IRS1 and ganglioneuroma: Elevated fasting serum insulin levels may be an early indicator of skeletal muscle insulin resistance in this model and corresponded with increased IRS1 protein levels and a reduced ratio of Ser636/9 phosphorylated IRS1 to total IRS1 in the GN and TA muscles, as well as decreased Thr389 phosphorylated p70S6K in GN.