Researchers have identified the genetic basis of lactose intolerance, the inability of most adults in the world to digest the principal sugar in milk. The finding, published today in the journal Nature Genetics, may lead to the development of a more accurate test for the condition.
Lactose intolerance can cause bloating and indigestion from consuming milk or milk products. More than 30 million Americans, mostly black or Asian, are prone to the condition.
Though lactose intolerance may sound like a disorder, it is in fact natural. In most people the gene for lactase, the enzyme that digests lactose, is switched on at birth and switched off at the age of weaning.
In most Europeans, however, the lactase gene remains active. With the domestication of cattle and goats in the Near East some 10,000 years ago, the ability to digest lactose throughout life could have conferred some nutritional advantage. Biologists speculate that a mutation that prolonged the gene’s activity was suddenly favored and spread throughout the population.
But one finding has baffled biologists: the gene for the lactase enzyme and the gene’s promoter, a neighboring region of DNA that controls the activity of the gene, show no significant difference between populations whose adults can digest lactose and those whose adults cannot