Insulin sensitivity and early-phase insulin secretion in normoglycemic Huntington's disease patients

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an expanded CAG repeat in exon 1 of the HTT gene. There is increasing evidence pointing towards an involvement of the endocrine system in HD. Recent studies, investigating the increased risk of diabetes mellitus and impaired insulin sensitivity and secretion in HD patients, led to contradictory results.

To investigate glucose homeostasis in HD.

Twenty-eight consecutive patients with HD and 28 healthy controls were matched for age, sex, and BMI. Diagnosis of HD was confirmed genetically. Clinical tools for assessment were the Unified Huntington's Disease Rating Scale (UHDRS) motor section and the Total Function Capacity (TFC). Basal metabolic and endocrine investigations and a 2-hour 75-g oGTT were performed. We used the homeostasis model assessment of insulin resistance (HOMA-IR) as index of insulin sensitivity and the insulinogenic index to assess insulin secretion.

HD patients did not differ from the controls with respect to fasting plasma glucose, insulin sensitivity and secretion. CAG expansion size, disease stage and duration, or BMI did not influence HOMA-IR and insulinogenic index. Patients showed lower serum glucose (-19%) and insulin levels (-48%) at 30 min and higher serum insulin levels at 90 (+132%) and 120 min (+380%).

Our data do not support an increased risk of diabetes among HD patients although they show glucose regulation abnormalities with a flat glucose curve and delayed insulin peak after oral glucose load.