Symptomatic Form Of Muscular Dystrophy Of Duchenne And Becker In Female Carriers

A rare, genetic muscular dystrophy affecting female carriers and characterized by variable degrees of muscle weakness due to progressive skeletal myopathy, sometimes associated with dilated cardiomyopathy or left ventricle dilation.

Epidemiology

The prevalence is unknown. Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) primarily affect males and only a small percentage of female carriers have been reported to manifest symptoms of these diseases (24% of female carriers from families with DMD and 19% of female carriers from families with BMD).

Clinical description

Symptomatic female carriers usually present later than males with DMD or BMD. The muscle weakness is generally less severe than in affected males and is usually proximal and, unlike males, has an asymmetric distribution. The upper limbs may be weaker than the lower limbs. Myalgia and cramps have also been reported. The serum creatine kinase level is raised. Some patients may present with cardiac manifestations alone.

Etiology

DMD and BMD are both X-linked recessive diseases and are caused by dystrophin deficiency in skeletal and heart muscles due to variants in the DMD gene (Xp21.2). Females with clinical features of DMD and BMD are usually carriers of X-chromosome rearrangements and display skewed X-inactivation.

Diagnostic methods

Diagnosis can be confirmed by molecular testing of the DMD gene (Xp21.2-p21.1). Muscle biopsy shows a mosaic pattern of dystrophin expression.

Differential diagnosis

Differential diagnoses includes Turner syndrome.

Genetic counseling

The pattern of inheritance is X-linked and genetic counseling should be offered to affected families. Female siblings of a proband with DMD or BMD have a 50% risk of being carriers. Female offspring of a female carrier have a 50% risk of becoming a carrier, male offspring have 50% of inheriting DMD or BMD depending on the mutation. In female carriers, the penetrance of symptoms is variable; most carriers are asymptomatic.

Management and treatment

Management of symptomatic patients should be multidisciplinary, severely affected patients may require treatment with corticosteroids as in DMD. Physiotherapy and orthotics should be used to prevent joint contractures. Respiratory function should be monitored regularly and nocturnal hypoventilation treated with BiPAP (bilevel positive airway pressure). There should be regular cardiac monitoring of all female carriers of BMD and DMD, symptomatic and asymptomatic, with early treatment using ACE inhibitors and or beta-blockers.

Prognosis

Female carriers of DMD and BMD have been shown to be at increased risk of developing dilated cardiomyopathy, although the impact on survival is uncertain.