Presymptomatic late-onset Pompe disease identified by the dried blood spot test.

Pompe disease or glycogen storage disease type II is an autosomal recessive disorder caused by mutations in the GAA gene leading to muscle weakness. Here we describe a 15 years old presymptomatic patient with normal muscle MRI, unspecific muscle biopsy findings but abnormal acid maltase activity in a dried blood spot test. Sequencing the GAA-gene identified a heterozygous novel splice-site and a heterozygous previously described mutation. The case highlights the variability in clinical phenotype and difficulties to diagnose late-onset Pompe disease. Dried Blood Spot (DBS) might be the most sensitive tool to pick up mildly symptomatic patients.