• Huntington’s Chorea

Huntington’s Chorea: Evolution and Genetic Disease (1 of 3)

Huntington’s chorea is a devastating human genetic disease. A close look at its genetic origins and evolutionary history explains its persistence and points to a potential solution to this population-level problem.

People who inherit this genetic disease have an abnormal dominant allele that disrupts the function of their nerve cells, slowly eroding their control over their bodies and minds and ultimately leading to death. In the fishing villages located near Lake Maracaibo in Venezuela (see map at left), there are more people with Huntington’s disease than anywhere else in the world. In some villages, more than half the people may develop the disease.¹

How is it possible that such a devastating genetic disease is so common in some populations? Shouldn’t natural selection remove genetic defects from human populations? Research on the evolutionary genetics of this disease suggests that there are two main reasons for the persistence of Huntington’s in human populations: mutation coupled with weak selection.

The diagram at right shows how the Huntington’s allele is passed down. Since it is the dominant allele, individuals with just one parent with Huntingtons’s chorea have a 50-50 chance of developing the disease themselves.

The people of Lake Maracaibo.

• Photo of Venezuelan familiy © 1983 by Steve Uzzell
¹A Tale of Pain and Hope on Lake Maracaibo (int’l edition), Business Week Online. May 29, 2000.