INSULIN RESISTANCE IN MYOTONIC-DYSTROPHY

The aim of the present study was to obtain a comprehensive picture of the rate of insulin secretion and of tissue sensitivity to the endogenous hormone in myotonic dystrophy patients (MyD). The minimal model approach was utilized for the analysis of frequently sampled intravenous glucose tolerance test data (FSIGT). This method provided the characteristic parameters: S(I), insulin sensitivity index; S(G) fractional glucose disappearance independent of dynamic insulin; n, fractional insulin clearance; PHI-1 and PHI-2 first and second phase insulin delivery sensitivities to glucose stimulation. In MyD patients S(I) was reduced (p < 0.01) by 71% to 1.4 +/- 0.3 x 10(-4) min-1/(mu-U/ml), whereas in controls it was 4.85 +/- 0.77; S(G) was within the normal range: 0.044 +/- 0.012 min-1 in MyD patients and 0.036 +/- 0.017 min-1 in controls; PHI-1 increased in MyD patients (7.4 +/- 1.3 min (mu-U/ml)/(mg/dl) versus 4.1 +/- 1.2 in controls); PHI-2 increased in MyD patients (126 +/- 47 x 10(4) min-2/(mu-U/ml)/(mg/dl) versus 17 +/- 6 in controls; p < 0.05). MyD patients showed a normal tolerance with the glucose disappearance constant, K(G) within the normal range: 2.75 versus 2.62% min-1 in controls. In MyD patients insulin resistance was associated with a higher than normal insulin delivery for both secretory phases, although the second phase was responsable for releasing a greater amount of hormone. In conclusion MyD patients try to compensate for overall insulin resistance by a more marked pancreatic response.