Facioscapulohumeral muscular dystrophy (FSHD)

Facioscapulohumeral muscular dystrophy (FSHD) is caused by activation of the DUX4 gene. The gene is located on chromosome 4 (4q35) in a region with DNA sequences designated D4Z4. There are several different types of FSHD. These are arranged according to the underlying genetic cause of DUX4 activation.

Around 95% of individuals with FSHD have a deletion (loss) of genetic material in the D4Z4 region. This reduces inactivation of DUX4 and leads to the form of the disorder known as FSHD1. In around 5% of individuals with FSHD both chromosomes in chromosome 4 are affected. This form of the disorder is designated FSHD2 and causes the same symptoms as with FSHD1, although with later onset.

FSHD is a neuromuscular disorder that mainly affects the muscles in the face, shoulders, and upper arms. Initial signs and symptoms usually appear during the teenage years although a number of individuals exhibit symptoms in early childhood. Approximately half of those suffering from the disorder have impaired hearing. Some find it difficult to close their eyelids and consequently sleep with their eyes open. The muscles that control eye movement are not usually affected. Some individuals have reduced lung function, sleep apnoea, and in rare cases respiratory failure. The degree of severity of the disorder varies considerably from one person to another. In rare cases the central nervous system could be affected, which could lead to learning difficulties and epilepsy. Life expectancy is not affected.

Treatment is aimed at alleviating the symptoms. The functioning of the arms can be improved by scapular (shoulder blade) reconstruction. Sleep apnoea could be eased with the aid of breathing support.

FSHD1, FSHD2, Facioscapulohumeral myopathy, Landouzy-Dejerine dystrophy, Landouzy-Dejerine myopathy

It is common for the lower facial muscles to be weakened. This change usually takes place slowly and is often difficult to detect in children. In the majority of cases the weakness affects the cheek muscles (m. zygomaticus major) and lip muscles (m. orbicularis oris) although the jaw and the tongue could be slightly affected. Facial weakness is often asymmetric. This could give rise to reduced facial expression, such as the ability to smile and to a lesser degree to pout. It could also affect the ability to eat, talk, and saliva control. In the majority of cases these problems are only mild. Individuals with FHSD often have difficulty with oral motor activities, such as drinking through a straw, whistling, or blowing up balloons. As the effect on the facial muscles is not symmetrical, the disorder could give rise to facial asymmetry. Individuals with FHSD could have an increased tendency to grind/press their teeth during the daytime, causing pain in the face and neck. The weakness could also affect the ability to oral cleansing after a meal. Speech could be affected by weak lip muscles (dysarthria), particularly when pronouncing the consonants /m/, /b/, and /p/. The ability to swallow is not usually affected.

• Due to muscle weakness in the shoulders and upper arms, individuals with FSHD could have difficulty coping with dental treatment and tooth brushing, thus requiring enhanced preventive dental care. Collaboration between a dental hygienist and an occupational therapist is recommended to find suitable aids and adaptations.
• When providing dental treatment it is important to bear in mind that a person with breathing problems would find it difficult to lean backwards. Adaptation of the treatment chair – using stabilised cushions for example – could help the patient find a relaxed position while being treated.
• Individuals with FSHD could have difficulty getting into and out of the dental treatment chair unaided.
• Pain in the temporomandibular joint and masticatory muscles is common and ought to be investigated by a dentist or stomatognathic physiologist.
• Malocclusion could result from pressure caused by breathing support or tangible muscle weakness and in that case an orthodontist ought to be consulted at an early stage.
• Oral motor skills are investigated by a speech pathologist. Guidance and low-intensity training of oral motor skills can help patients with FSHD to find compensatory techniques to help them speak and eat.
• If required, speech pathologist can investigate and test alternative and augmentative communication techniques.