

Abstract

We present a comprehensive assessment of genomic diversity in the African-American population by studying three genotyped cohorts comprising 3,726 African-Americans from across the United States that provide a representative description of the population across all US states and socioeconomic status. An estimated 82.1% of ancestors to African-Americans lived in Africa prior to the advent of transatlantic travel, 16.7% in Europe, and 1.2% in the Americas, with increased African ancestry in the southern United States compared to the North and West. Combining demographic models of ancestry and those of relatedness suggests that admixture occurred predominantly in the South prior to the Civil War and that ancestry-biased migration is responsible for regional differences in ancestry. We find that recent migrations also caused a strong increase in genetic relatedness among geographically distant African-Americans. Long-range relatedness among African-Americans and between African-Americans and European-Americans thus track north- and west-bound migration routes followed during the Great Migration of the twentieth century. By contrast, short-range relatedness patterns suggest comparable mobility of ∼15–16km per generation for African-Americans and European-Americans, as estimated using a novel analytical model of isolation-by-distance.

Author Summary

Genetic studies of African-Americans identify functional variants, elucidate historical and genealogical mysteries, and reveal basic biology. However, African-Americans have been under-represented in genetic studies, and relatively little is known about nation-wide patterns of genomic diversity in the population. Here, we study African-American genomic diversity using genotype data from nationally and regionally representative cohorts. Access to these unique cohorts allows us to clarify the role of population structure, admixture, and recent massive migrations in shaping African-American genomic diversity and sheds new light on the genetic history of this population.

Read the entire article here.

Study explores race differences of lung cancer risk

Vanderbilt University Medical Center Reporter
2013-08-01

Mimi Eckhard

Vanderbilt research scientist Melinda Aldrich, Ph.D., MPH, has been awarded a National Institutes of Health Academic Career Award to investigate some of the genetic secrets behind a greater risk of lung cancer among African-Americans compared with other racial and ethnic groups.

Aldrich, assistant professor of Thoracic Surgery and Epidemiology, will study the genetic ancestry of African-Americans to identify the genetic and environmental risk factors associated with a higher incidence of lung cancer in this population.

To date, this represents the largest study of African-Americans with lung cancer.

Though smoking is certainly a well-documented risk factor for lung cancer, it does not explain the racial disparity in lung cancer risk. Therefore, Aldrich believes a genetic difference may lie at the root of the problem…

…This five-year research study will be the largest to examine the genetics of lung cancer in a population whose ancestry is mixed and separated by thousands of years. African-Americans have ancestry in both Africa and Europe, and genetic mapping could identify common key regions that contribute to racial differences in lung cancer incidence…

Read the entire article here.

Genetic screening may redefine medical treatments

KGO-TV San Francisco, California
2010-07-07

Carolyn Johnson, Co-Anchor
KGO-TV

SAN FRANCISCO (KGO) — New research out of UCSF [University of California, San Francisco] shows that tracking a patient’s genetic ancestry can improve the diagnosis of asthma and other lung diseases. The results could have broader implications for other diseases that also rely on standard benchmarks such as race, gender and age.

Doctor’s office visits are the norm for 9-year-old Shamatay Hayes. She was diagnosed with asthma at age 2, something she and her mom have struggled to keep under control.

“It is challenging,” her mother says.

At San Francisco General Hospital and at asthma clinic across the country, Shamatay’s lung function is tracked using standard benchmarks such as age, gender and race. But, researchers say there is now a better way.

“So, what we can now do with modern techniques is estimate what a person’s ancestry is or what their heritage is using a series of genetic markers,” says UCSF researcher Dr. Melinda Aldrich.

The genetic markers more accurately determine lung function rather than a patient’s self-identification as simply white, black or Hispanic.

“With increasing African ancestry, we saw a decrement in lung function,” says UCSF associate professor Dr. Esteban Burchar…

…”We’ve had people contact us who were supremacists that said you know what you’re doing is validating what we believe,” he says.

But, the research actually tells a different story.

“Most of us, all of us in fact, are racially mixed,” he says. “We have a very rich heritage and what we’re doing is acknowledging that mixture and incorporating it into our clinical assessments.”…

Read the entire article and view the video clip here.