Other Muscular Dystrophies

Several much less common forms of muscular dystrophy, all inherited, also cause progressive muscle weakness.

Facioscapulohumeral (Landouzy-Dejerine) muscular dystrophy is transmitted by an autosomal dominant gene; therefore, a single abnormal gene is sufficient to cause the disorder, and the disorder can appear in either males or females. Symptoms usually begin between the ages of 7 and 20. The facial and shoulder muscles are always affected, so that a child has difficulty whistling, closing the eyes tightly, or raising the arms. Some people with the disease also develop a footdrop (the foot flops down). The weakness is rarely severe, and people who have Landouzy-Dejerine muscular dystrophy have a normal life expectancy.

Limb-girdle muscular dystrophies cause weakness in the muscles of either the pelvis (Leyden-Möbius muscular dystrophy) or the shoulder (Erb's muscular dystrophy). These inherited disorders usually do not appear until adulthood and rarely produce serious weakness.

Mitochondrial myopathies are muscle disorders inherited through faulty genes in mitochondria (the energy factories of cells; they carry their own genes). Because sperm do not contribute mitochondria during fertilization, all mitochondrial genes come from the mother (see Section 1, Chapter 2). Therefore, although they are equally likely in males and females, these disorders can never be inherited from the father. These rare disorders sometimes cause increasing weakness in one or a few muscle groups, such as the eye muscles (ophthalmoplegia). One mitochondrial myopathy is called the Kearns-Sayre syndrome.

Diagnosis and Treatment

Diagnosis requires taking a sample of the weak muscle tissue for biopsy and either examining it under a microscope or performing chemical tests on it. Specific treatments are not available, but gene therapy holds promise for the future.