Muscle [31P] NMR spectra of a GSD IV affected cat and a normal littermate. Panel A shows the spectrum collected from the triceps surae of a normal male cat and panel B shows that collected from his GSD IV affected male littermate, each at 18 weeks of age. Panel C shows the spectrum collected from the affected cat at 23 weeks of age. Spectral peaks representative of inorganic phosphate, phosphocreatine, and ATP labeled in the γ, α, and β phosphate positions, are indicated by Pi, PCr, γ, α, and β, respectively. PME and PDE indicate peaks of phosphomono- and phosphodiesters, respectively.