No body fat in my baby !!!!!!!!!!!

I need to know if there is a disease out there in which a baby is born healthy , but the body does not produce any body fat ----
My son is 3 years old , born healthy , but has not had any body fat on him since the day he was born ----- He was diagnosed as failing to thrive , and was tested for every disease that you can think of pertaining to slow weight gain , and every single test came back negative ----- He is very tall for his age , very active , and just LOVES to eat !!!!!!!!!!! Also , his height is in the 95 percentile , and weight has climbed from the 5 percentile , which took me about 2 years to get his weight up . I can't help but wonder if his doctors are missing something , like a rare disease that they have not thought of , because if you look at him , his body has no fat on it , his legs are long and skinny , and his arms are skinny too , but other than that , he is your normal , average 3 year old who eats ALOT ------- I just need to know if there is a disease out there that describes my son's strange body !!!!!!!!!!!!!!!!!!! Please let me know !!!!!!!!!!!!!!!!

Hi,

My daughter is also very slim at 2 years old (only about 22 pounds) even though she eats well, while my son was a chubby baby. He has now become a very slim, yet extremely active, healthy 6 year old who eats very well. Kids are born one way, and then may change later, or sometimes they are just slim naturally right from birth and stay that way. Either way, I caution you not to worry or over-react as long as he/she is learning mentally and reaching all the normal milestones (walking, running, using motor skills, talking, etc.) as any other child does. Even if mom and dad were chubby or tall as babies, sometimes our kids take on the genes from other family members who were slim or short. Keep an eye on your child's overall development (not just the physical), and go from there. If you get stressed out over the matter, chances are your child will too. Pay attention to your mother's intuition, but try not to let it make you go overboard prematurely or unnecessarily.

I know that there are actually diseases though where it is difficult for a child to keep weight on its body and I forget completely right now what the name of it is but I know that it affects children greatly and it's hard for them to get into adulthood. They have to eat a ton to keep themselves at just a normal weight. Again, I don't remember the name of it but sometimes it's an issue like that. I wonder if that's what the poster's child has. Does anyone know the name?