GAA and disorder of glycogen metabolism: Pathogenic variants in GAA cause a glycogen storage disorder called Pompe disease.32,33 In silico scores suggest this variant is unlikely to be deleterious (PhyloP < 0; CADD = 5.9), but following contact with the clinical team, biochemical assays confirmed marked deficiency of GAA enzymatic activity in the participant and hence a diagnosis of Pompe disease.