Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (sometimes switched as faciohumeroscapular) (FSHMD, FSHD or FSH), which is also known as Landouzy-Dejerine, is a usually autosomal dominant inherited form of muscular dystrophy (MD) that initially affects the skeletal muscles of the face (facio), scapula (scapulo) and upper arms (humeral). While it is widely stated to be the third most common genetic disease of skeletal muscle, a 2008 analysis of rare diseases listed FSHD as the most prevalent form of MD at 7/100,000.

Symptoms may develop in early childhood and are usually noticeable in the teenage years with 95% of affected individuals manifesting disease by age 20 years. A progressive skeletal muscle weakness usually develops in other areas of the body as well; often the weakness is asymmetrical. Life expectancy is normal, but up to 15% of affected individuals become severely disabled and eventually must use a wheel chair. Non-muscular symptoms frequently associated with FSHD include subclinical sensorineural hearing loss and retinal telangiectasia.

In more than 95% of known cases, the disease is associated with deletions of the D4Z4 repeat in the 4q35 subtelomeric region of Chromosome 4. Seminal research published in August 2010 now shows that a second mechanism is needed for FSHD, which for the first time provides a unifying theory for the underlying genetics of FSHD. The second mechanism was found to be a "toxic gain of function" of the DUX4 gene which is the first time in the history of genetic research that a "dead gene" has been found to "wake up" and cause disease.