Genetic Defect Found to Cause Adult Dystrophy

Scientists have discovered a genetic abnormality that apparently causes the most common adult form of muscular dystrophy, a discovery that could help research into developing a treatment.

The finding also should allow better diagnosis of the inherited condition, called myotonic dystrophy, prenatally or before symptoms appear in later life, experts said.

Early diagnosis is important because symptoms may not appear until after a person has had children, unwittingly passing along the flawed gene.

Genetic material lies along 23 pairs of string-like structures called chromosomes. This latest work focused on a region of chromosome No. 19. The abnormality is that one segment of genetic material is unusually long. The segment also appeared to be unstable because it lengthened as it passed through successive generations in families, in step with increasing severity of the disease.

Helen Harley of the University of Wales College of Medicine in Cardiff, a co-author of the research, said it is not known how the segment becomes enlarged. But noting that genetic material is made up of building blocks called bases, she said the enlargement probably comes from creation of extra copies of the bases normally in that segment.

Myotonic dystrophy affects about one in every 7,000 to every 8,000 people worldwide. It causes weakness and wasting of voluntary muscles, and often produces difficulty in relaxing muscles, which interferes with movement.

It also can lead to life-threatening irregularities in heartbeat as well as cataracts, mental slowness, premature balding, gastrointestinal complications and sleep disorders.

Although one type of the disease is found in newborns and can kill quickly or cause severe mental retardation, myotonic dystrophy usually shows up in adolescence or early adulthood. It can lead to death in one’s 50s or 60s because of heart or respiratory failure.

The new research is reported in today’s issue of the journal Nature by three international research teams with members in Canada, the Netherlands, Sweden, Britain and the United States.

“This will lead to almost foolproof pre-symptomatic diagnosis or prenatal diagnosis,” more widely applicable than a genetic method used now, commented Dr. Henry Epstein, director of the Jerry Lewis Neuromuscular Disease Research Center at the Baylor College of Medicine in Houston.