very thin maine coon

[sophie94]

Hello, everyone
Need a little advice.. My two year old maine coon in very thin- Extremely active, playing all the time with his DSH brother.
He weighs 16 lbs, but you can feel every bone in his back.
He was bred from parents who were both negative for CMYBP-C HCM DNA MUTATION. Never the less, he still had an ultrasound last summer becasue there was a very faint murmer (grade one, it turned out, but better safe than sorry)
He has had juvenile gingivitis also, but that seems to have resolved.
He eats fine also.
Could it be just a growth spurt? Any suggestions ?

I am taking him for another check up on Wednesday.