Identifying a new disease mechanism, geneticists have found that the reawakening of a gene in a stretch of seemingly useless, or junk, DNA causes a common form of muscular dystrophy.
It is almost certain, specialists say, that other diseases will be found to have similar causes. The discovery also points the way, they say, toward new research on treatment of this disease.
The human genome is riddled with so-called dead genes that have not been active for ages, part of a vast amount of the genome that has no known function. But this is the first time, geneticists say, that they have seen a dead gene come back to life and cause a disease.
The disease, facioscapulohumeral muscular dystrophy, or FSHD, was known to be inherited in a simple pattern. But before this research, reported online yesterday in Science by an international group of researchers, its cause was poorly understood.
The culprit gene is part of what has been called junk DNA, regions whose function, if any, is largely unknown. In this case, the gene had seemed permanently disabled.
FSHD affects about 1 in 20,000 people, causing a progressive weakening of muscles in the upper arms, around the shoulder blades, and in the face — people who have the disease cannot smile. It is a dominant genetic disease. If a parent has the gene mutation that causes it, each child has a 50 percent chance of getting it, too. And anyone who inherits the gene is certain to get the disease.
About two decades ago, geneticists zeroed in on the region of the genome that seemed to be the offender: the tip of the longer arm of chromosome 4, which was made up of a chain of repeated copies of a dead gene. The dead gene was also repeated on chromosome 10, but that area of repeats seemed innocuous, unrelated to the disease. Only chromosome 4 was a problem.
The more they looked at that region of chromosome 4, the more puzzling it was. No one whose dead gene was repeated more than 10 times ever got FSHD.
Researchers say those extra copies change the chromosome’s structure, shutting off the region.
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