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.
The muscle weakness is not noticeable at birth, even though the child is born with the gene which causes it. The weakness develops gradually. It usually shows up in early childhood. Symptoms are mild at first, but increase as the child gets older.
The name Duchenne comes from the doctor who first studied this condition.
How common is Duchenne muscular dystrophy?
About 1 in 3,500 boys in the UK are born with DMD. There are other types of muscular dystrophy too, which are rarer. See separate leaflet called Muscular Dystrophies - An Overview for more detail about other types of muscular dystrophy.
The U.S. Centers for Disease Control funded the work, through the Muscular Dystrophy Surveillance, Research and Tracking Network, or MD STARnet.
The team found the disorders in roughly 2 per 10,000 boys in the 1991-1995, 1996-2000 and 2001-2005 periods. In 2006-2010, the prevalence was 1.5, but the researchers believe the lower figure could be due to delayed diagnosis, among other factors.
What are the symptoms of Duchenne muscular dystrophy?
The symptoms usually appear before age 6 and may appear as early as infancy. Typically, the first noticeable symptom is delay of motor milestones, including sitting and standing independently. The mean age for walking in boys with Duchenne muscular dystrophy is 18 months. There is progressive muscle weakness of the legs and pelvic muscles, which is associated with a loss of muscle mass (wasting). This muscle weakness causes a waddling gait and difficulty climbing stairs. Muscle weakness also occurs in the arms, neck, and other areas, but not as severely or as early as in the lower half of the body.
Calf muscles initially enlarge and the enlarged muscle tissue is eventually replaced with fat and connective tissue (pseudohypertrophy). Muscle contractures occur in the legs, making the muscles unusable because the muscle fibers shorten and fibrosis occurs in connective tissue. Occasionally, there can be pain in the calves.
Symptoms usually appear in boys aged 1 to 6. There is a steady decline in muscle strength between the ages of 6 and 11 years. By age 10, braces may be required for walking, and by age 12, most boys are confined to a wheelchair. Bones develop abnormally, causing skeletal deformities of the spine and other areas.
Muscular weakness and skeletal deformities frequently contribute to breathing disorders. Cardiomyopathy (enlarged heart) occurs in almost all cases, beginning in the early teens in some, and in all after the age of 18 years. Intellectual impairment may occur, but it is not inevitable and does not worsen as the disorder progresses.
Few individuals with DMD live beyond their 30s. Breathing complications and cardiomyopathy are common causes of death.
Hispanic youth had a higher prevalence in all but the last time period, while African-American children were least likely to be affected for all time periods.
Three-quarters of the 845 total cases were Duchenne, according to the study.
The frequency across the time periods is roughly the same as found in a MD STARnet study, in four states and reported in 2007, and from a study done in Colorado in 1974, according to the paper.
Becker muscular dystrophy
Becker muscular dystrophy is a genetic condition that causes your muscles to become damaged and weakened over time, resulting in loss of muscle tissue. If you have this condition, you could begin to experience problems walking around age 16. Becker muscular dystrophy usually affects boys, with symptoms appearing between age 5 and 15. There is more than one type of muscular dystrophy, and Becker is similar to another type known as Duchenne. Becker is less severe and less common.
What Causes Becker Muscular Dystrophy?
The condition is caused by abnormality of the gene that is responsible for making a protein called dystrophin. Dystrophin helps keep muscle cells intact; without it, your muscles cannot contract properly. You may inherit the abnormal dystrophin gene, or it may appear spontaneously.
Who Is at Risk for Becker Muscular Dystrophy?
The disease almost always affects males though it can occur in females. You are at a higher risk if you have relatives with the condition.
Despite their rarity, the researchers say medical professionals should be prepared.
“People who have these disorders require daily attention from their families and complex-care management from health-care providers,” says Romitti, professor in the UI College of Public Health. “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.”
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Contributing authors include: Yong Zhu, former post-doctoral researcher at the UI; Soman Puzhankara, with the UI College of Public Health; Katherine James, at the University of Colorado-Aurora; Sarah Nabukera, former post-doctoral researcher at the UI; Gideon Zamba, associate professor in biostatistics at the UI; Emma Ciafaloni, at the University of Rochester; Christopher Cunniff, at the University of Arizona; Charlotte Druschel, at the New York State Department of Health and State University of New York system; Katherine Mathews, pediatrics professor at the UI; Dennis Matthews, University of Colorado-Aurora; John Meaney, University of Arizona; Jennifer Andrews, University of Arizona; Kristin Caspers Conway, associate research scientist at the UI; Deborah Fox, New York State Department of Health; Natalie Street, Melissa Adams and Julie Bolen at the Centers for Disease Control and Prevention.
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Richard Lewis
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319-384-0012
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University of Iowa
Journal -
Pediatrics