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What is Facioscapulohumeral Muscular Dystrophy?

Facioscapulohumeral muscular dystrophy is a disorder characterized by muscle weakness and wasting (atrophy). This condition gets its name from the areas of the body that are affected most often: muscles in the face (facio-), around the shoulder blades (scapulo-), and in the upper arms (humeral). The signs and symptoms of facioscapulohumeral muscular dystrophy usually appear in adolescence. However, the onset and severity of the condition varies widely. Milder cases may not become noticeable until later in life, whereas rare severe cases become apparent in infancy or early childhood.

Weakness involving the facial muscles or shoulders is usually the first symptom of this condition. Facial muscle weakness often makes it difficult to turn up the corners of the mouth when smiling, drink from a straw, or whistle. Weakness in muscles around the eyes can prevent the eyes from closing fully while a person is asleep, which can lead to dry eyes and other eye problems. For reasons that are unclear, weakness may be more severe in one side of the face than the other. Weak shoulder muscles tend to make the shoulder blades (scapulae) "stick out" from the back, a common sign known as scapular winging. Weakness in muscles of the shoulders and upper arms can make it difficult to raise the arms over the head or throw a ball.

The muscle weakness associated with facioscapulohumeral muscular dystrophy worsens slowly over decades and may spread to other parts of the body. Weakness in muscles of the lower legs can lead to a condition called foot drop, which affects walking and increases the risk of falls. Muscular weakness in the hips and pelvis can make it difficult to climb stairs or walk long distances. Additionally, affected individuals may have an exaggerated curvature of the lower back (lordosis) due to weak abdominal muscles. About 20 percent of affected individuals eventually require the use of a wheelchair.

Additional signs and symptoms of facioscapulohumeral muscular dystrophy can include mild high-tone hearing loss and abnormalities involving the light-sensitive tissue at the back of the eye (the retina). These signs are often not noticeable and may be discovered only during medical testing. Rarely, facioscapulohumeral muscular dystrophy affects the heart (cardiac) muscle or muscles needed for breathing.

How Common is Facioscapulohumeral Muscular Dystrophy?

Facioscapulohumeral muscular dystrophy has an estimated prevalence of 1 in 20,000 people.

What are the Genetic Changes related to
Facioscapulohumeral Muscular Dystrophy?

Facioscapulohumeral muscular dystrophy results from a deletion of genetic material from a region of DNA known as D4Z4. This region is located near one end of chromosome 4. The D4Z4 region normally consists of 11 to more than 100 repeated DNA segments, each of which is about 3,300 DNA base pairs (3.3 kb) long. However, in people with facioscapulohumeral muscular dystrophy the D4Z4 region on one copy of chromosome 4 is abnormally short, containing between 1 and 10 repeats.

It is uncertain how a shortened D4Z4 region causes progressive muscle weakness and wasting. Researchers have proposed several possible mechanisms, but none have yet been proven. It appears that the D4Z4 region influences the activity of other genes located nearby on chromosome 4. An abnormally short D4Z4 region may somehow disrupt the normal regulation of these genes. However, it is unclear which genes are influenced by D4Z4 and what role, if any, those genes play in muscle cells. Researchers suspect that genetic factors other than the shortened D4Z4 region may also be involved in facioscapulohumeral muscular dystrophy.

Read more about chromosome 4.

Can Facioscapulohumeral Muscular Dystrophy be Inherited?

This condition is inherited in an autosomal dominant pattern, which means one copy of the shortened D4Z4 region in each cell is sufficient to cause the disorder. In most cases, an affected person inherits the deletion from one affected parent. Other people with facioscapulohumeral muscular dystrophy have no history of the disorder in their family; these cases are described as sporadic and are caused by a new (de novo) D4Z4 deletion on one copy of chromosome 4.

Where can I find Information about Diagnosis or Management of Facioscapulohumeral Muscular Dystrophy?

These resources address the diagnosis or management of facioscapulohumeral muscular dystrophy and may include treatment providers.

You might also find information on the diagnosis or management of facioscapulohumeral muscular dystrophy in Educational resources and Patient support.

General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.

To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.

Where can I Find Additional Information about
Facioscapulohumeral Muscular Dystrophy?

You may find the following resources about facioscapulohumeral muscular dystrophy helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other Names do People use for
Facioscapulohumeral Muscular Dystrophy?

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.

What if I still have Specific Questions about
Facioscapulohumeral Muscular Dystrophy?

Ask the Genetic and Rare Diseases Information Center.

Where can I find General Information about Genetic Conditions?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What Glossary Definitions help with understanding
Facioscapulohumeral Muscular Dystrophy?

atrophy - autosomal - autosomal dominant - cardiac - cell - chromosome - deletion - DNA - DNA base - foot drop - kb - lordosis - muscular dystrophy - pelvis - prevalence - progressive muscular dystrophy - retina - sign - sporadic - symptom - tissue - wasting

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

See also Understanding Medical Terminology.

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