CALCIUM KINETICS IN GLYCOGEN-STORAGE-DISEASE TYPE 1A

Glycogen storage disease type 1a (Von Gierke's disease) is one of the more common glycogen storage diseases (GSD). GSD 1a patients can have severe idiopathic osteopenia, often beginning at a young age. Since ca lcium tracer studies offer a sensitive probe of the bone microenvironm ent and of calcium deposition, kinetics might be disturbed in patients with GSD 1a. Plasma dilution kinetics obtained using the stable isoto pe Ca-42 are shown in this paper to be quite different between GSD 1a patients and age-matched controls. Comparison of kinetic parameters in these two populations is made using a new binding site model for desc ribing calcium dynamics at the plasma-bone interface. This model descr ibes reversible binding of calcium ions to postulated short-term and l one-term sites by a retention probability density function psi (t). Us ing this analysis, adult GSD subjects exhibited a significant decrease (P = 0.023) in the apparent half-life of a calcium ion on the longer- term site compared with controls. The general theory of calcium tracer dilution kinetics is then discussed in terms of a new model of short- term calcium homeostasis recently proposed by Bronner and Stein [5].