Definitions

The diagnosis of TS was established by lymphocyte chromosomal analysis in combination with the presence of typical clinical features. The nutritional status classification was performed using BMI, according to the cutoffs indicated by the World Health Organization (14). Thus, all participants were classified as overweight/obese (≥25 kg/m²) or lean (≥18.5 < 25kg/m²). Essential arterial hypertension was defined by SBP ≥130 mm Hg or DBP ≥85 mm Hg or taking antihypertensive medication with no identifiable cause. Metabolic syndrome was diagnosed using the International Diabetes Federation criteria, which requires the presence of (1) central obesity (defined as waist circumference ≥80 cm) plus any two of the following four factors: (2) fasting plasma glucose 5.6 mmol/L (100 mg/dL); (3) HDL-c level <1.29 mmol/L (<50 mg/dL); (4) TAGs ≥1.7 mmol/L (>150 mg/dL) or specific treatment for this; and (5) blood pressure ≥130/85 mm Hg or treatment of previously diagnosed hypertension (15). Subjects were defined as having impaired fasting glucose (IFG) if fasting plasma glucose concentration was from 5.6 mmol/L (100 mg/dL) to 6.9 mmol/L (125 mg/dL) and/or IGT if 2-h post–glucose plasma glucose level was ≥7.8–11.0 mmol/L (140–199 mg/dL, respectively) according to the diagnostic criteria from American Diabetes Association. Subjects were divided into two groups with (a) normal glucose tolerance (NGT) (IFG and IGT negative) and (b) with IFG and/or IGT positive.

To evaluate the degree of IR, several indexes derived from either fasting or OGTT-stimulated concentrations of glucose, insulin, and TAGs were used:

Homeostatic Model Assessment of Insulin Resistance Index (HOMA-IR) was calculated using the equation:

Quantitative Insulin Sensitivity Check Index was determined according to the following formula:

McAuley index was measured according to the formula:

Matsuda index was calculated according to the formula:

where MPG (mg/dL) is mean plasma glucose OGTT, and MSI (μIU/mL) is mean serum insulin during OGTT.

Belfiore index was calculated from changes in plasma glucose and serum insulin using the equation:

where AUC is the values of the area under curve insulin (μIU/mL) and glucose (mmol/L) concentrations in the course of OGTT, respectively.

The pancreatic β-cell function was evaluated using the formulas of Hovorka et al. with some modifications.

The HOMA-β index, which was calculated using the following equation:

The C-Peptide Index (CPI), which represents the ability of fasting glucose to stimulate pancreatic β-cell secretion (fasting pancreatic β-cell responsiveness), was determined according to the following formula:

The CPII index, which represents the ability of postprandial glucose to step up pancreatic β-cell secretion, was calculated by

According to different indices, the following thresholds defined IR state among study and reference group subjects: HOMA-IR ≥ 2.5, QUICKI ≤0.339, McAuley index ≤ 5.8, Matsuda index ≤ 4.6, and Belfiore index ≥1.23 (16–18).