• If one sibling of a pair of identical twins (who share identical genes) has ADD, the other has 81% chance of having it. This number drops to only 29% for non-identical, or fraternal, twins.
• If one parent has ADD, the child has 60% chance of having it as well. If both parents have ADD, the probability goes up to 85-90%.
• Parents of ADD kids are 24 times as likely to have ADD themselves.

Little wonder that people are carrying out extensive searches to find genetic footprints of ADD. Earlier studies have already implicated specific gene sites, such as HLA (human leukocyte antigen), dopamine transporter gene, and dopamine receptor D₄ gene with ADHD.

The most recent study, published yesterday (June 23) online in Molecular Psychiatry, has identified hundreds of alterations in chunks (or segments) of genes, rather than in specific point sites, that occur more frequently in children with ADHD than in normal children.

The authors compared genomes of 335 ADHD kids and their families with 2000 unrelated non-ADHD kids, and found 222 such altered gene chunks, called “copy number variations” (CNVs), only in ADHD kids. Many of these CNVs have been previously identified with other neuro-developmental disorders such as autism and schizophrenia.

Read the original article for more details.