Glycogen debrancher deficiency is reproduced in muscle culture.

Muscle cultured from two adults with debrancher deficiency myopathy showed abnormal glycogen deposits by electron microscopy. Glycogen debranching activity was markedly decreased, but phosphorylase activity was normal. Lack of glycogen debranching activity in muscle cultures from debrancher-deficient patients contrasts with the presence of a fetal isoenzyme of phosphorylase in muscle cultured from patients with McArdle disease and suggests that the genetic control of the debranching enzyme does not change during muscle development.