Background: Recent short-term clinical trials in patients with Duchenne Muscular Dystrophy (DMD) have indicated greater disease variability in terms of progression than expected. In addition, as average life-expectancy increases, reliable data is req
Duchenne muscular dystrophy has a severe disease course, though variability exists. Case reports suggest a milder disease course of patients amenable to exon 44 skipping. In this study, we analyzed this and show that age at wheelchair dependence in patients with a dystrophin deletion requiring exon 44 skipping is postponed compared to patients with a deletion skippable by exon 45, 51 and 53 (10.8 versus 9.8 years; P 0.020). This may be explained by more frequent spontaneous exon 44 skipping in patients with a deletion flanking exon 44. This finding has important implications for the development of future Duchenne trials.
Objective The aim of this study was to evaluate age-related changes in metabolic walking energy expenditure in ambulant boys affected by Duchenne muscular dystrophy over a follow-up period of 12 months. Methods At baseline (T1) and 12 months later (T2), metabolic walking energy expenditure was assessed during a 6-minute walk test at comfortable speed in 14 ambulant boys with Duchenne (age range: 6.0-12.5 years, mean 8.2). Outcome measures derived from the assessment included the 6-minute comfortable walking distance (m) and net-nondimensional energy cost relative to speed-matched control cost (SMC-EC, %). Statistical comparisons were made using a two-way repeated measures ANOVA (factors: time (T1 versus T2) and age (<8 years of age (yoa) versus ≥8 yoa)). Results Over the course of the study, a significant decrease of -28m (−8.2%, p = 0.043) was noted in the walked distance at comfortable speed. Besides, SMC-EC increased with 4.4%, although this change was not significant (p = 0.452). Regarding age groups, boys below 8 yoa showed a smaller annual decrease in the walked distance (−15 m) compared to boys above 8 yoa (−37 m). SMC-EC increased with 10% in the older boys, while in the younger boys it decreased (−2.1%). The main effect of age group on walking distance and SMC-EC however was not significant (p>0.158), and also there were no interaction effects (p>0.248). Conclusions The results of our small study suggest that the natural course of walking performance in ambulant boys with Duchenne is characterized by a decrease in comfortable walking distance and an increase in walking energy cost. The rate of energy cost seems to increase with age, while walking distance decreases, which is opposite from the trend in typically developing children.
A 22-month-old girl had cramps and stiffness of her muscles. After medical history, physical examination and an EMG, a short differential diagnosis based on the symptoms of myotonia was made. Initially, the symptoms were incorrectly assumed to be due to Becker's myotonia, an autosomal recessive condition caused by a mutation in the chloride channel. Molecular analysis did not show a defect in the chloride channel, but instead a defect in the sodium channel of the muscle fibre. Since defects in the sodium channel are responsible for several myotonic diseases, further analysis was necessary. Based on knowledge of the structure and mechanism of the sodium channel and study of literature on cases involving the identical mutation, the diagnosis 'potassium-aggravated myotonia' (PAM) was made. Re-evaluation of the patient showed that her symptoms fitted the diagnosis 'myotonia permanens', the severest form of PAM. She was treated with mexiletine. In myotonia several features can give direction to the diagnosis, including sensitivity to temperature and exercise, and family history. However, it is often necessary to use molecular analysis to be able to diagnose the disease correctly, make a prognosis and predict the risk of recurrence as well as to formulate a treatment plan.
The phenotype of Becker muscular dystrophy (BMD) is highly variable, and the disease may be underdiagnosed. We searched for new mutations in the DMD gene in a cohort of previously undiagnosed patients who had been referred in the period 1985-1995.All requests for DNA analysis of the DMD gene in probands with suspected BMD were re-evaluated. If the phenotype was compatible with BMD, and no deletions or duplications were detected, DNA samples were screened for small mutations.In 79 of 185 referrals, no mutation was found. Analysis could be performed on 31 DNA samples. Seven different mutations, including 3 novel ones, were found. Long-term clinical follow-up is described.Refining DNA analysis in previously undiagnosed cases can identify mutations in the DMD gene and provide genetic diagnosis of BMD. A delayed diagnosis can still be valuable for the proband or the relatives of BMD patients.
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