Late-onset Pompe Disease: A Diagnostic Challenge

Pompe disease is an autosomal recessive, lysosomal storage disorder wherein affected individuals are deficient in the lysosomal enzyme acid alpha-glucosidase (acid maltase). Here, we describe a case of a 2-year-old male child, who initially presented at the age of 16 months with complaints of difficulty in walking without support associated with frequent falls. On follow-up after 6 months, progressive deterioration in clinical signs was noted. His serum Creatine Phosphokinase (CPK) levels were 2067 U/L. Given the progressive nature of the condition, we ruled out congenital muscular disorder, metabolic and endocrine myopathy. A clinical exome sequence was ordered to check for the myopathy panels. The results revealed a homozygous missense variation in exon 11 of the Acid Alpha Glucosidase (GAA) gene. His alpha-glucosidase levels were 0.8 nmol/hr/mg, which was indicative of the deficient activity of the enzyme in the leukocytes.