Autosomal recessive causes of LV wall thickening include glycogen storage disease (GSD) type II [caused by acid α-1,4-glycosidase (GAA) deficiency], GSD IIIA (caused by amylo-1,6-glucosidade/debranching enzyme deficiency), and Friedreich’s ataxia caused by expansions—GAA triplet repeats—in the frataxin gene. The gene discussed is FXN; the disease is glycogen storage disease II.