Each year, the parents of an estimated one in 20,000 newborns are shocked to learn their child has type 1 congenital myotonic dystrophy (CDM1), a progressive and crippling genetic disorder.
Although doctors know that babies inherit CDM1 from their mother and prenatal tests are available, many children are not diagnosed until they are born.
“In these instances, mothers don't know that they have type 1 myotonic dystrophy (DM1) – a common form of muscular dystrophy – because they have mild symptoms or none at all,” notes Mani S. Mahadevan, M.D. a pathologist at the University of Virginia Health System and winner of the 2007 Rachel Fund Award for myotonic dystrophy (DM) research.
DM1 is the nation's most prevalent inherited neuromuscular disorder, afflicting men and women equally. In general, parents with DM1 pass it along to half of their children. Affected sons and daughters usually begin exhibiting symptoms in their teens or twenties. Although symptoms tend to get more severe and appear earlier in life with each successive generation, some people inherit such a mild form of the disease that it goes unnoticed.
CDM1 is by far the severest form of DM. Because they lack muscle tone, afflicted newborns are floppy like rag dolls. Typically, they suffer from poor sucking and swallowing responses, respiratory ailments and impaired motor development. Twenty-five percent of them die within a month. The outlook for those who survive is bleak – they become increasingly weak and disabled and suffer from mental retardation.
Children with CDM1 face a lifetime of physical and occupational therapy and require special educational programs. Currently, there is no treatment that either slows down or cures this disorder.
Changing this prognosis is a goal of Dr. Mahadevan. Over the next two years, the Rachel Fund will be providing $239,756 (Canadian) for his research. In a groundbreaking study published last year, Dr. Mahadevan and his UVa colleagues discovered how to activate and deactivate DM1 in laboratory mice. Now, their goal is to translate what they have learned to benefit humans.
Dr. Mahadevan has been on the leading edge of DM research for more than a decade. In 1992, as a member of a Canadian research group, he helped discover the genetic mutation that causes DM1.
The mutation occurs when a gene called myotonic dystrophy protein kinase (DMPK) makes extra copies of nucleotide sequence consisting of cytosine, thymine and guanine (CTG). In normal individuals, the DMPK gene has between five and 30 copies of the CTG sequence. People with DM1 have 50 to several thousand copies. Babies with CDM1 have more than 1000 of them.
The Canadian team discovered that everyone with DM1 has the CTG mutation on chromosome 19, and this discovery led to the development of a simple gene-based diagnostic test for the disease. The test is now used around the world.
Today, scientists are trying to understand how extra CTG repeats cause DM. At UVa, Dr. Mahadevan has taken this research to the next level. To prove the theory that DM is caused by toxic RNA (ribonucleic acid), his team created a new kind of mouse model. It attached many added CTG repeats to the DNA of a gene that made the muscles in mice glow green under a microscope. This enabled easy observation of what occurred as the DNA converted into RNA and, subsequently, into the proteins that determine the function of the body's cells.