It makes sense that faulty genes can cause deafness, but now researchers have discovered a gene that prevents people from losing their hearing. Like a colonel pulling rank on a lieutenant, the second gene presumably overrules the orders of the deafening gene, allowing the ear to develop normally. Understanding this new gene might eventually lead to new treatments for protecting people's hearing.
Thirty genes that cause childhood deafness have already been found, many through studies of extended families with several deaf members. Looking for another deafness gene, a team of American and Pakistani scientists has been following one such family with 141 members and several marriages between first cousins. Geneticists prize such marriages, which are common in Pakistan, for their ability to unmask rare recessive genes. A recessive gene remains hidden when a carrier marries someone who lacks it.
Hoping to pinpoint the location of the family's deafness gene, researchers led by molecular geneticist Edward Wilcox of the National Institute on Deafness and Other Communication Disorders in Bethesda, Maryland, pored over the chromosomes of deaf and hearing family members. All eight deaf people shared a short stretch of DNA on chromosome 4, suggesting that the gene responsible for their deafness lies nearby.
This straightforward story took an odd twist when the researchers discovered that seven family members with normal hearing also carried this stretch of DNA. The researchers were puzzled. Maybe chromosome 4 wasn't the site of the deafness gene after all. Or perhaps another gene was modifying the effect of the deafness gene. The second alternative proved correct: Another chromosomal hunt turned up a sequence on chromosome 1 that was present in the seven hearing kin, but absent in their deaf relatives, the researchers report in the December issue of Nature Genetics.
"The really exciting thing about this paper is the modifier [gene]," says Linda Call, a molecular geneticist at Harvard University. Other genes that alleviate diseases have been described, but this is the first one found in humans that prevents deafness. The finding fine-tunes our understanding of how the ear works, she says, and might someday inspire therapies that protect against deafness.