A study was designed to address this question, whether iatrogenic peripheral hyperinsulinemia or hyperglycemia is mainly responsible for reduced muscle insulin sensitivity in T1D (146) by examining people without diabetes (euglycemia, normoinsulinemia), with glucokinase maturity–onset diabetes of the young (hyperglycemia, normoinsulinemia), and with overt T1D (hyperglycemia, hyperinsulinemia). This evidence concerns the gene GCK and Hyperglycemia.