Learning Disabilities May Often Be Due to Lower Intelligence: Robert Plomin of London’s Institute of Psychiatry analyzed 15,000 twins and found reading and math disabilities much more strongly linked in identical than fraternal twins. This is strong evidence of a genetic basis.  However, he states that, based upon his research, any specific isolated disabilities are probably environmentally induced since he found reading and math difficulties were usually linked to lower general intelligence. 9/10/03 New Scientist