Humans are Harder than Mice
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Marci Lesperance
Photo: Lin Jones |
Scientists like Marci Lesperance, M.D., associate professor of pediatric otolaryngology in the Medical School, can only dream of having DNA from an extended family of 600 people, the number of mice Richard Miller and David Burke work with in trying to identify genes that control age-related hearing loss. As someone who studies inherited deafness in humans, Lesperance is lucky to get DNA from 10 members of the same family.
Especially in the United States, Lesperance says people don’t have as many babies as they used to, extended families don’t live near each other, and no one stays in one place anymore.
“The U.S. population is so mobile, it can be hard to track everyone down to recruit them for a research study,” she says. “Many times people don’t even know everyone in their extended family. That’s why many researchers go overseas — it’s just much harder to collect data on U.S. populations.”
This is especially true for studies of rare recessive genetic mutations that cause deafness, if the mutation is inherited from both mother and father. In this case, researchers often recruit study subjects in countries where people tend to marry close relatives and families remain in the same village for generations.
Glenn Green also studies human deafness, but he doesn’t have to travel far to find potential research subjects. He focuses on connexin 26 mutations, the most common genetic cause of deafness in humans. Mutations in the GJB2 gene — which stores the genetic code for connexin 26 protein — are responsible for half of all cases of recessive inherited deafness in children. Researchers estimate that one of every 31 people carries one of 50 known mutations in connexin 26.
“The carrier frequency for connexin 26 mutations is comparable to the carrier frequency for the mutation that causes cystic fibrosis,” Green says. “These mutations occurred thousands of years ago and have been passed on for generations.”
Since connexin 26 mutations are so widespread and age-related hearing loss is so common, could there be a connection? That’s one of the questions Green and Margaret Lomax hope to answer in future research.
Green and Lomax want to look for genetic differences between two groups of people in genes known to be associated with hearing loss. The first group will include adults who developed profound deafness early in life and the second will be people in their 80s with near normal hearing. By comparing the two groups, they and other U-M scientists hope to find variations in DNA that could predispose people to age-related or noise-related hearing loss.
—Sally Pobojewski
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