DUCHENNE MUSCULAR DYSTROPHY



Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy

Introduction

Duchenne muscular dystrophy is a rapidly progressive form of muscular dystrophy. It is caused by a defective gene, but it often occurs in people from families without a known family history of the condition. Duchenne muscular dystrophy is inherited in an X-linked recessive pattern. Because women have two X chromosomes, if one contains a normal copy of the gene, that gene will make enough of the protein to prevent symptoms. But boys have an X chromosome from their mother and a Y from father, so if the X chromosome is defective, there is no second X to make up for it and they will develop the disease. It is marked by progressive loss of muscle function, which begins in the lower limbs. The cause of the muscle impairment is an abnormal gene for dystrophin (a protein in the muscles).

Duchenne's muscular dystrophy is an inherited disease of skeletal (voluntary) muscles and the most common form of childhood muscular dystrophy. It generally appears from age three to six years and worsens rapidly. At first, muscle weakness and wasting (atrophy) within the pelvic (hipbone) area occurs followed by similar problems in the shoulder muscles. Eventually, muscle weakness and atrophy affect the trunk and forearms and gradually spread to the major muscles of the body. From 20 to 30 boys of every 100,000 born are affected by Duchenne's muscular dystrophy. The sons of carrier females (women with one defective chromosome but no symptoms themselves) each have a 50% chance of having the disease, and the daughters each have a 50% chance of being carriers.

Comparison of Duchenne muscular dystrophy with Facioscapulohumeral muscular dystrophy

FSH is a muscle wasting condition, caused by a genetic fault, which may be affecting the regulation of the level of many of the different proteins in muscles.

The name describes the usual distribution of weakened muscles: 'facio'=facial; 'scapulo'=shoulder blade; 'humeral'= upper arm. Landouzy-Dejerine and facioscapuloperoneal muscular dystrophy are two previously used terms. Also, some people with a diagnosis of scapulohumeral or scapuloperoneal syndromes may have this condition. However, the legs can also be affected.

It is probably the third most common muscular dystrophy (after Duchenne and myotonic dystrophies), although its frequency may vary in different places and quite possibly in different racial groups. Estimates of frequency have varied from one in about 400,000 to one in 20,000. In Britain, the frequency is at least one person in every 50,000, and probably closer to one in 20,000, accounting for between about 1200 and 3000 cases in all.

It is a genetic condition, present from when or soon after egg and sperm come together at conception. Normally, at a particular site on the gene map, each of us has many copies of a particular sequence of genetic instruction (DNA), arranged like a train of identical carriages. FSHD is caused when the number of copies is reduced below a certain level, like a train having too few carriages. In some way this seems to influence the production or assembly of several of ...