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Título

Congenital myopathy with MYBPC1 gene mutation associated with muscular activity tremor-like

RESUMO

Case Presentation: A 10-year-old boy, born with cleft palate that was corrected at age 1.5, with a history of delayed language development, presented for assessment of tremor. Relatives inform the presence of postural and action tremor since birth. Patient complained of tremor interfering with his daily living activities associated with myalgia affecting his lower-limbs, particularly when running. On physical examination, it was noted proximally-predominant tetraparesis and postural and action tremor. EMG showed notably proximal myopathy without complex repetitive or myotonic discharges. Surface electromyographic study of tremor, with a channel recording the flexor and another one recording the extensor muscles of forearms, showed continuous muscular activity in the extensor muscles during wrist extension, with no bursts (typical sign of tremor). Brain MRI was normal. There was no family history of neurological diseases. Given the clinical picture suggestive of myopathy, a neuromuscular panel was ordered and the genetic test confirmed MYBPC1 gene mutation, thus, a congenital myopathy.
Discussion: Congenital myopathies are a group of inherited muscle disorders clinically characterized by hypotonia and weakness. It usually begins at birth and has a static or slowly progressive clinical course. Diagnosis and classification of congenital myopathies has historically been based on clinical features and histopathology. Nevertheless, recent advances in genetics have changed diagnostic practice. The gene MYBPC1 encodes a member of the myosin-binding protein C Family (sMyBP-C), a modular sarcomeric protein that exerts structural and regulatory roles through dynamic interactions with actin and myosin filaments of the muscle. This protein has three isoforms: cardiac, fast skeletal and slow skeletal. The main roles attributed to the MyBP-C family are the stabilization of thick filaments and the regulation of the cross-bridge cycle. Recent studies demonstrate that the genesis of tremor may be associated with mutation in some gene positions; this hypothesis is supported by the formation of cross-bridges by the sarcomeric protein.
Final comments: Constant advances in the field of genetics have led to a significant increase in knowledge of the broad phenotypic spectrum, including overlapping phenotypes, of congenital myopathies.