Muscular dystrophy (MD) is an umbrella term used to describe a group of over 30 genetic conditions that cause progressive, irreversible muscle weakness and wastage (MDF 2021; Better Health Channel 2019).
MD is part of a wider group of over 75 neuromuscular conditions (NMCs) (MDF 2021) - disorders that impair the functioning of nerves that control the voluntary muscles (e.g. muscles in the arms and legs) (RCN 2021).
Muscular dystrophies are caused by mutations affecting various genes that code the proteins responsible for the structure and function of the muscles, making them weaker, fragile and susceptible to damage. This leads to progressive disability (NHS 2018; myDr 2016).
The type of MD that an individual has depends on the specific gene mutation that has occurred (Better Health Channel 2019).
Different types of MD also have different inheritance patterns, including:
(NHS 2018; Monckton & Guglieri 2018)
Sometimes genes will undergo a non-inherited, spontaneous (‘de novo’) mutation for no apparent reason (usually during the early development of the embryo). An individual who undergoes de novo gene mutation can develop MD even if they have no family history of the disorder (Better Health Channel 2019; NHS 2018; NCI 2016).
Muscular dystrophies vary in severity and can affect different muscles (Better Health Channel 2019).
There are eight main types of muscular dystrophy that will be discussed in this article.
Inheritance pattern: X-linked recessive
Affected gene: The DMD gene, which is responsible for coding the protein dystrophin. Dystrophin maintains the structure of muscle cells and protects the muscles from damage when they contract. People with DMD produce almost no functional dystrophin.
DMD primarily affects males and the average age of symptom onset is two to three years. Initially, DMD affects the proximal muscles (shoulders, upper arms, hips and thighs). Over time, the distal muscles near the extremities will also be affected, leading to progressive weakness and scoliosis. This may eventually lead to acute respiratory failure.
Symptoms include:
DMD is severe and may cause complications such as:
(Better Health Channel 2019; MDA 2021)
Inheritance pattern: X-linked recessive
Affected gene: DMD gene. People with BMD generally produce shortened, partially functional dystrophin.
BMD is similar to DMD and is inherited in the same way, however, BMD is less severe. The age of symptom onset ranges from 5 to 60 years. Symptoms are similar to those of DMD but slower and milder. BMB tends to have a less predictable disease progression.
(Better Health Channel 2019; MDA 2021)
Inheritance pattern: Autosomal recessive (most common)
Affected gene: Depends on the type of CMD
CMD is an umbrella term describing a range of muscular dystrophies present at or soon after birth. CMDs vary in severity and progression. They include:
Infants with CMD may display symptoms such as:
(Better Health Channel 2019; MDA 2021)
Inheritance pattern:
Affected gene: Depends on the subtype of LGMD
LGMD is a category of MD with many different subtypes, characterised by weakness and atrophy of the shoulders, upper arms, hips and thighs (limb-girdle muscles). The age of symptom onset, severity and rate of progression vary greatly depending on the subtype, but most progress slowly and affect the body symmetrically.
Symptoms may include:
(Better Health Channel 2019; MDA 2021)
Inheritance pattern: Autosomal dominant
Affected gene: DUX4 gene
FSHD predominantly causes weakness in the face, shoulders and upper arms. Symptom onset usually occurs before the age of 20 but may begin as late as during someone’s 50s. FSHD progresses slowly and is considered less serious than other muscular dystrophies. The cardiac and respiratory systems are not usually affected.
Symptoms may include:
(Better Health Channel 2019; Monckton & Guglieri 2018; MDA 2021)
Inheritance pattern: Autosomal dominant
Affected gene:
DM is the most common type of MD in adults. It is characterised by myotonia (being unable to relax the muscles voluntarily) and non-muscular symptoms in addition to muscle weakness. The distal muscles are usually affected first. Tissues and organs can also be impacted.
There are two types of DM:
Symptoms may include:
(Better Health Channel 2019; MDA 2021)
Inheritance pattern:
Affected gene: PABPN1 gene
OPMD is a rare, adult-onset type of MD that usually presents between the mid-40s and 50s. It is characterised by a slowly progressing weakness of the eyelid and throat muscles. The main symptoms are drooping eyelids and dysphagia.
(Better Health Channel 2019; MDA 2021.; Cedars-Sinai 2019)
Inheritance pattern:
Affected gene: EMD, LMNA or FHL1 gene
EDMD usually presents at around the age of 10. Early symptoms include toe-walking, difficulty bending the elbows, weakness of muscles (in the shoulders, upper arms and calves) and stiff joints (in the elbows, neck and heels). Many people develop cardiac issues by the age of 20.
(MDA 2021; Bonne, Leturcq & Yaou 2019)
Diagnosis may involve:
(Better Health Channel 2019; Healthdirect 2020)
While there is no cure for MD, symptoms can be managed and disease progression can be slowed through medicines and physical therapy (Healthdirect 2020).
Depending on the individual and the type of MD they are living with, treatment strategies may include:
(Healthdirect 2020)
The overall goal of treatment and management is to optimise the patient’s quality of life and mobility for as long as possible so that they can live a fulfilling, enjoyable life with the least amount of discomfort (Healthdirect 2020).
Question 1 of 2
Which type of MD is caused by the same mutated gene as Duchenne muscular dystrophy?
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