A five-year-old boy with late-infantile (juvenile) form of acid maltase deficiency is presented. His symptoms were restricted to skeletal muscle. There is commonly a correlation between the amount of residual acid maltase activity and the severity of the clinical picture. Although the residual enzyme level was very low in our patient, no progression of his neurological findings have been observed during the follow-up period of two years.

Keywords: acid maltase deficiency, glycogen storage diseases, late-infantile form