Lysosomal glycogen storage disease with normal acid maltase

TLDR

Two unrelated 16‑year‑old boys presented with mental retardation, cardiomegaly, proximal myopathy, and hepatomegaly, yet the underlying glycogen storage disorder remains unexplained. Muscle biopsies revealed lysosomal glycogen accumulation characteristic of acid maltase deficiency. Muscle glycogen was elevated but structurally normal, and acid α‑glucosidase activity as well as other glycogen‑metabolism enzymes were within normal limits.

Abstract

Two unrelated 16-year-old boys had mental retardation, cardiomegaly, and proximal myopathy. One also had hepatomegaly. Histochemistry and electronmicroscopy of muscle biopsies showed lysosomal glycogen storage resembling acid maltase deficiency. Biochemical studies of skeletal muscle showed increased content of glycogen of normal structure; acid a-glucosidase activity in both urine and muscle was normal. Other enzymes of glycogen metabolism were also normal. The cause of this apparently generalized glycogenosis with no demonstrable enzyme defect is unknown.