What Is Duchenne Muscular Dystrophy? Expand Duchenne Muscular Dystrophy (DMD) is the most common fatal genetic disease diagnosed in childhood. The disease almost always affect boys, and they tend to be diagnosed before the age of 5. Duchenne Muscular Dystrophy is classified as a rare disease. There are around 2,500 patients in the UK and an estimated 300,000 sufferers worldwide. Children born with Duchenne Muscular Dystrophy have a fault, known as a mutation, on their dystrophin gene, the longest gene in the body. The fault means that they cannot produce dystrophin, a protein that is vital for muscle strength and function. This lack of dystrophin results in a progressive deterioration of muscle strength and function. Duchenne muscular dystrophy is a progressive muscle-wasting disease, which means that symptoms worsen over time. Some parents prefer to read about the stage their child is currently at, while others want to know everything about the different future stages. We have divided up the stages of Duchenne muscular dystrophy here.