Acid maltase deficiency (Glycogen Storage Disease Type II, GSD II) is caused by a deficiency of ∝-1,4-glucosidase, resulting in intralysosomal storage of glycogen in almost all tissues. The spectrum of clinical symptoms is heterogeneous with regard to age of onset, organ involvement and prognosis. Subjects beyond 2 years of age present typically with a progressive myopathy, predominantly of lower limb and respiratory muscles. We showed recently that the myopathy is due to increased whole body protein breakdown rather than decreased whole body protein synthesis. Dieatry treatment has however remained difficult, despite the fact that in 1983 Slonim reported a high-protein diet to improve the myopathy in a child with GSD II. First a high-protein diet is difficult to take and secondly often results in considerable weight gain, which impaires respiratory function further. L-alanine might be an alternative dietary approach in these subjects. As the key aminoacid in gluconeogenesis, its production is also regulated by protein breakdown. By increasing the alanine intake we might find a sparing effect on muscle aminoacids, which would be available for protein synthesis.

We studied glucose and protein kinetics by stable isotope techniques together with resting energy expenditure (REE) in 7 subjects with GSD II (age 15-62 years, mean 35 years) and 12 healthy volunteers (age 21-54 years, mean 32 years). 5 of the subjects and 5 of the volunteers were then put on a 4 week supplementation with L-alanine (0,143g/kg/day) and restudied in the same manner as before. REE (kcal/kgLBM/day) in GSD II subjects was 26.64(16.2-43.2) before alanine and 21.77 (11.6-31.3) (p<0.05) after respectively, while there was no difference in the control subjects before and after alanine (18.3/ 17.9). Leucine turnover (protein breakdown) in GSD II changed from 130.6 to 112.1 μmol/kg/h after alanine (p<0.05). There were no changes in the control subjects (115.4 and 117,3μmol/kg/h).L-alanine reduces protein breakdown and energy expenditure in subjects with GSD II. It might also be of benefit for subjects suffering from other forms of myopathy.