A genetic study published in the journal Science rebuilds the history of Mexican Pre-Columbian populations and characterises the genetic structure of present-day Mexican populations. The study identifies the existence of different Native American gene clusters in proportions that vary according to the geographical origin of Mexican individuals. Marc via, from the Department of Psychiatry and Clinical Psychobiology and the Institute for Brain, Cognition and Behaviour of University of Barcelona (IR3C) participated in the study.
To study gene variation in human species
Characterising human gene variation patterns is key for understanding the demographic history of human populations but it is also crucial to design and interpret clinical and medical genetic studies.
"In this context, Native American populations own some genetic particularities that make them interesting. One the one hand, they are genetically quite similar as the size of samples that populated the American continent is small. But, on the other hand, they are also very different among them due to geographic isolation", explains Mar Via, who developed the study after his postdoctoral stay at the laboratory led by the expert Esteban González at the University of California, San Francisco (USCF).
Mexico, a cross of civilizations
Furthermore, present-day American indigenous populations may harbour local private alleles rare or absent elsewhere, including functional and medically relevant variants. Mexico serves as an important focal point for such analyses because it harbours one of the largest sources of pre-Columbian diversity and has a long history of complex civilizations.
The new study published in the journal Science analysed a group of genetic markers that cover a great part of the genome and enabled to characterise the source population of each person's chromosome fragments. To be exact, nearly one million single nucleotide polymorphisms were analysed in over 1,000 individuals representing 20 indigenous and 11 mestizo Mexican populations. It is a pioneering study regarding the number of individuals and populations included.
Genetic differences among indigenous populations
"Among the results of the analysis of Mexican indigenous populations, high levels of gene variation are particularly noticeable in some groups. In other words, some groups were as differentiated as Europeans are from East-Asians. That enabled to estimate the effective size of these populations", stresses Marc Vila. "Moreover, some relationships among Native American groups and those settled along both coastlines of the country were observed", explains the researcher who participated in the design of the study and in the first phases of data analysis together with the co-authors of the study Andrés Moreno Estrada and Chris Gignoux.
This accurate characterization is important for population studies, but authors also proved its potential biomedical applications by analysing independent samples of Mexican children with asthma (one sample was collected in Mexico City and the other in California). The characterization of the genes provided by the different indigenous groups to each asthmatic individual showed that present-day Mexican populations have different standard measures of lung function depending on the Mexican indigenous group that has most contributed to its genetic heritage. These differences in lung function - established by means of the forced expiratory volume in 1 second (FEV1) - are relatively small but they may influence the diagnose of respiratory diseases or the establishment of medical disabilities.
Applying the results to biomedicine
"The study first proves that sub-continental ancestry many have an important impact on relevant biomedical characters", points out Marc Via, who also participated in the international consortium 1000 Genomes to produce an extensive public catalogue of the main DNA mutations that affect human health.
The study was set up within the collaborations between Esteban González Burchard and Carlos Bustamante (Faculty of Medicine, Stanford University) to study genetic diversity in present-day Latin-American populations and its impact on the study of complex diseases. The National Institute of Genomic Medicine (INMEGEN) in Mexico City supported the study.