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DMD
dystrophin
The DMD gene provides instructions for producing dystrophin, a protein essential for maintaining the structural integrity of muscle fibres, particularly in skeletal and heart muscles. Dystrophin acts as an anchor within muscle cells, connecting the internal cytoskeleton to the external matrix, thereby protecting muscles from damage during contraction and relaxation.
DMD is located on the short (p) arm of chromosome X, at band Xp21.2-p21.1. Arm ratio per GRCh38 - banding schematic.
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Overview
The DMD gene is one of the largest genes in the human genome, responsible for encoding the dystrophin protein. This protein plays a critical role in muscle function, predominantly found in skeletal muscles, which are responsible for movement, and cardiac muscle, which forms the heart wall. Dystrophin helps maintain the structural integrity of muscle cells, safeguarding them from injury during the repeated cycles of muscle contraction and relaxation.
While its primary role is in muscle tissue, smaller quantities of dystrophin are also present in nerve cells within the brain. Variants in the DMD gene can lead to a spectrum of conditions, most notably Duchenne muscular dystrophy and Becker muscular dystrophy, both of which are characterised by progressive muscle weakening and wasting.
What the gene does
Dystrophin, the protein encoded by the DMD gene, is a vital component of the dystrophin-associated protein complex (DAPC) found within muscle fibres. In both skeletal and cardiac muscle, this complex functions as a crucial link between the muscle cell's internal structural framework, known as the cytoskeleton, and the extracellular matrix - the network of proteins and other molecules surrounding the cell. This anchoring function is essential for strengthening muscle fibres and protecting them from mechanical stress and injury that occurs as muscles contract and relax.
Beyond its structural role, the dystrophin complex may also contribute to cell signalling pathways by interacting with proteins involved in transmitting and receiving chemical signals. In nerve cells within the brain, dystrophin's precise function is less understood. However, research indicates that it is important for the normal structure and function of synapses, which are the specialised junctions where nerve cells communicate with each other.
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Chromosome location
The DMD gene is located on the short (p) arm of the X chromosome, specifically at position Xp21.2-p21.1. This region is part of the X chromosome's genetic material. As an X-linked gene, its inheritance pattern means that conditions associated with DMD variants typically affect males more severely than females, as males have only one X chromosome.
Protein structure
The dystrophin protein is exceptionally large, comprising 3685 amino acids, and exhibits a complex domain architecture essential for its function. At its N-terminus, it contains an Actin-binding region (amino acids 1-240), which includes two Calponin-homology (CH) domains: CH 1 (amino acids 15-119) and CH 2 (amino acids 134-240). Within this N-terminal region, there is also an ANK2- and ANK-3 binding region (amino acids 63-72).
The central rod domain of dystrophin is characterised by a series of spectrin-like repeats, including Spectrin 1 (amino acids 339-447), Spectrin 2 (amino acids 448-556), Spectrin 3 (amino acids 559-667), Spectrin 4 (amino acids 719-828), Spectrin 5 (amino acids 830-934), Spectrin 6 (amino acids 943-1045), Spectrin 7 (amino acids 1048-1154), Spectrin 8 (amino acids 1157-1263), Spectrin 9 (amino acids 1266-1367), and Spectrin 10 (amino acids 1368-1463). A region involved in Interaction with SYNM (amino acids 1415-1913) is also present within the larger central segment.
Key variants
Over 2,000 different genetic variants have been identified in the DMD gene. These variants can range from large deletions or duplications of entire gene segments to smaller changes, such as point mutations. The type and location of a DMD variant can influence the severity and presentation of associated conditions. Many variants lead to a non-functional or entirely absent dystrophin protein, while others result in a partially functional protein. The X-linked inheritance pattern means that males, with only one X chromosome, are typically more severely affected by pathogenic variants in DMD.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
g.31147519dup | - | Pathogenic | ★★☆☆ | not provided |
c.10453dup | p.Leu3485Profs | Pathogenic | ★★☆☆ | Becker muscular dystrophy |
c.10000del | p.Tyr3334fs | Pathogenic/Likely pathogenic | ★★☆☆ | Duchenne muscular dystrophy |
c.10033C>T | p.Arg3345Ter | Pathogenic | ★★☆☆ | Duchenne muscular dystrophy |
c.10062T>A | p.Tyr3354Ter | Pathogenic | ★★☆☆ | not provided |
c.1006G>T | p.Glu336Ter | Pathogenic | ★★☆☆ | Duchenne muscular dystrophy |
c.10077T>G | p.Tyr3359Ter | Pathogenic | ★★☆☆ | Duchenne muscular dystrophy |
c.10086+1G>A | - | Pathogenic | ★★☆☆ | not provided |
c.10086+1G>T | - | Pathogenic | ★★☆☆ | not provided |
c.10086+2T>C | - | Pathogenic | ★★☆☆ | not provided |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the DMD gene are the underlying cause of several inherited conditions. The most well-known are Duchenne muscular dystrophy and Becker muscular dystrophy, which primarily affect males and lead to progressive muscle weakness and wasting, alongside dilated cardiomyopathy. Additionally, specific DMD gene variants can cause X-linked dilated cardiomyopathy, a heart condition characterised by an enlarged and weakened heart muscle, which may occur without significant skeletal muscle weakness.
Inheritance pattern
Conditions caused by pathogenic DMD variants typically follow x-linked inheritance.
X-linked recessive: sons of a carrier mother have a 50% chance of being affected. Daughters have a 50% chance of being carriers.
UK clinical status
The DMD gene is an important gene within the UK's NHS Genomic Medicine Service. It is included on several diagnostic and screening panels due to its clinical significance. These include panels for Acute rhabdomyolysis, Congenital muscular dystrophy, Dilated and arrhythmogenic cardiomyopathy, Duchenne or Becker muscular dystrophy, and Paediatric or syndromic cardiomyopathy, among others. Its presence on these panels indicates its established role in the diagnosis and management of a range of muscular and cardiac conditions within the UK healthcare system.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
For individuals with DMD gene variants, lifestyle management typically focuses on maintaining muscle function and overall well-being. Regular, appropriate physical activity, as recommended by healthcare professionals, may help manage muscle strength and mobility, though overexertion should be avoided. A balanced diet rich in essential nutrients supports general health. Maintaining a healthy weight can also help reduce stress on muscles and the cardiovascular system. However, specific lifestyle interventions to prevent the onset or progression of conditions related to DMD variants are not well-established, and any changes should be discussed with a healthcare provider.
Supplement considerations
There is no conclusive evidence that any specific dietary supplements can prevent the development or progression of conditions associated with DMD gene variants. Some research explores the role of various nutritional compounds in muscle health, but these studies have not demonstrated a clear benefit for individuals with DMD-related conditions. Individuals considering any supplements should consult their healthcare provider to discuss potential benefits, risks, and interactions with other medications.
Frequently asked questions
What is the primary function of the DMD gene?
The DMD gene provides instructions for making dystrophin, a protein vital for strengthening muscle fibres. It acts as an anchor, connecting the internal structure of muscle cells to the external support network, protecting them from damage during muscle movement.
How does DMD relate to Duchenne and Becker muscular dystrophy?
Pathogenic variants in the DMD gene are the cause of Duchenne and Becker muscular dystrophies. These conditions result from insufficient or non-functional dystrophin, leading to progressive muscle weakness and wasting, predominantly affecting males.
Is the DMD gene associated with heart conditions?
Yes, pathogenic variants in the DMD gene are associated with heart conditions. Dilated cardiomyopathy, a weakening and enlargement of the heart muscle, is a common feature of Duchenne and Becker muscular dystrophies, and some specific variants can cause X-linked dilated cardiomyopathy as a primary condition.
Why are males typically more affected by DMD gene variants?
The DMD gene is located on the X chromosome. Since males have only one X chromosome, a pathogenic variant in their single DMD gene will typically lead to the condition. Females have two X chromosomes, so if one carries a pathogenic variant, the other X chromosome can often compensate, making them carriers or exhibiting milder symptoms.
Can lifestyle changes prevent DMD-related conditions?
There is no evidence that lifestyle changes can prevent the onset of conditions caused by DMD gene variants. However, managing lifestyle factors such as appropriate physical activity and a balanced diet, under medical guidance, can help support general health and manage symptoms for individuals with these conditions.
References
- Nakamura A. X-Linked Dilated Cardiomyopathy: A Cardiospecific Phenotype of Dystrophinopathy. Pharmaceuticals (Basel, Switzerland). 2015. PMID: 26066469
- Neri M, Valli E, Alfano G. The absence of dystrophin brain isoform expression in healthy human heart ventricles explains the pathogenesis of 5' X-linked dilated cardiomyopathy. BMC medical genetics. 2012. PMID: 22455600
- Le Rumeur E, Winder SJ, Hubert JF. Dystrophin: more than just the sum of its parts. Biochimica et biophysica acta. 2010. PMID: 20472103
- Ervasti JM. Dystrophin, its interactions with other proteins, and implications for muscular dystrophy. Biochimica et biophysica acta. 2007. PMID: 16829057
- Aartsma-Rus A, Van Deutekom JC, Fokkema IF. Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule. Muscle & nerve. 2006. PMID: 16770791
- Cohen N, Muntoni F. Multiple pathogenetic mechanisms in X linked dilated cardiomyopathy. Heart (British Cardiac Society). 2004. PMID: 15253946
- Muntoni F, Torelli S, Ferlini A. Dystrophin and mutations: one gene, several proteins, multiple phenotypes. The Lancet. Neurology. 2003. PMID: 14636778
- Anderson JL, Head SI, Rae C. Brain function in Duchenne muscular dystrophy. Brain : a journal of neurology. 2002. PMID: 11834588
- Ehmsen J, Poon E, Davies K. The dystrophin-associated protein complex. Journal of cell science. 2002. PMID: 12082140
- Biggar WD, Klamut HJ, Demacio PC. Duchenne muscular dystrophy: current knowledge, treatment, and future prospects. Clinical orthopaedics and related research. 2002. PMID: 12151886
- Ferlini A, Sewry C, Melis MA. X-linked dilated cardiomyopathy and the dystrophin gene. Neuromuscular disorders : NMD. 1999. PMID: 10407857
- Adam MP, Bick S, Mirzaa GM. Dystrophinopathies. 1993. PMID: 20301298