Posted on 01/15/2002 9:48:32 PM PST by jennyp
UCLA and Finnish researchers have identified a genetic mutation for lactose intolerance, a painful digestive condition that afflicts some 30 million to 50 million North Americans, 75 percent of African Americans and 90 percent of Asian Americans. The findings are reported in the Jan. 14 issue of Nature Genetics.
Dr. Leena Peltonen, UCLA's Gordon and Virginia MacDonald Distinguished Chair in Human Genetics, and her associates at the UCLA School of Medicine, collaborated with colleagues at Finland's National Public Health Institute to identify a DNA variant outside of the gene associated with lactose intolerance.
Lactose intolerance occurs in children after weaning, when the cells that line the small intestine decrease their production of an enzyme called lactase-phlorizin. For years, scientists' analyses of the human gene that encodes this enzyme revealed no mutation associated with the disorder. As a result, Peltonen's team looked for a DNA variant outside of the encoding gene.
The researchers drew blood samples in order to study the DNA of a Finnish group of 196 lactose-intolerant adults of African, Asian and European descent. Each of them showed the genetic mutation for lactose intolerance in their DNA.
"That we found the same DNA variant in all lactose-intolerant people across distant ethnic groups indicates to us that it is very old," Peltonen said. "We believe that the variant we identified in patients is the original form of the gene — which mutated to tolerate milk products when early humans adopted dairy farming.
"This suggests that everyone was originally lactose intolerant," she added. "It's an excellent example of a useful mutation in human history."
Lactose intolerance is the inability to digest large amounts of lactose — the main sugar found in dairy products. Symptoms include nausea, cramps, bloating, gas and diarrhea, which begin about 30 minutes to 2 hours after consuming foods containing lactose.
Current tests for lactose intolerance are unreliable or tedious. Peltonen and her colleagues' findings will help speed the development of non-invasive, reliable diagnostic tests and better treatment for this common problem.
Ha! I'm more evolved than you are!
Us radio astronomers have to be quick! LOL!!
ROTFLMAO!! So I guess I am further down on the evolutionary ladder?
"This suggests that everyone was originally lactose intolerant," she added. "It's an excellent example of a useful mutation in human history."
Yes, way down. I, on the other hand, guzzle milk all the time. The future belongs to me!
This article is bunk. Consider the first human who was not lactose intolerant. What woman would have this mutated freak? Who would he mate with? A feral chicken???
...a damned dark day for Exlax, though.
So how did we invent dairy farming if we were all lactose-intolerant? Hmmmm? </luddite mode>
Which came first the herd or the or the non-curd? And why?
You might consider this. Lactose intolerance and the breastfed baby
Lactose is the sugar in all mammalian milks. It is produced in the breast and is independent of the mother's consumption of lactose. It is present in a constant concentration in breastmilk.
Primary (or true) lactose intolerance is an extremely rare genetic condition and is incompatible with normal life without medical intervention. A truly lactose intolerant baby would fail to thrive from birth (ie not even start to gain weight), and show obvious symptoms of malabsorption and dehydration - a medical emergency case needing a special diet from soon after birth.
Anything that damages the gut lining, even subtly, can cause secondary lactose intolerance. The enzyme lactase is produced in the very tips of folds of the intestine, and anything that causes damage to the gut may wipe off these tips and reduce the enzyme production, for example.
And yes, you are correct that there are other conditions, e.g. intestinal inflammation, etc. which can reduce the presence of this enzyme, causing temporary or permanent lactose intolerance. But the point is that the normal presence of the enzyme into adulthood is an adaptive mutation. Diseases or conditions which can strip this advantage are interesting but beside the point.
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