Résumé :
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Congenital myasthenic syndromes (CMS) are a group of inherited disorders in which neuromuscular transmission is impaired, with several possible clinical presentations. The diagnosis of CMS may be particularly difficult in patients with a myopathic pattern in which fluctuations may be overlooked or even absent. Herein, we report two sibs with AChE deficiency with a 16 years follow-up before CMS was suspected. A 30 year-old female achieved normal motor skills, but proximal muscle weakness and progressive postural scoliosis were noted after the second year of life. Facial strength and eye movements were spared. Muscle biopsy was performed when she was aged 12, showing a moderate lipidosis, leading to consider the diagnosis of metabolic myopathy. A thorough workup demonstrated no abnormalities, but L-carnitin and coenzyme Q10 prescription led to dramatic clinical improvement. However, the persistence of muscular weakness led to perform a second muscle biopsy displaying no lipidosis. EMG was thus performed, and special attention was paid to double CMAP in response to single stimulation of median nerve. Neuromuscular transmission study revealed a decremental response of 70%. Although less impaired, her brother aged 32, had presented the same clinical profile from childhood on. His muscular biopsy at age 23 had demonstrated a “non specific dystrophic pattern”. Whereas initial EMGs had shown myogenic patterns, a study of nerve-muscle transmission disclosed the same abnormalities as in her sister. Molecular genetic testing of COLQ gene revealed a missense R340H mutation and a splicing IVS2+1:G->C mutation. This report highlights the importance of a critical and repeated assessment in patients presenting with atypical metabolic or dystrophic features, and the utmost importance of performing a nerve-muscle conduction study in difficult or unsolved cases.
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