A 10-year-old girl visits her physician's office because she has been complaining about being thirsty and having to go to the bathroom all the time. She has lost 15 pounds over the past 6 months and has been more irritable than usual, especially after meals. The girl's fasting blood glucose is 575m (reference range, < 100m ), her C-peptide is 0.5m (reference range, 0.8-3.1m ), and she has autoantibodies against glutamic acid decarboxylase and insulin. On the basis of these findings, a likely diagnosis for this girl is:
a. Hashimoto's thyroiditis.
b. acute glomerulonephritis.
c. type 1 diabetes.
d. progressive systemic sclerosis.