The Major Forms of Muscular Dystrophy

Duchenne’s MD This form is one of the most common and debilitating forms. It results from an abnormal gene on the X chromosome that encodes for a muscle protein named dystrophin. In this regard, typically a female is a “carrier” of the disorder as women have two X chromosomes. This allows an affected X chromosome to be hidden by the normal one. In a male however, because he has only one X chromosome and one Y chromosome, an affected X chromosome will result in the clinical disease. Therefore, Duchenne’s MD only affects male individuals. The lack of normal dystrophin results in symptoms usually developing between the ages of 2 to 6. Muscular symptoms include progressive weakness, loss of muscle size, and hardening of muscle tissues. Also as time evolves, other tissues are involved including the heart muscle and sometimes brain tissue resulting in mild retardation. Muscle weakness results in spinal deformities, and this mechanically affects respiratory function. Most patients require wheelchair ambulation by the age of 12, and longevity of life is limited to late teenage years to early 20’s. Becker’s MD This form is similar to Duchenne’s MD but is milder. It also involves the X chromosome, so again only male individuals are affected. Onset of symptoms can develop anywhere from the age of 2 to adolescence, and progression is slower. Most patients can walk into their 30’s and longevity, though limited, usually extends into mid-life or more. The heart muscle can also be involved in this disorder.

Facioscapulohumeral MD
This form of Muscular Dystrophy affects both male and female patients, with onset usually ranging from late childhood to early adulthood. As its name describes, it affects muscles of the face, shoulders and upper arms. This results in upper body weakness and problems chewing, talking, and swallowing primarily, but walking can also be affected. Lifespan is usually normal, but disability varies greatly.

Limb-Girdle MD
Again both male and female patients are affected with this variant, but walking is almost always affected eventually resulting in marked difficulty within 20 years of onset. Onset typically is also late childhood to early adulthood, but longevity of life is usually abbreviated to mid the late adulthood. Muscles affected in this Limb-Girdle MD are those around the hips and shoulders.

Myotonic Dystrophy
Myotonia refers for an abnormal ability for a muscle to relax after contraction, which is a hallmark of this form of MD. Myotonic Dystrophy is the most common form in adults, and it affects women and men equally. It is due to an abnormal gene on Chromosome 19, and onset is usually between early childhood through adulthood. Distribution of muscle weakness is typically in the hands, face, and feet initially, progressing to other areas in a general fashion later. In addition, cardiac muscle can be affected, and other common features can include baldness, cataracts, memory loss and hormonal changes. Lifespan is usually diminished though patients can remain functional for a long time with this disease.

Distal MD
As its name would suggest, this form involves muscles of the hands and feet mostly which are the most distant from the body’s center. Forearms and lower legs can be affected as well, but this rare disorder progresses very slowly. It affects both men and women, but disability is usually much milder than with other forms, and it is not very common in occurrence. Onset is usually in mid to late life.

Oculopharyngeal MD
This form also affects both men and women in mid to late life. It affects the muscles of the eyes and throat, with swallowing difficulty being the most symptomatic problem. Shoulder and hip weakness can develop later, but overall it progresses very slowly.

Emery-Dreifuss MD
Developing usually in childhood to late teenage years, this form usually affects the calf muscles and muscles of the upper arms and shoulders. It is likely an X chromosome disorder as it only affects males. The most concerning feature is its involvement of heart muscle fibers which lead to life-threatening heart rhythm disturbances. This can even occur in women who are “carriers” of the gene abnormality but have no overt evidence of disease otherwise. Overall this is much slower in progression and severity, and is relatively rare.

Congenital MD
Though rare, this condition is present from birth and involves generalized muscle function. Infants are usually weak all over with floppy muscle tone and joint deformities. In one form, a key muscle protein filament called myosin is absent, and in another (Fukuyama variant) there is associated mental retardation and sometimes seizures. Both male and female infants are affected equally.