Here is an excellent definition of what a learning disability is and some characteristics:
A child with a learning disability cannot try harder, pay closer attention, or improve motivation on their own; they need help to learn how to do those things. A learning disability, or learning disorder, is not a problem with intelligence. Learning disorders are caused by a difference in the brain that affects how information is received, processed, or communicated. Children and adults with learning disabilities have trouble processing sensory information because they see, hear, and understand things differently.
Taking this into perspective it seems that children are not taught to have learning disabilities but may learn behaviors that cause them to not function well in school. A learning disability occurs because of an imbalance of communication somewhere in the brain. The only way that I can see a learning disability may be directly correlated to substance abuse is if a mother was using drugs while pregnant and damage was caused to the fetus.
Another website you can visit to get information on psychological journals is the American Psychological Association website listed below.