Family study allows more optimistic prognosis and genetic counselling in a child with a deletion of exons 50-51 of the dystrophin gene

In frame deletions of exons encoding the central rod domain of dystrophin have been associated with a highly variable phenotype, including asymptomatic individuals. The lack of family history impairs accurate genetic counselling. We report on a 4-year-old child suffering from transient episodes of limping at the age of 2 and several episodes of fall since the age of 3. Clinical examination did not show muscle weakness. CPK levels were increased (1300 UI). EMG was normal. Muscle histology showed a rhabdomyolysis without features of muscular dystrophy. Immunolabelling for dystrophin, merosin and dysferlin were normal. Western blot analysis of muscular proteins showed reduced-size dystrophin bands and a slightly reduced intensity for dystrophin, alpha and gamma-sarcoglycan. Multiplex PCR of the dystrophin gene showed an in-frame deletion of exons 50-51, predicted to be associated to a Becker type of dystrophinopathy. Intragenic markers and quantitative PCR suggested maternal inheritance. This was confirmed by testing the maternal grand-parents, revealing that the asymptomatic 69-year-old grand father was a carrier. Three additional healthy males, whose ages ranged from 28 to 55 years and who were asymptomatic, also carried the mutation. The proband became spontaneously asymptomatic and cardiac echography was normal. In light of these data, genetic counselling was more reassuring and the mutation carrier maternal aunt, who was pregnant, decided to continue the pregnancy. This case report emphasizes the importance of family molecular analysis, especially in males from the maternal lineage, for genetic counselling of dystrophinopathies associated to atypical features or to an isolate increase of muscular enzymes level in a young boy with no positive family history.