Huntington's Disease Is Caused by a Single Dominant Allele and Results

Huntington's disease is caused by a single dominant allele and results in progressive mental and neurological damage. The disease usually becomes symptomatic when a person is between 30 and 50 years old and the patient usually dies within 15 years of diagnosis. Approximately 1 in 25,000 Caucasians have this disease. Huntington's disease has not been associated with any other disease, now or in the past. Why might natural selection not have eliminated such a deleterious allele from the population?

A) Natural selection acts through reproduction, and most individuals with Huntington's disease reproduce prior to discovery.
B) Diseases tend to remain in populations because of heterozygous carriers.
C) Modern health care has acted as an agent against selection.
D) Natural selection tends not to work on human diseases and in human populations.
E) Natural selection only works on young individuals or newborns. Huntington's disease only works on older people.