NEW YORK (AP) _ Scientists have apparently identified a genetic cause of lactose intolerance, which affects 30 million to 50 million Americans. The work may lead to a simple diagnostic blood test.
People with the condition can't digest significant amounts of lactose, the main sugar of milk. So soon after they eat or drink dairy products, they can feel nausea, cramps, bloating, gas and diarrhea. The condition is usually managed by avoiding or limiting the offending foods.
While there are several causes of lactose intolerance, it mostly commonly appears when people lose the ability to make enough of the enzyme lactase, which breaks down lactose. The study focused on this form of the condition.
Scientists already knew that the lactase gene itself wasn't responsible. The new work implicates a slight variation in the DNA code, called a variant, that lies elsewhere on the same chromosome.
The work, published online by the journal Nature Genetics, was done by Dr. Leena Peltonen of the University of California, Los Angeles, with colleagues in Finland.
In tests of nine Finnish families and 236 people of other ethnic backgrounds, they found the DNA variant reliably appeared in people with the condition, but not in other people.
It's not clear how this variant promotes the condition, Peltonen said. The work indicates people must inherit it from both parents to become lactose intolerant.
If the finding holds up in further work with large numbers of people of different ethnic backgrounds, it could become the basis of a simple blood test for diagnosis, she said.
Current tests are more cumbersome and time-consuming.
Dallas Swallow, a University College London researcher who has studied the genetics of lactose intolerance, said it will take more work to prove that the variant causes the condition, but that it probably does. ``I think it looks quite good,'' she said.
Swallow said there may also be other genetic causes as well.