Dietary treatment in adult-onset type II glycogenosis.

Eight patients with adult-onset type II glycogenosis (GSD II), all carrying the IVS1-13T<G mutation, were treated with high-protein isocaloric diet for 3 years. We evaluated the usefulness of this approach through the assessment of the skeletal muscles (by manual muscle testing, quantitative isokinetic exercise, and muscle MRI) and the respiratory function (by spirometry). Three patients with mild or moderate disease severity refused the diet and were still monitored for comparison: they showed clinical (2 patients) or clinicoradiological (1 patient) progression of muscle weakness, while respiratory function remained unchanged. Among the patients accepting the dietary treatment, muscle strength remained unchanged, as did the degree of fatty infiltration and atrophy as assessed by muscle MRI; respiratory function worsened in 2/5 patients with severe baseline respiratory dysfunction. High-protein diet may stabilize disease progression at the skeletal muscles, but does not produce significant clinical improvements; moreover, the usefulness of this approach in patients with severe respiratory disease seems questionable.