Mexicans genetically predisposed to obesity, study says

Translated by Brian Schwarz

Originally published Thursday, August 2, 2012 in "La Jornada" (lajornada.unam.mx) and "Vanguardia" (vanguardia.com.mx) under the heading "Los mexicanos tienen predisposición genética a la obesidad, según estudio" by Emir Olivares Alonso.

Photo: Vanguardia archives

MEXICO CITY – Mexicans have a high predisposition to develop overweight and obesity, conditions which lead to chronic illness and metabolic complications. This is according various joint studies conducted by the Faculty of Chemistry (FQ) of the National Autonomous University of Mexico (UNAM) and the National Institute of Medical Sciences and Nutrition Salvador Zubirán and the National Institute of Genomic Medicine, Mexico.

The most relevant findings include the identification of a genetic variant of metabolic risks – exclusive to Mexicans – which change the function of the cholesterol transporter ABCA1 and provoke a lowering in the levels of good cholesterol, or HDL, which works to clean the arteries.

Samuel Canizales Quinteros, researcher at the FQ and work group coordinator, said that when this transporter functions well it generates normal to high levels of HDL, the particles of which possess anti-inflammatory properties and antioxidants. Also, he said, “people with good cholesterol tend to live longer.”

Researchers found a variant affecting Mexican indigenous and mestizo popopulations that provokes an amino acid (arginine to cysteine at position 230). The scientist added that studies have been done in groups of people from Africa, Asia and Europe and “in none have we seen this change”.

This mutation increases the risk of having obesity and if the pancreas is affected it causes inadequate secretion of insulin, thereby increasing the risk of developing diabetes.

The research team is now looking for other variants exclusive to America in order to explain why certain illnesses, like non-alcoholic fatty liver and type 2 diabetes among others, are more prevalent on the continent.

Canizales is also heading other projects related to the investigation of genes that increase the probability of obesity and overweight, given the rising number of cases and the related risk factors for developing diabetes, hypertension, non-alcoholic fatty liver and certain types of cancer.

One of the lines of investigation reveals that the FTO gene, linked to the amount of fat in the organism, the melanocortin-4 receptor (MC4R) and the convertase 1 protein (PCSK1), increases the risk of morbid or class III obesity nearly four times in Mexicans, but does not seem to cause such an increase for class I and II obesity, the most common types.

Another group is concerned with understanding what happens when fat accumulates in the liver; One of the other co-morbidities associated with obesity is non-alcoholic fatty liver, which can progress into complications like cirrhosis and hepatocarcinoma.

For this, one of the objectives raised in this analysis is determining non-invasive molecular markers, which allows for the identifications of subjects in risk of showing complications. In terms of affliction prevalence, the researcher estimated that it is present in around 70 percent of those who are obese, a rate that increases 90 percentage points if the individual is severely or morbidly obese.

Complex Disease

“Mexico occupies first place in childhood obesity, and in adults also counts among the top places on a global scale. As such, our study group includes more than 4,000 school aged children, which allows us to identify genetic and environmental risk factors.”

Canizales, who has for more than a decade been conducting projects focused on the obesity genome and related co-morbidities, admitted that the problem cannot be considered solely a genomic one; It is a complex disease shaped by many factors, like sedentary lifestyles, poor nutrition and genetic susceptibility.

The idea of collaborating in a multi-disciplinary way with other research institutions multiplies efforts for treating obesity and lowering obesity rates in the country.

“We hope that our results will be useful for the future development of diagnostic tests and preventative programs,” he said.