A new study reveals that in the US, around 1 in 5,000 boys aged 5-9 years have either Duchenne muscular dystrophy or Becker muscular dystrophy, providing a better understanding of the prevalence of the two disorders.

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Duchenne muscular dystrophy is the most common form of muscular dystrophy. Boys with the condition are often unable to walk by the age of 7-13 years.

The study, led by researchers from the University of Iowa, also found that Hispanic boys are most likely to be affected by the conditions.

The findings are published in the journal Pediatrics.

Muscular dystrophy describes a group of inherited disorders that cause severe muscle weakness, particularly in the lower body, that gets worse over time.

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are the most common forms of the condition, which is much more common in boys. Onset of DMD usually occurs before the age of 5 years, while onset of BMD is most common between the ages of 7-12.

Though the disorders are similar, DMD tends to progress at a more rapid rate, with the majority of boys with the condition being unable to walk by the ages of 7-13 years.

Study co-author Paul Romitti, an epidemiologist in the College of Public Health at the University of Iowa, notes that previous estimates of the prevalence of DMD and BMD in the US have been “crude.”

The Centers for Disease Control and Prevention (CDC), who funded this latest research through the Muscular Dystrophy Surveillance, Tracking and Research Network (MD STARnet) set up in 2010, say most prevalence figures for muscular dystrophy are based on data from other countries, which does not give a true reflection of the number of people affected by the condition in the US.

For their study, Romitti and colleagues assessed the medical records, birth certificates and other data of children born between 1982 and 2011 over six US states: Arizona, Colorado, Georgia, Hawaii, Iowa and western New York.

Using this information, the team calculated the prevalence of DMD and BMD in each state over four 5-year periods: 1991-95, 1996-2000, 2001-05 and 2006-10.

The researchers found that in 1991-95, 1996-2000 and 2001-05, around 2 in every 10,000 – or 1 in 5,000 – boys aged 5-9 years developed DMD or BMD. What is more, the researchers found that Hispanic children were most likely to develop the disorders over these time periods, while African-American children had the lowest risk.

The researchers note that prevalence of DMD and BMD was lower in 2006-10, affecting around 1.5 per 10,000 boys aged 5-9. However, the team says this lower rate may be explained by delayed diagnosis, among other factors.

In addition, the team found that DMD was the most common form of muscular dystrophy in each period, accounting for around three quarters of all cases.

Though DMD and BMD are rare, Romitti says the team’s findings show the conditions are still “an important public health concern.” He adds:

People who have these disorders require daily attention from their families and complex care management from health care providers. The new data will help to estimate the cost for the parents and the health care system. We are continuing to learn more about the total impact of these disorders on the child and the family.”

Last month, Medical News Today reported on a study in which researchers from Duke University in Durham, NC, revealed they had created the first lab-grown contracting human muscle, potentially opening the door to personalized treatment for patients with muscular dystrophy and other muscle-wasting disorders.