Duchenne muscular dystrophy: genetics, diagnosis and care in the UK

Muscle fibres are put under mechanical strain every time they shorten and lengthen. Dystrophin acts like a shock absorber, anchoring the fibre skeleton to the membrane around it. In Duchenne, changes in the DMD gene mean that little or no functional dystrophin is made, so fibres are damaged by ordinary use and are gradually replaced by scar and fat.

Because dystrophin is also present in heart muscle and, to a lesser degree, in the brain, the condition is not confined to the limbs. Some boys have learning, attention or language difficulties alongside the physical picture, and the heart is affected as the years go by.

The DMD gene sits on the X chromosome. A boy has one X chromosome, so a single faulty copy is enough to cause the condition, whereas a girl would normally have a second working copy that compensates. Fathers cannot pass an X-linked change on to their sons.

Many boys inherit the change from a mother who is a carrier, but not all do. Action Duchenne explains that new changes can arise spontaneously and that germline mosaicism, where a change is present in some of a parent's egg or sperm cells without showing up in a routine blood test, can lead to a child being affected even when the parents are well.

Female carriers are not always symptom-free. Action Duchenne notes that carriers may have health considerations of their own, particularly relating to the heart, which is one reason carrier testing and cardiac assessment for female relatives is discussed in clinical genetics.

Parents often notice that a toddler walks late, falls more than other children, finds stairs hard or cannot keep up at nursery. Calf muscles can look unusually bulky, and a child may use his hands to push up his own legs when rising from the floor, a pattern called Gowers' sign. The NHS also lists muscle weakness that worsens with age, joint stiffness and delayed crawling or walking among the features of muscular dystrophy generally.

A raised blood creatine kinase level is often the first objective clue, and a GP who suspects a muscle condition in a child will usually arrange this blood test and refer to paediatric services if it is high.

• Delayed walking or running compared with peers

• Frequent falls and difficulty with steps or hopping

• Enlarged-looking calves

• Using the hands to climb up the thighs to stand (Gowers' sign)

• Tiptoe walking or a waddling gait

Action Duchenne describes creatine kinase blood tests as crucial to diagnosis, with genetic testing used to confirm it and neuromuscular assessment forming part of the work-up. A muscle biopsy is now uncommon because a DNA result can usually answer the question without one.

The type of DMD gene change matters. Some are deletions or duplications of whole sections of the gene, others are small changes within it. The exact change is recorded in the genetic report because it affects which research studies and which genotype-specific medicines a family may later be told about. NHS genetic testing is free when arranged by a hospital specialist, and genetic counselling is offered alongside it.

The NHS describes management of muscular dystrophy as symptom-focused, with physiotherapy, medicines including steroids for Duchenne, cardiac interventions, surgery for complications and respiratory support when needed. Occupational therapy, mobility aids and home adaptations help with daily life.

In practice, care in the UK is led by a specialist neuromuscular team that brings together a paediatric neurologist, physiotherapist, cardiologist, respiratory specialist, endocrinologist, orthopaedic input and nursing support. Steroid treatment needs regular review because of effects on growth, bone strength, weight, blood pressure and mood, so those areas are watched closely.

• Regular physiotherapy and stretching to protect joint movement

• Scheduled heart checks, often with echocardiography and heart-rhythm assessment

• Lung function measurement and, later, breathing support at night if needed

• Bone health review, because steroids and reduced mobility weaken bones

• Spine surveillance for scoliosis

MedlinePlus states that both Duchenne and Becker dystrophy involve cardiomyopathy that typically starts in adolescence and can progress to dilated cardiomyopathy. Heart medicines may be started early to protect the heart muscle rather than waiting for symptoms.

As the diaphragm and chest muscles weaken, cough becomes less effective and breathing during sleep can become shallow. Teams monitor this with lung function tests and sleep assessments and offer cough assistance and non-invasive ventilation when appropriate. Scoliosis can develop as trunk muscles weaken and may be treated with specialist spinal surgery in selected young people.

MedlinePlus reports that boys with Duchenne often become wheelchair-dependent by adolescence and that survival has typically extended into the twenties, although care standards have been changing and individual teams will give a more current picture. Outcomes vary between boys.

Families who have had a child with Duchenne can be referred to clinical genetics to discuss carrier testing for female relatives and options in future pregnancies, including prenatal diagnosis and pre-implantation genetic testing. The NHS notes that prenatal testing is available for pregnancies at risk of muscular dystrophy.