Impaired insulin sensitivity and secretion in normoglycemic patients with spinocerebellar ataxia type 1

We have recently shown an impairment in insulin sensitivity and insulin secretion in normoglycemic patients with Huntington disease (HD). To investigate whether such observations are HD-specific or may be common to other polyglutamine diseases, glucose homeostasis was studied in 12 unrelated, untreated normoglycemic patients with spinocerebellar ataxia type 1 (SCA1), another entity from the family of polyglutamine diseases, and 24 healthy, matched controls. Metabolic investigations included (a) glucose tolerance assessment on the basis of glucose curve during oral glucose challenge; (b) insulin sensitivity assessment by the homeostasis model assessment (HOMA) and the euglycemic insulin clamp (M value); and (c) insulin secretion by acute insulin response (AIR) and insulinogenic index. The evaluation of insulin sensitivity demonstrated higher HOMA-insulin resistance indices, and lower M values (P < 0.001 and P < 0.05, respectively), while both the AIR and the insulinogenic index were lower in patients with SCA1 compared to controls (P < 0.001 and P < 0.05, respectively). Our data suggested an impairment in insulin secretion capacity, as well as simultaneous decrease in insulin sensitivity, with an increase in insulin resistance level in patients with SCA1.