Subject: Shouldn't identical twins have approx. the same amount of hair?

I write you today, simply out of curiousity and a little frustration of the 
unknown.  I have identical twin girls (supposedly).  The hospital said they 
shared one placenta.  They will be three in June.  One of the girls has a full 
head of hair; whereas, her sister has very little hair.  In fact, she has lost 
hair.  It has not fallen out in chuncks, but I can tell by looking at previous 
pictures that she's lost hair.  Blood tests say, her thyroid is fine, she's not 
anemic, and she does not suffer from lead poisoning.  We are treating it as 
Alopecia.  I just find it odd that if they are identical, why would one have 
Alopecia, but not the other or why would they not have more similar hair?   Any 
thoughts?

Re: Shouldn't identical twins have approx. the same amount of hair?