A learning disability tends to be defined by IQ (IQ less than 75 or so), rather than anything else.
Thus, someone with a chromosomal disorder, or someone who was deprived of oxygen during birth, or someone who is just stupid because of genetics all have learning disabilities. They just have different forms of learning disability.
Is it just a difference of degrees? I mean both are cases of "factor outside of individuals control -> (extremely) low intelligence"