Insulin Resistance Is an Intrinsic Defect Independent of Fat Mass in Women with Turner’s Syndrome

BACKGROUND/AIMS: Turner's syndrome (TS) is associated with increased insulin resistance and adiposity, which might be associated with type 2 diabetes in later life. We aimed to determine whether the defect in insulin sensitivity is a primary intrinsic defect in TS or dependent on variation in body composition. METHODS: Sixteen women with TS not on growth hormone replacement but receiving oestrogen replacement therapy age (mean +/- SD): 30.2 +/- 8.5 years; height-corrected fat-free mass: 26.1 +/- 3.1 kg/height and a control group of 16 normal healthy women (age: 30.1 +/- 8.2 years; height-corrected fat-free mass: 25.9 +/- 2.4 kg/height) were studied. Fasting blood samples were obtained for measurement of glucose, insulin, IGF-I, IGFBP-1, IGFBP-3 and lipid levels. The hyperinsulinaemic euglycaemic clamp was performed to assess peripheral insulin sensitivity (M value), and the Homeostasis Model Assessment (HOMA-S) was used to estimate fasting insulin sensitivity. Body composition was assessed using a dual-energy X-ray absorptiometry scan. RESULTS: Fasting insulin sensitivity (HOMA-S 103.2 +/- 78.6 vs. 193.9 +/- 93.5, p = 0.006) was lower in TS subjects compared to controls as was whole-body insulin sensitivity (M value 2.9 +/- 1.9 vs. 5.5 +/- 2.6 mg/kg/min, p = 0.003). In a multiple regression analysis the Turner karyotype was significantly related to insulin sensitivity (p = 0.008) independent of any differences in fat-free mass and percent whole-body fat mass. CONCLUSION: The increased insulin resistance in women with TS is independent of measures of body composition and may represent an intrinsic defect related to their chromosomal abnormality.