DUCHENNE MUSCULAR DYSTROPHY: A Genetic Disease
Patients with Duchenne muscular dystrophy (DMD) have a mutation in the dystrophin gene, which affects their ability to produce full-length, functional dystrophin, a structural protein that connects the cytoskeleton of a muscle fiber to proteins embedded in the cell membrane which in turn are connected to the surrounding extracellular matrix.
DMD is reported to occur in approximately 1 in 3500 live male births.1
Because inheritance of DMD is X-linked recessive, the disease almost exclusively affects boys, who have inherited the disease from their mothers (Figure 1)
but up to 1/3 of cases may be due to spontaneous mutations. Girls can be carriers, with up to 10% of these patients exhibiting some symptoms, but with generally milder presentations.2
The reduction in disease severity in females is attributed to the presence of the second X chromosome carrying a normal dystrophin gene, which compensates for the deficiencies of the defective gene on the first X chromosome.
Figure 1. Inheritance pattern for Duchenne Muscular Dystrophy (DMD). DMD primarily affects male patients, who are likely to have inherited the disease from their mother.
*Approximately 10% of heterozygous females will show disease symptoms.
Genetic testing is the gold standard for diagnosing DMD, and it should be performed for all individuals with clinical signs and symptoms potentially indicative of DMD, as well as for those with a family history of the condition.2
Genetic testing can also make certain patients with DMD eligible for treatments that are currently under investigation.
The Genetic History of Duchenne Muscular Dystrophy
In 1868, French neurologist Guillaume-Benjamin Amand Duchenne described a progressive neuromuscular disorder in 13 children after visiting hospital wards throughout Paris in search of rare neuromuscular disorders. Duchenne observed that the condition ran in families and mainly affected boys, leading him to surmise that the disease was inherited.4
However, beyond being identified as a unique disease entity, little progress was made in understanding Duchenne muscular dystrophy (DMD) until 1986, when the gene for DMD (known as the dystrophin gene) was discovered on the short arm of the X chromosome at position Xp21.4