Deck 1: What Is in a Human Genome

Question 1

Leishmaniasis is an infection that humans contract from sandflies that transmit the microorganism Leishmania braziliensis. The first sign is a skin lesion, followed by facial disfiguration. The disease is endemic (very common) in Bolivia, where it is seen more in males, younger people, and those who spend the most time in the forest. A genetic susceptibility might also influence who becomes infected, as suggested by highly susceptible strains of mice. What type of evidence in the Bolivian population, which consists of indigenous and immigrant populations, might suggest an inherited component to susceptibility of this infection?

Answer 1

An inherited susceptibility to leishmaniasis might be involved if blood relatives who are separated geographically become sick more often than people who only have in common where they live.

Question 2

Osteoporosis thins bones in millions of people. A much rarer, inherited condition, osteopetrosis, acts oppositely, increasing bone mass. Osteopetrosis does not affect health, and is typically discovered on x-rays. Why might studying how osteopetrosis arises be useful, even though it doesn't cause symptoms?

Answer 2

Studying osteopetrosis can reveal how healthy bone mass is maintained, which might provide insights into osteoporosis, which has an opposite phenotype and is more common.

Question 3

In acute intermittent porphyria, an environmental factor such as abuse of drugs or alcohol or fasting triggers potentially fatal attacks on the nervous system. An abnormal enzyme causes the condition. Why is this disorder considered genetic if it only produces symptoms in the presence of a specific environmental trigger?

Answer 3

The condition is inherited because presence of a particular genetic variant is necessary for symptoms to occur.

Question 4

Although seizures are usually not inherited, benign infantile familial convulsions run in families. How can studying this inherited illness provide information that may help people with non-inherited seizures?

Question 5

Due to inherited differences in the way the body processes cholesterol, some people can eat a fatty diet yet have healthy blood serum cholesterol, and others develop dangerously high cholesterol levels if they do not eat wisely. Several drugs can lower blood serum cholesterol level. Researchers found that people with a certain variant of a gene encoding a protein that transports cholesterol into liver cells (cholesteryl ester transfer protein, or CETP) are likely to have a cholesterol problem, and are also more likely to benefit from cholesterol-lowering drugs than people with different alleles. What information would be important to have before undergoing a CETP gene test and possibly taking a cholesterol-lowering drug?

Question 6

In Graves disease, the immune system attacks the thyroid gland, which normally produces hormones controlling energy utilization. Siblings of people with Graves disease are 15 times as likely to develop the disorder as people whose siblings are unaffected. Women develop the condition more often than men, and a high percentage of affected individuals smoke. Do you think that Graves disease is caused solely by an abnormal gene, solely by an environmental trigger, or might there be another explanation?