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A high percentage of patients with CF also present with IGT. This increases with age and is more common among patients homozygous for the deltaF508 mutation and is not related to clinical status. Alterations in the kinetics of insulin secretion play an important role in the appearance of IGT and CF. We suggest that the OGTT is a more sensitive method than IVGTT for identifying early alterations in CF-related diabetes mellitus.

6 girls, aged 4–16 years, with acanthosis nigricans and hirsutism were studied. Fasting and postglucose hyperinsulinism was present in the 5 older girls. In the youngest, a transitory diabetes with hyperinsulinism was induced by a cortisone therapy for hepatitis. Insulin resistance, suggested by the failure to significantly decrease blood glucose after insulin injection (0.1 U/kg), was demonstrated in three steps: (1) Patient plasma failed to bind ¹²⁵I-insulin after a 5-day incubation followed by precipitation by antihuman globulin serum. (2) Specific ¹²⁵I-insulin binding to rat liver membranes was identical in the presence of patient plasma and control plasma. (3) Specific ¹²⁵I-insulin binding to the erythrocytes of the 6 patients (3.5–7.0%) was significantly lower (p < 0.01) than in controls (4.5–19.5%). Moreover, the significant correlation present in controls between total binding and reticulocyte counts (r = 0.824, p < 0.001) was absent in the patients. These data demonstrate further that, in the juvenile type of acanthosis nigricans, insulin resistance which may precede hyperinsulinism is not related to anti-insulin antibodies nor to antireceptor antibodies, but results from a primary defect of insulin receptors.

Specific insulin binding to erythrocytes was studied in 5 infants with nesidioblastosis and in 15 controls. A close correlation was found between the binding and the reticulocyte count in controls. According to the number of reticulocytes in their blood, 2 patients had increased binding, related to an increased number of high-affinity sites. In 3 patients studied after therapy, the binding was similar to controls, the affinity of high-affinity sites being decreased when their number remained unchanged.

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