attery-Revised and scored at or below the 16th percentile on the Spelling subtest of the Wide Range Achievement Test Revised or the Woodcock-Johnson Psycho-Educational Battery-Revised Spelling subtest, and scored less than 17 on the Auditory Analysis Test. Children were classified with higher level RD if they displayed deficits in basic reading skills or in reading comprehension. One hundred and twenty-seven children with RD were selected for the study. Sixty-eight children had both ADHD and RD.
All children were given the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) and the Wide Range Assessment of Memory and Learning (WRAML) was used to assess verbal and visual memory. The General Memory Index from WRAML reflects overall memory abilities. The results of this study showed that the IQs of children with ADHD represent the entire spectrum from giftedness to mental disability. Children with comorbid ADHD and RD scored similarly, as did those with RD alone, showing that ADHD does not have any particular affect on a child's IQ. The IQs of children with ADHD fall within the normal range for children without the disorder.
The causes of ADHD are not fully known, although there seems to be a genetic component since ADHD appears to run in families and children with an ADHD parent or sibling are more likely to develop ADHD themselves (Ford-Martin, 1999). Other causes under investigation are exposure in utero to poor maternal nutrition, viral infections and maternal substance abuse. In early childhood, exposure to lead, and other toxins can produce ADHD-like symptoms, as can traumatic brain injury and neurological disorders. The mechanism underlying ADHD appears to be an imbalance in certain neurotransmitters.
Recent research suggests that children with ADHD generally have impaired functioning in the cortical and subcortical regions of the brain (Ballard et al, 1997). The cortical region is related to lear...