Duchenne Muscular Dystrophy

Introduction

Duchenne muscular dystrophy (DMD) is the most common and severe form of hereditary muscular dystrophy. DMD affects 1 in 3,500 live male births. The local prevalence is 1.03 in 10,000 males aged 0-24 years, which is comparable to overseas findings.

Causes

Duchenne muscular dystrophy is caused by a mutation in the DMD gene, which is located on the X chromosome. This mutation prevents the body from producing a muscle protein called dystrophin. The dystrophin protein maintains the health and strength of the muscles. Without dystrophin, muscle cells become fragile and are easily damaged, resulting in progressive weakness.

Mode of Inheritance

DMD is an X-linked recessive disease. Males are primarily affected, while females may be carriers without symptoms or with mild symptoms that present in late adulthood. While it is very rare for girls to develop DMD, it has been well reported that a female carrier with extreme skewing of X-inactivation can present with severe DMD.

Signs and Symptoms

Children with DMD do not exhibit muscle weakness in the first two to four years of life. However, the muscle weakness that starts in early childhood progresses over time. Many affected children develop cardiomyopathy, respiratory problems and scoliosis in their late teens.

At a young age or upon initial presentation, an affected child often:

• appears clumsy and falls easily
• Has trouble walking upstairs, getting up from floor or running
• Uses hands to help get up from the floor (Gowers manoeuvre)
• Walks on toes
• Has enlarged calf muscles (pseudohypertrophy)

By primary school age, there is progressive difficulty in walking. By early adolescence, most affected children have to use a wheelchair. At this stage, as the breathing and truncal muscles weaken, the affected children are at risk of developing weak lung function and spinal curvature. The absence of dystrophin in the cardiac muscles can weaken the heart, potentially causing cardiomyopathy and conduction problems.

Children with DMD are also at increased risk of bone fragility due to the impact of progressive muscle weakness on bone strength and the prolonged use of steroid therapy. The increased risk of long bone fracture could lead to fracture-induced loss of ambulation, and the more common vertebral fractures frequently result in back pain.

More than one-third of boys with DMD have some degree of learning difficulties, language delay and behavioural disorders, especially affecting attention span and focusing, verbal learning and memory, and emotional interaction. Abnormal dystrophin expression in the brain is likely to affect cognition and behaviour.

Diagnosis

Diagnostic evaluation begins with comprehensive history taking followed by a physical examination, and further diagnostic investigations, which can include:

• Blood tests for Creatine Kinase (CK), a muscle enzyme that leaks out of damaged muscle. Very high CK levels (above 10 to 20 times of the upper limit of normal value) suggest an underlying muscular dystrophy.
• Genetic testing to identify the mutation in the DMD gene.
• Muscle biopsy: In a small percentage of cases, the specific DMD mutation may not be identified through standard genetic testing methods. In these cases, a muscle biopsy can be helpful, as it can show whether the dystrophin protein is absent in the muscle cells. If dystrophin is absent or markedly reduced, the diagnosis of DMD is supported, even if the genetic test is negative. A muscle biopsy can also help rule out other muscle diseases that might present similarly to DMD. It can also allow the analysis of genetic expression of the muscle cells, which can help identify the potential underlying mutation site on the DMD gene.

Referral for further evaluation may be necessary if there are concerns about feeding problems, respiratory issues, cardiac problems, musculoskeletal problems and issues related to bone health. Regular monitoring is highly recommended.

Management

The standard management of DMD patients includes medical treatment carried out by a multidisciplinary team to control symptoms and improve quality of life. The care team comprises a paediatric neurologist specialising in neuromuscular diseases, a respiratory specialist, a cardiologist, an endocrinologist, an orthopaedic surgeon, other specialists, and rehabilitation teams including physiotherapists, occupational therapists, speech therapists, orthotists and dietitians.

After the starting of steroid therapy, ongoing monitoring of motor, breathing, swallowing and heart performances, weight control, contractures and spinal curve, bone health and eye status are important.

Medical treatments

• Disease-modifying treatments including corticosteroids, such as prednisolone and deflazacort, have been shown to slow down the progression of muscle weakness and cardiomyopathy, improve lung function, delay scoliosis, and prolong survival.
• Cardiac treatment: ACE (angiotensin-converting enzyme) inhibitors may slow down the progression of cardiomyopathy, and has been recommended as an early prophylactic treatment.
• Treatment for bone health: Regular supplements of Vitamin D and calcium are recommended to ensure good bone health. For those confirmed to have osteoporosis, regular treatment with bisphosphonate will be initiated.

Rehabilitation therapies

• Physiotherapy: This includes regular range of motion and stretching exercises to prevent contractures. Gentle exercises, often a combination of hydrotherapy and recreational-based activities, can help to prevent muscle atrophy due to disuse.
• Orthosis: The use of braces can keep the muscles and tendon stretched, slowing down the progression of contractures. Spinal brace can slow down the progression of scoliosis.
• Mobility aids: Canes, walkers, and wheelchairs can assist in maintaining mobility and independence. Stander can support passive standing.

Breathing assistance

Older children may benefit from the use of a ventilator to assist breathing during sleep.

Surgery

Surgery may be needed to correct contractures or spinal curvature.

Follow-up Care

Comprehensive care model in HKCH

A one stop Neurology (Neuromuscular) – Endocrine (Bone health) – Orthopaedic Combined Clinic has been established for all children with DMD.

• Regular motor evaluations by the physiotherapy team are carried out before the multidisciplinary clinics.
• Regular cardiac follow-up by the cardiology team is provided for those on cardiac treatment.
• Regular eye follow-up by the ophthalmology team is provided for those on steroid treatment.
• The DMD multidisciplinary team works closely with the parent hospital team to provide personalised and coordinated care for each individual patient.

Research participation in HKCH

Patients can participate in clinical trials for new treatments. This not only provides them with access to potentially beneficial therapies before they are widely available, but also contributes to knowledge about the treatment's effectiveness and safety. Research can also facilitate the development of guidelines for diagnosing and managing DMD. Adherence to these guidelines can lead to more standardized and effective care.

DMD is a muscle disease characterised by progressive deterioration, with multi-system involvements at later stages. Deterioration can be effectively managed with a good standard of care and early initiation of disease-modifying treatments. The HKCH team is committed to providing personalised treatment through multidisciplinary team monitoring and timely intervention tailored to individual child’s needs. We strive to combine clinical care and research, aiming to advance the care and improve outcomes for individuals with DMD.

References

Chan SHS, Lo IFM, Cherk SWW, Cheng WW, Fung ELW, Yeung WL, Ngan M, Lee WC, Kwong L, Wong SN, Ma CK, Tai SM, Ng GSF, Wu SP, Wong VCN. Prevalence and Characteristics of Chinese Patients with Duchenne and Becker Muscular Dystrophy: A Territory Wide Collaborative Study in Hong Kong. Child Neurol Open. 2015 May 26;2(2):2329048X15585345. doi: 10.1177/2329048X15585345.

Acknowledgement

Principal author: Dr Sophelia Chan on behalf of Neurology Team, HKCH

Initial posting: Nov 2025

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