An extraordinary series of voyages that populated some of the most-remote islands in the Pacific left a genetic legacy that could have consequences for the health of Native Hawaiians and other Eastern Polynesian peoples today, new research suggests. Scientists using whole-genome sequencing to study DNA from people across Polynesia found that repeated migrations by relatively small groups created some of the strongest known "founder effects" in the world, increasing the prevalence of some rare genetic variants that can cause inherited diseases. The study, published in Science earlier this month, found that the genetic founder effects seen in Polynesian populations were at least 10 times stronger than those found among Finns, a population whose genetic history has been extensively studied and incorporated into genetic screening, which involves testing a person's DNA for variants that can increase the risk of inherited diseases.
Researchers analyzed whole-genome sequencing data from 1,050 people across French Polynesia and incorporated genetic data from Rapa Nui, Native Hawaiians, Samoans and Tongans. The findings suggest that Hawaiʻi and Rapa Nui, despite being roughly 7,000 kilometers apart, are particularly closely related genetically. The researchers concluded that both were probably settled by the same long-distance voyaging population with earlier ancestral roots in Mangareva.
The health implications stem from the founder effect. When a small group of people leaves a larger population to establish a new community, that group's descendants inherit only a fraction of the genetic diversity of the original population. By chance, a rare variant carried by one of those founders may, therefore, become more common among later generations.
That process was repeated as Polynesians moved from island to island. Each relatively small founding group carried only a portion of the genetic diversity of the population it came from. This allowed some rare genetic variants to become more common among their descendants, with the strongest effects seen in remote Eastern Polynesian populations such as Hawaiʻi and Rapa Nui.
This is particularly important for recessive inherited diseases, which typically develop when a person inherits a disease-causing variant from both parents. If a rare variant becomes more common in a population, the chances of two carriers having children together can also increase. The researchers examined three disease-causing founder variants previously identified in Polynesians and established that they occur at unusually high frequencies in French Polynesia.
One is a variant of ADAMTSL4, a condition where the lens of the eye becomes displaced from its normal position. A second variant affects PDE6B and causes rod-cone retinal dystrophy, an inherited retinal disorder that causes progressive loss of vision. The third involves FAN1 and causes karyomegalic interstitial nephritis, or KMIN, an extremely rare kidney disease that typically progresses to kidney failure.
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