A 10-year-old boy is brought to the physician because of a 12-month history of wetting the bed at night. He has had increased thirst and urinary frequency during this time. The episodes occur every 2-3 weeks and last 1-2 days. There is no bed-wetting between episodes. His parents divorced one year ago. He is at the 97th percentile for weight and 60th percentile for height. Laboratory studies show:
Serum glucose 80 mg/dL
Urine glucose Negative
Urine protein Negative
Urine specific gravity 1.015
Which of the following is the most likely explanation for these findings?
