Diabetes Insipidus, Possible Precocious Puberty

My son was diagnosed with DI in 2008.  He takes DDAVP twice a day and with the exception of the days a pill gets forgotten, he is symptom free and thriving.  For a while after diagnosis, he wasn't growing very much or gaining much weight.  Just after he turned 9 in July 2009, we noticed the early signs of puberty.  At the present time, it seems to be progressing kind of rapidly.  His voice has deepened considerably in the past few months, he has quite a bit of pubic hair and leg hair but not underarm hair.  He has a fuzzy upper lip, also.  He actually has grown 1.5 inches in the past six months and gained five pounds, but he is still on the small side.  (51 inches and 57 pounds).  He has an appointment with his Endo on April 6th, but I like to be armed with info when I go.  I know 9 isn't crazy early for puberty to start but considering the Central DI, I'm wondering if the two are related.  Any thoughts?