Download Case #1. Huntington`s disease in Barranquitas, Venezuela. Your

Case #1. Huntington’s disease in Barranquitas, Venezuela.
Your team is sent to Barranquitas, Venezuela to investigate reports of greatly elevated incidences of
Huntington’s disease in this town. Huntington’s causes loss of muscle function which, among other
symptoms, causes the sufferer to have problems swallowing. Patients often die of choking or from
malnutrition. This disease typically affects 1 in 10,000 people worldwide, but in Barranquitas roughly 1
in 10 people are afflicted. Your job is to provide insight as to why the disease is so prevalent in
Barranquitas, and why it persists despite being such a debilitating disease.
Your investigation:
a. You look up Huntington’s on Wikipedia(!): “It is much more common in people of Western European
descent than in those of Asian or African ancestry. Physical symptoms of Huntington's disease can begin
at any age from infancy to old age, but usually begin between
35 and 44 years of age.”
b. You are able to assemble a family pedigree (right), showing
which members of a single family had Huntington’s.
c. You discover that Barranquitas was founded in 1760 by a
group of 21 Spanish colonists, and that the population has
expanded to 9,000. Most residents are direct descendants of
village founders.
d. In the past 80 years, improvements in sanitation and the
importation of anti-malarial drugs have led to an increase in life-expectancy from 34 to a new high of 63
(there is a similar trend in neighboring towns not so affected by Huntington’s).
e. You find that an allele at a particular locus is found in all residents suffering from Huntington’s, and
only in non-sufferers who are younger than 33 years old. You develop a simple genetic screen for this
allele so that you can sample blood from a person and determine whether they have this gene or not.
In your report, you are asked to address the following:
1) Is this genetic disease probably caused by a dominant or recessive allele? How do you know?
2) What evolutionary process (natural selection, genetic drift, sexual selection, etc.) has led to
Barranquitas having such a high incidence of Huntington’s?
3) This is a disease that kills people, but nevertheless persists in the population. What feature of this
disease allows it to persist? Why has it only recently become problematic in Barranquitas?
4) Suggest some strategies for remediation of Huntington’s in Barranquitas (at least 2)
5) What are the risks / problems involved with each strategy?