Background: X-linked dystrophinopathy, resulting from mutations in the dystrophin gene, is the
most common cause of inherited myopathy in males. On the molecular level, Becker muscular
dystrophy (BMD) is caused by deletions, point mutations, or duplications in the dystrophin
gene. Although the genetic defect and the impaired formation of dystrophin are already
present from birth, males with Duchenne muscular dystrophy (DMD) or the milder BMD
are born with normal muscle function and develop progressive muscle weakness as they
age. In BMD, the pattern of symptom development resembles that of DMD, but with a
later, and much slower rate of progression.
Case: We report the case of a 2.5-year-old boy showing an elevation of the Creatine kinase
(CK) up to 25,000 U/L associated with an infection and hepatosplenomegaly. The boy
revealed age-appropriate physical development; in particular, an unremarkable muscle
status as well as a timely achievement of the motoric milestones. After excluding
infection as a cause of the CK-elevation, a genetic analysis was performed in the
family for suspected dystrophinopathy. DNA sequence analysis did neither detect a
duplication nor a deletion, but an unknown de novo missense mutation (exon 6: c.434G > C;
p.Arg145Pro) in the dystrophin gene of the index patient and as heterozygous mutation
in his mother. The maternal grandparents had normal dystrophin gene analysis.
A muscle biopsy in the index patient showed partial but insufficient function of the
protein dystrophin and established the diagnosis of BMD.
Conclusion: The progression of BMD is highly variable. Nevertheless, 90% of all patients develop
a cardiomyopathy (CM), which is fatal in 50% of all cases. Therefore, it is important
to consider dystrophinopathy in the differential diagnosis of persistent hyperCKaemia
even in asymptomatic patients. In those, clinical follow-up, genetic analysis, and
a muscle biopsy, should be performed to closely monitor for the development of CM.
Discovering CM at an early stage should help initiate an early treatment, reducing
the progress of cardiac insufficiency.
Keywords: Becker muscular dystrophy, HyperCKaemia, dystrophinopathy.
