Disorder of bones in hands

I have three children. The first two - a boy and a girl - have a disorder of the bones in their hands. That is, I believe the metacarpal attached to the finger bone is abnormally short. The result is that they do not have knuckles at the base of the respective fingers. My son has three knuckles missing on one hand and two on the other. My daughter has one missing on one hand and two on the other. It seems to affect the little finger first, i.e. both children have the knuckle to their index fingers.

I'm contacting you as an interested parent, rather than a concerned one, as both children are generally healthy and are not physically handicapped by the problem. I would be interested to know if this syndrome has a name? Also, is it connected to any other problems as my son has a learning problem? My third child - a boy - is not affected.