Pompe disease, a lysosomal storage disease, is an autosomal recessive disease caused by deficiency of the acid alpha-glucosidase (GAA) enzyme which leads to the accumulation of toxic levels of glycogen in lysosomes. This impacts cell function in multiple tissues, with heart and skeletal muscles the most seriously affected. Classic infantile-onset manifests within the first few months after birth and is due to the complete or near complete deficiency of GAA. Symptoms include myopathy, feeding difficulties, and heart issues. If untreated, this form of Pompe disease is typically fatal before age 1 due to heart failure or respiratory complications. Non-classic infantile-onset typically appears before age 1 and manifests with delayed motor skills and progressive muscle weakness. It is due to a partial deficiency of GAA. Patients may have cardiomegaly, but this does not lead to heart failure. This form of the disease typically leads to serious breathing problems and is usually fatal by early childhood. Late-onset type may not manifest until later in childhood, adolescence, or adulthood. This milder form is less likely to involve the heart. Symptoms include progressive muscle weakness, which eventually impacts the muscles that control breathing. Cause of death is typically respiratory failure. This laboratory performs Sanger sequencing of the GAA gene.