Genetics of ADHD
ByOne of my readers forwarded this question: “what are the chances that I will pass ADHD on to my kids?”
This is a great question, which goes right to the heart of the genetics of ADD or ADHD.
As I explained in a previous article about the cause of ADHD, ADD and ADHD are very ‘heritable’, meaning that it is a very genetic disorder.
Many twin and family studies have been done on this topic. While each study yielded slightly different results, here is a summary:
If a person has ADHD, then:
- an identical twin has a 78-92% chance of having ADHD as well.
- 25-35% of siblings have ADHD as well.
- 15-20% of the mothers have ADHD as well.
- 25-30% of the fathers have ADHD as well.
If a parent has ADHD, there is a 20-54% chance that his/her child will get ADHD as well.
If both parents have ADHD – well, I don’t know of any research statistics, but let’s just say that there is a very high chance of a child having ADHD as well.
So, to answer the specific question – if you have ADHD, and you plan to have kids, each child has about a 20-54% chance of having ADD or ADHD.
Hi,
It seems when kids do inherit the ‘ ADHD genes ‘ , they get it far worse than we did. A friend of mine has this theory that when a gene mutates the defect becomes bigger. I wish this was true with our good genes.
How do you explain this phenomenem
Allan
Allan – thank you for your comment.
There is a genetic theory called ‘anticipation’.
This refers to the fact that certain genetic disorders do worsen when they pass from one generation to the next.
That said, I do not believe that ADHD has been described as displaying ‘genetic anticipation’. But if you want to read more, then this is the term to look for.
In my clinical experience, I have seen ADHD getting worse when both parents have it, or if one parent has it, and the other has a family history of it.
Thanks again for reading and commenting.
Dr. Kenny
Dear Dr Kenny
I suspect that in the long run, ADHD will prove to be highly polygenic despite the tight focus on dopamine receptor and transporter genes. Recent work on the genetics of Bipolar Disorder and Schizophrenia by Pamela Sklar is pointing to more fundamental issues (both of these disorders have links to ADHD) .
The work by Martin Pall on NO/ONO (nitric oxide/peroxynitrite) metabolic problems may also shed light.
If ADHD is highly polygenic, and as several have asserted, that assortive mating is prevalent, then one would expect more double recessives to appear and traits to strengthen.
So Calochilus what your saying is in theory the increased symptoms is not because the child is raised viewing these symptoms as a normality and thus increasing the symptoms the child displays in addition to his/her own add but merely because these genes stack to create stronger symptoms. From what I know in genetics(very limited) I see that most genes take the predominate feature of the two but to have these two combine is a different view that I have not considered yet. Are there studies that have focused on this specifically that are available to the public?
Hi, none of that information has any direct genetic basis and could as easily a result of the environment. You’d need statistics on non-identical twins and adoption studies as well for that to have any relevance, ADD is just behaviourally inherited based on what you said
Much behaviour is learned, not inherited.
If you want statistics, see the work of Hay and Levy, enough there to keep you reading for some time. Overall conclusion, ADHD heritabilty is between 0.8 and 0.9
See http://www.cognitivepsychologyarena.com/attention-genes-and-adhd-9781841692678
The learned aspects are more related to oppositional defiance and conduct disorder according to Barkley.
However, a complicating factor that is being more widely recognised is the impact of epigenetics.
See http://www.epidna.com/showabstract.php?pmid=17915085
also http://eprints.qut.edu.au/13794/ where epigenetics is explored in relation to PTSD. Martin Pall’s work has shown possible links in physiological mechanisms relating to this.
See also http://www3.interscience.wiley.com/journal/120120678/abstract?CRETRY=1&SRETRY=0
See also http://www.mdconsult.com/das/article/body/180511137-2/jorg=journal&source=&sp=N&sid=0/N/721514/1.html?issn=
Happy reading
Follow up question:
My brother has ADHD (at the higher end of the scale) , my partner I do not, what is the chance of us having a child with ADHD?
Thanks
Hi,
If I understand correctly – you’re wondering what the risk of having ADHD in your child if your brother has ADHD. I don’t know an exact answer to that… The general population risk is 5%. With someone in the family – it would be up a little- but with an uncle – probably not that much.
Dr. Kenny
Hi Lizzie
Your problems come about when trying to reconcile the DSM4 diagnostic criteria which are categorical (ie. you either have ADHD or you don’t), with the reality of ADHD which is a dimensional problem ( meaning that ADHD issues or traits can vary from immeasurable to devastating).
Not only are ADHD issues dimensional, but there are several, more or less, independent domains such as attention, distractability, impulsivity, together with various comorbid (occurring at the same time) but possibly distinct issues such as dyspraxias, central auditory processing issues and visual processing issues (the dyslexias and Irlen Syndrome, etc). If you want to get a handle (no pun intended) on this stuff, you should read John Ratey and Catherine Johnson, “Shadow Syndromes”
The reality is that DSM4 deals poorly with women with ADHD as the diagnostic statistics show. One in five children diagnosed with ADHD are girls. In adulthood, the ratio is one to one. This tells me that DSM4 is missing many girls with the ADHD traits which are of minimal impact in childhood but greater impact in adulthood. (Is this because girls have greater verbal skills which mature earlier than boys?)
The other reality is that the small proportion of boys with severe behavioural issues have dominated stereotypes of ADHD. 80% of ADHD kids are remarkable by their invisibility to the bulk of the population, the daydreamers, the “Walter Mittys” of this world. The others who are not un-remarked but are un-acknowledged as ADHD are the artists, musicians, mathematicians, entrepreneurs, inventors etc. who have a strong risk-taking streak in an intellectual sense.
Given that you have a brother with well defined ADHD, my suspicions are that you will have ADHD traits which are a minor impediment to your progress. I also firmly believe that assortative mating is common and the chances are (in my mind) that your boyfriend will also have minor ADHD traits (which may be complementary to yours)
Jump in, take the plunge, your children might well include the next Albert Einstein or Pablo Picasso.