Endocrine Abstracts (2003) 5 P97

Altered insulin sensitivity and secretion in sotos syndrome

S Nag1, SMA Bennett2, J Gerrard2, M Walker2 & S Ball1

1Department of Endocrinology, University of Newcastle, Newcastle upon Tyne; 2Department of Diabetes and Metabolism, University of Newcastle, Newcastle upon Tyne.

Background: Sotos syndrome is an uncommon condition characterised by rapid growth, large body size and acromegaloid facies.There is limited data on metabolic abnormalities in Sotos syndrome.
Aims: We investigated insulin sensitivity and secretion rates in a 22 year old girl with Sotos syndrome, prompted by the observation of a flat glucose response after an oral glucose challenge.
Methods: Glucose tolerance was assessed with a 75g 2-h oral glucose tolerance test (OGTT), with paired samples for plasma glucose and insulin measured every 30-min. Insulin sensitivity was assessed during a 150-min euglycaemic hyperinsulinaemic clamp.Insulin secretion rates (ISR) were calculated from C-peptide kinetics during a stepped glucose infusion over 160-min.
Results: The subject's BMI was 30.02 kg/m2.Waist: Hip ratio was 0.87. Plasma glucose values during the OGTT were 4.4, 4.8, 2.3, 3.6 and 3.3 mmol/l. Corresponding insulin levels were 4.2, 88.2, 16.2, 19.3 and 7.4 mU/L respectively.Insulin sensitivity, expressed as the glucose infusion rate [M value] was 8.01mg/kg/min. The ISR at glucose infusion rates of 2, 4, 6 and 8 mg/kg/min were 215,415,661,753 pmol/min respectively. When plotted against prevailing glucose concentrations, a leftward shift in the ISR/glucose dose-response curve was noted.
Conclusions: The flat response to the OGTT is suggestive of enhanced insulin sensitivity with an increase in (first phase) insulin secretion. This is confirmed during the clamp and increased insulin secretion is demonstrated during the stepped glucose infusion. The left shift in ISR/glucose curve suggests that pancreatic β cells respond to small increments in plasma glucose. The converse is noted in subjects with glucokinase mutations where the ISR/glucose curve is markedly shifted to the right.
The significance of the lack of insulin resistance despite the obesity in the subject and the enhanced beta cell responsiveness is uncertain. More studies are required to quantify these metabolic abnormalities further.

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