Clinical characterisation of Becker muscular dystrophy patients predicts favourable outcome in exon-skipping therapy.

OBJECTIVE: Duchenne and Becker muscular dystrophy (DMD/BMD) are both caused by mutations in the DMD gene. Out-of-frame mutations in DMD lead to absence of the dystrophin protein, while in-frame BMD mutations cause production of internally deleted dystrophin. Clinically, patients with DMD loose ambulance around the age of 12, need ventilatory support at their late teens and die in their third or fourth decade due to pulmonary or cardiac failure. BMD has a more variable disease course. The disease course of patients with BMD with specific mutations could be very informative to predict the outcome of the exon-skipping therapy, aiming to restore the reading-frame in patients with DMD. METHODS: Patients with BMD with a mutation equalling a DMD mutation after successful exon skipping were selected from the Dutch Dystrophinopathy Database. Information about disease course was gathered through a standardised questionnaire. Cardiac data were collected from medical correspondence and a previous study on cardiac function in BMD. RESULTS: Forty-eight patients were included, representing 11 different mutations. Median age of patients was 43 years (range 6-67). Nine patients were wheelchair users (26-56 years). Dilated cardiomyopathy was present in 7/36 patients. Only one patient used ventilatory support. Three patients had died at the age of 45, 50 and 76 years, respectively. CONCLUSIONS: This study provides mutation specific data on the course of disease in patients with BMD. It shows that the disease course of patients with BMD, with a mutation equalling a 'skipped' DMD mutation is relatively mild. This finding strongly supports the potential benefit of exon skipping in patients with DMD.

Cardiac abnormalities in a follow-up study on carriers of Duchenne and Becker muscular dystrophy.

OBJECTIVES: Cardiac involvement has been reported in carriers of dystrophin mutations giving rise to Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). The progress of these abnormalities during long-term follow-up is unknown. We describe the long-term follow-up of dilated cardiomyopathy (DCM) in DMD/BMD carriers. METHODS: A long-term follow-up study was performed among Dutch DMD/BMD carriers first analyzed in 1995. A cardiac history was taken, and all carriers were assigned a functional score to assess skeletal muscle involvement. Electrocardiography and M-mode and 2-D echocardiography were performed. DCM was defined as an enlarged left ventricle with a global left ventricle dysfunction or fractional shortening less than 28%. Slow vital capacity of the lung was measured by a hand-held spirometer. RESULTS: Ninety-nine carriers were monitored with a median follow-up of 9 years (range 7.0-10.6 years). Eleven carriers with DCM (10 DMD, 1 BMD) were identified. Nine of them developed DCM in the follow-up period. One of the patients with DCM reported in the 1995 study died of cardiac failure at age 57 years. DCM was more frequently found in carriers who were functionally symptomatic. CONCLUSION: Cardiac abnormalities in DMD/BMD carriers are progressive, as in patients with DMD/BMD.