Researchers report new figures on 2 muscular dystrophy disorders

Researchers in public health have reported in the first broad study in the United States the frequency of two muscle-weakness disorders that strike mostly boys: Duchenne muscular dystrophy and Becker muscular dystrophy.

The research team, led by the University of Iowa, found that about 1 in 5,000 boys, between 5 and 9 years old, have the inherited disorders. They also find the diseases appear to affect Hispanic boys more often than white or African-American boys, for reasons that are not well understood.

The findings are important, because they give a better understanding of the number of children and families affected by the disorders. They also give doctors and health-care professionals valuable information, so they can better plan to care for those affected, especially as the diseases progress.

"There were always some rather crude estimates of how common these muscular dystrophies are," says Paul Romitti, an epidemiologist at the UI and corresponding author of the study, published online in the journal Pediatrics. "It tells us that they're still an important public health concern."

Muscular dystrophies are a group of genetic disorders that result in muscle weakness over time. The most common muscular dystrophy in children is Duchenne muscular dystrophy, which predominantly affects males. Historically, Duchenne has resulted in loss of walking ability between ages 7 and 13 years, and death in the teens or 20s. Becker muscular dystrophy is similar to Duchenne, but has later onset and slower, more variable progression of symptoms. There is no cure for either disorder.

In the population-based study, researchers analyzed data - culled mostly from birth and death certificates and medical records - for children born between 1982 and 2011 in six states: Arizona, Colorado, Georgia, Hawaii, Iowa and western New York. They calculated the disorders' prevalence across four five-year time periods, beginning in the 1991-1995 period and ending in 2006-2010.

Duchenne muscular dystrophy is a condition which causes muscle weakness. It starts in childhood and may be noticed when a child has difficulty standing up, climbing or running. It is a genetic condition and can be inherited. It usually affects only boys, although girls may carry the Duchenne gene. Boys with Duchenne muscular dystrophy should have regular check-ups and physiotherapy from childhood, and are likely to need increasing help and treatments from about the age of nine years.

What is Duchenne muscular dystrophy?

Duchenne muscular dystrophy (DMD) is an inherited (genetic) condition which affects the muscles, causing muscle weakness. It is a serious condition which starts in early childhood. The muscle weakness is mainly in the 'proximal' muscles, which are those near the trunk of the body, around the hips and the shoulders. This means that fine movements, such as those using the hands and fingers, are less affected than movements like walking.