Are there different types of MD?

Becker's muscular dystrophy (BMD)

Becker muscular dystrophy (BMD) is a less severe variant of Duchenne muscular dystrophy and is caused by the production of a truncated, but partially functional form of dystrophin.
Survival is usually into middle age.

Congenital muscular dystrophy

Age at onset: birth; symptoms include general muscle weakness and possible joint deformities; disease progresses slowly; shortened life span.

Congenital muscular dystrophy includes several disorders with a range of symptoms. Muscle degeneration may be mild or severe. Problems may be restricted to skeletal muscle, or muscle degeneration may be pair with effects on the brain and other organ systems. A number of the forms of the congenital muscular dystrophies are caused by defects in proteins that are thought to have some relationship to the dystrophin-glycoprotein complex and to the connections between muscle cells and their surrounding cellular structure. Some forms of congenital muscular dystrophy show severe brain malformations, such as lissencephaly and hydrocephalus.

Duchenne muscular dystrophy (DMD)

Duchenne muscular dystrophy (DMD) is the most common childhood form of muscular dystrophy. DMD usually becomes clinically evident when a child begins walking. Patients typically require a wheelchair by age 10 to 12 and die in their late teens or early 20s.

In the early 1990s, researchers identified the gene for the protein dystrophin which, when absent, causes DMD. The dystrophin gene is the largest known gene in humans. Since the gene is on the X-chromosome, this disorder affects primarily males. Females who are carriers have milder symptoms. Sporadic mutations in this gene occur frequently, accounting for a third of cases. The remianing two-thirds of cases are inherited in a recessive pattern. age at onset: two to six years; symptoms include general muscle weakness and wasting; affects pelvis, upper arms, and upper legs; eventually involves all voluntary muscles; survival beyond 20s is rare.

However recent advances in medical care has caused the survival age to increase significantly.

Distal muscular dystrophy

Distal muscular dystrophies' age at onset: 40 to 60 years; symptoms include weakness and wasting of muscles of the hands, forearms, and lower legs; progress is slow; rarely leads to total incapacity.

Miyoshi myopathy, one of the distal muscular dystrophies, causes initial weakness in the calf muscles, and is caused by defects in the same gene responsible for one form of LGMD.

Emery-Dreifuss muscular dystrophy

Age at onset, childhood to early teens. Symptoms include weakness and wasting of shoulder, upper arm, and shin muscles; joint deformities are common; progress is slow; sudden death may occur from cardiac problems.

Facioscapulohumeral muscular dystrophy (FSHD)

FSHD initially affects muscles of the face, shoulders, and upper arms with progressive weakness. Symptoms usually develop in the teenage years. Some affected individuals become severely disabled. The pattern of inheritance is autosomal dominant, but the underlying genetic defect is poorly understood. Most cases are associated with a deletion near the end of chromosome 4.

Limb-girdle muscular dystrophy (LGMD)

LGMD's all show a similar distribution of muscle weakness, affecting both upper arms and legs. Many forms of LGMD have been identified, showing different patterns of inheritance (autosomal recessive vs. autosomal dominant). In an autosomal recessive pattern of inheritance, an individual receives two copies of the defective gene, one from each parent. The recessive LGMDs are more frequent than the dominant forms, and usually have childhood or teenage onset. The dominant LGMDs usually show adult onset. Some of the recessive forms have been associated with defects in proteins that make up the dystrophin-glycoprotein complex.

Death from LGMD is usually due to cardiopulmonary complications.

Myotonic muscular dystrophy

Myotonic MD's age at onset: 20 to 40 years.

Myotonic muscular dystrophy is the most common adult form of muscular dystrophy. It is marked by myotonia as well as muscle wasting and weakness. Myotonic dystrophy varies in severity and manifestations and affects many body systems in addition to skeletal muscles, including the heart, endocrine organs, eyes, and gastrointestinal tract. Myotonic dystrophy follows an autosomal dominant pattern of inheritance. Myotonic dystrophy results from the expansion of a short repeat in the DNA sequence (CTG in one gene or CCTG in another gene). In other words, the the gene defect is an abnormally long repetition of a three- or four-letter "word" in the genetic code. While the exact mechanism of action is not known, this molecular change may interfere with the production of important muscle proteins.

Oculopharyngeal muscular dystrophy

Oculopharyngeal MD's age at onset: 40 to 70 years; symptoms affect muscles of eyelids, face, and throat followed by pelvic and shoulder muscle weakness, has been attributed to a short repeat expansion in a gene which regulates the translation of the genetic code into functional proteins.