Polynesian Ancestry Linked to Obesity in Study of Native Hawaiians
Native Hawaiians of Polynesian ancestry are at an increased risk of obesity, heart failure, and type 2 diabetes, a study has found.
The greater risk of diabetes is linked to a genetic variant that is uniquely prevalent in Native Hawaiians.
The study, “The impact of global and local Polynesian genetic ancestry on complex traits in Native Hawaiians,” appeared in the journal PLOS Genetics.
Compared to Hawaiian citizens of European or Japanese descent, Native Hawaiians have a considerably higher risk of obesity, type 2 diabetes, cardiovascular disease, and other cardiometabolic risk factors such as hypertension. Although non-genetic factors, such as socioeconomic status and diet, influence the development of these conditions, differing genetic profiles may contribute to the disparity in disease risk of Native Hawaiians from different ancestries.
Despite genetics playing a known role in obesity and related conditions, these factors have not been well-characterized in indigenous populations such as Native Hawaiians, at least partially because of the small population size.
“Native Hawaiians really have been understudied from a genetic perspective,” Charleston Chiang, PhD, assistant professor at the University of Southern California and senior author of the study, said in a university press release. “My team focuses on looking at the genetic component of health risk within geographically diverse populations.”
Chiang and his colleagues investigated the genetic factors underlying increased disease risk in Native Hawaiians of Polynesian ancestry by analyzing genetic variations in the population. Genetic data from 3,940 self-identified Native Hawaiians from the Multiethnic Cohort Study were used to develop a model to determine the relationship between ancestry and disease risk.
Results showed that Polynesian ancestry was strongly associated with an elevated risk of obesity, type 2 diabetes, and heart failure, as well as higher body mass index (BMI, a measure of body fat) and lower levels of high-density lipoprotein (HDL) or “good” cholesterol. After adjusting for BMI, type 2 diabetes and heart failure showed a linear association with Polynesian ancestry such that every 10% increase in Polynesian genetic ancestry corresponded with an 8.6% increased risk of diabetes and an 11% greater risk of heart failure.
“While we needed to quantify the proportion of Polynesian ancestry in order to perform our research, we do not want to give the impression that this is a way for people to define their membership in the community based on some arbitrary threshold,” said Chiang.
Interestingly, East Asian ancestry in Native Hawaiians was associated with a greater risk of type 2 diabetes, high blood fat, and hypertension, but also with a lower risk of obesity and lower BMI. In fact, after adjusting for BMI, East Asian ancestry had a greater effect than Polynesian ancestry on type 2 diabetes risk. This suggests that East Asian and Polynesian ancestry both impact disease risk in Native Hawaiians.
Socioeconomic status was significantly associated with the same risk factors as Polynesian ancestry, namely BMI, obesity, HDL level, type 2 diabetes, and heart failure, and appears to account for some but not all of the risk. These results indicate that Polynesian genetic risk factors at least partly explain the greater disease risk in Native Hawaiians, said the researchers.
Further analysis found an association between Polynesian ancestry and BMI in individuals without type 2 diabetes, such that a 10% increase in Polynesian ancestry corresponded with a 0.51 unit increase in BMI. Notably, no such relationship was observed in those with type 2 diabetes.
Then, the team found that a genetic variant on chromosome 6 was significantly associated with type 2 diabetes. The variant, called rs370140172, is uniquely prevalent, at 24.2%, in people with Polynesian ancestry, compared with 11.2% in Native Hawaiians, 0% in Europeans, 0.9% in East Asians, and 1.2% in Southeast Asians included in the study.
The variant was significantly less frequent (8.7%) in an independent Polynesian population from Samoa. However, the association between rs370140172 and type 2 diabetes could not be replicated in the Samoan group due to the small sample size.
“Our results suggest future studies could identify population-specific genetic susceptibility factors that may elucidate underlying biological mechanisms and reducing the disparity in disease risks in Polynesian populations,” the researchers wrote.
Added Chiang: “Genetics is a window into understanding the biology behind these diseases. Genetics does not determine everything, and it doesn’t necessarily even amount to the majority of the disparity in risk.”