This Publication Is Searchable The Merck Manual of Diagnosis and Therapy Section 14. Neurologic Disorders Chapter 184. Muscular Disorders Topics Muscular Dystrophies Myopathies Channelopathies Channelopathies Neuromuscular disorders with functional abnormalities due to disturbance of the membrane conduction system, resulting from mutations affecting ion channels. Symptoms can occur at any age, and the range of clinical severity is broad. Myotonia is prominent in the hand muscles, and ptosis is common even in mild cases.
Mental retardation is common.
Severely affected persons die by their early 50s. In several families, the disorder has been linked to a region on chromosome 7 containing a skeletal muscle chloride channel gene. Painless muscle stiffness is most troublesome in the hands, legs, and eyelids and improves with exercise. Weakness is usually minimal. Muscles may become hypertrophied.