T en patients with acid maltase deficiency (AMD) (two infantile, one childhood, and seven adult cases) have been investigated at the Mayo Clinic to date. The clinical, electromyographic, histochemical, ultrastructural and biochemical features of the disease at different ages are compared and summarized. The clinical features of 26 previously published and biochemically proved cases of AMD are reviewed. The syndrome may occur at any age. In infants, enlargement of heart, liver and tongue as well as generalized weakness is usually present, and death occurs before the age of two years. In children, limb girdle weakness is usually present but organomegaly and respiratory muscle involvement are variable, and death occurs before the end of the second decade. In adults, the symptoms present in the third or subsequent decades of life. Organomegaly is usually absent but respiratory muscle weakness was found in three of seven adults with AMD observed at the Mayo Clinic. In adults, the disease is slowly progressive and mimics other chronic myopathies. Electromyography shows an abnormal irritability of muscle fibers and myotonic discharges, without clinically detectable myotonia, in all cases. However, these findings in adults are less widely distributed and less intense than in the other cases and appear especially in trunk muscles. Microelectrode studies in an infantile case revealed myotonic discharges arising from single muscle fibers and normal neuromuscular transmission. The common histopathologic finding is a vacuolar myopathy with high glycogen content and a positive acid phosphatase reaction of many vacuoles. However, in adults with AMD, not all muscles display a vacuolar myopathy. At each age, a large proportion of the accumulated glycogen in muscle fibers is stored in membrane-bound spaces. Acidic mucosubstances accumulate in muscle in infantile and childhood but not in adult cases. Biochemical studies indicate AMD in all skeletal muscles in each group of cases. Other key glycolytic enzymes were present in normal amounts in each case. In children and adults, glycogen excess is found only in those muscles that show extensive histologic changes; in infants, glycogen excess is present in all muscles. Compensatory factors responsible for the milder expression of the syndrome in children and adults remain to be identified.
ASJC Scopus subject areas
- Clinical Neurology