Diabetes mellitus and glycogen storage disease type I (GSDI) may initially appear disparate in metabolic profile: one characterized by uncontrolled hyperglycaemia due to disturbed insulin function and the other by fasting hypoglycaemia caused by impaired gluconeogenesis and glycogenolysis. However, they share a remarkably similar pattern and progression of renal dysfunction. This may be, we suggest, due to a convergence of their metabolic sequelae in upregulation of flux through the pentose phosphate pathway. This pathway yields triose phosphate molecules, which are precursors of the lipid, diacylglycerol (DAG). DAG plays an important role in the intrarenal renin-angiotensin system via the protein kinase C pathway. GSDI may be an interesting model which helps to unravel further the contributions of the many, varied nephropathic influences in diabetes. Conversely patients with this rare disorders would have much to gain from the innovative and vastly greater body of research carried out in diabetes.