Friday, May 29, 2009

Does Blood Type Affect ADHD?

This blog has often discussed the wide range of genetic influences on ADHD and related disorders. Some of the ADHD genes we have previously investigated include:

Additionally, some of these genes may work together in combo. For example, a combination of specific variations in the DAT1 gene and the DRD4 gene may associate with IQ and behavioral disorders as they relate to ADHD.

The main point of all of these examples was not to overwhelm anyone, but rather to highlight the intricate relationship between genetics and ADHD heritability.

Adding to this extensive list may be a new set of genes related to blood types and ADHD.

**For a quick synopsis of blood types, please consult the italicized paragraphs below. Otherwise you may skip to the next paragraph highlighting a new study on blood type and ADHD.

Human blood types are often classified by the "ABO" system. "A" and "B" refer to immune-regulating factors and play a major role in blood transfusions. These blood types are acquired from our parents and can come in dominant and recessive forms. Genes for blood type can be found on the 9th human chromosome.

They are the two main (or dominant) forms of immune-regulating blood factors. Additionally, A and B can be "codominant", that is an individual can have a mixture of the two. For these "codominant" individuals, their blood type is labeled "AB". If an individual has neither "A" nor "B", he or she is labeled as an "O".

In essence, if you have a specific letter(s), you can donate blood to individuals who share your same letters (there are actually other important factors and donor restrictions besides this, such as the "Rh factor", but for sake of simplicity, we will just discuss "ABO" for the moment). For example, a person with type "A" blood could donate to another person who has "A" or "AB" because both "A" and "AB" would recognize the "A" component. They could not donate to a "B" or an "O" blood type because these individuals' bodies would not be able to recognize the "A", resulting in a severe immuno-rejection problem.

An "O" could donate to and "A", a "B", an "AB", or another "O" (again, there are detailed exceptions to this generalization), because "O" does not have either of the "A" or "B" markers on it, so the recipient's body would not see anything "foreign" about this. This makes "O" carriers better candidates for blood donation. On the flip side, and individual with type "AB" could take blood from and "A", a "B", an "AB" or an "O" since their blood already recognizes the "markers". This makes AB candidates better recipients for blood.

In addition to an individual's blood type governing the blood transfusion process, blood types may also confer resistance or susceptibility to certain bodily dysfunctions or diseases. For example, type "A" individuals may be naturally more prone to cancers of the digestive system, and individuals with type "O" are more prone to cholera, plagues, or even malaria (interestingly, they may be more prone to be preferred targets of mosquitoes, compared to the other blood types).

Overview of an original study on ADHD and blood types:
Returning to our main discussion, it appears that certain blood types may also be related to an increased likelihood of childhood ADHD or related disorders. A Chinese study recently came out which sought to investigate whether certain blood types were actually more likely to be affiliated with ADHD. The results, while preliminary, should nevertheless pique some interest on the topic among professionals.

Here are some of the major highlights of the study:
  • Blood types (using the "ABO" format) were taken from 96 children and their parents, to determine the heritability patterns of blood types.
  • Both ADHD and non-ADHD children were observed in the study, and their blood types were broken down.
  • The study found that children who did have ADHD were more likely to have inherited either the "A" or "O" type blood from their parents.
  • Conversely, children who inherited the type "B" blood (which would include either the "B" or "AB" form) were less likely to be diagnosed with ADHD.

** A caveat concerning the findings and reproducibility of this study: It is important to note that the study population was relatively small, especially for a study of this magnitude which seeks to identify general trends between blood types and their relative association with co-existing disorders. Some blood types can be relatively rare, for example, in the United States, only around 10% of the population has type "B" blood and only about 15% has the "B" in any form (types B or AB). Although blood types vary extensively all over the world, certain types tend to predominate, which requires large populations to be studies to ensure all groups are sufficiently represented. Thus, small population studies can easily produce skewed results. Nevertheless, I personally believe this study was a good starting point.

**Blogger's personal notes/opinions on these findings:

I found this study to be interesting. Unfortunately, I could not read the whole article (the majority is in Chinese!), but the possibility of blood typing being related to ADHD would be a major breakthrough, if these results are able to be consistently replicated with larger population studies.

My first thought was that maybe some nearby gene related to ADHD might be influencing the blood type/ADHD connection, but no significant genes associated with ADHD exist on the 9th chromosome (at least to the best of my knowledge after conducting a search of OMIM for the term "ADHD", a national database which ties down diseases and disorders to known genetic regions). However, genes which are located far apart from each other, even on completely different chromosomes can also work in tandem, so genetic relationships between ADHD genes and blood type genes cannot be ruled out entirely.

Another option may be some type of indirect connection between blood type and ADHD. For example, the article notes that individuals who have the "O" or "A" blood type alleles are more prone to ADHD. Other sources note that individuals with type "O" are more prone to developing intestinal and gastric ulcers, and that individuals with type "A" are more prone to cancers of the digestive system (such as cancers of the esophagus, pancreas and stomach). This may signify that these blood types (compared to those who have "B" or "AB" blood) may be more prone to digestive problems.

Digestive disorders can result in poor nutrient absorption (we have discussed nutrient deficiencies in ADHD in number of previous posts), which may leave one more prone to ADHD symptoms. Additionally, digestive dysfunctions can actually lead to an increased likelihood of developing food allergies, as potential allergens are less likely to be broken down or "chewed up" than by a properly-functioning digestive system. Furthermore, we have also explored the possibility that acid accumulation can make its way into the brain regions and have an impact on neurological symptoms including ADHD-like behaviors. This was discussed in a recent post investigating the high prevalence of ADHD in children who suffer from frequent ear infections.

While these possibilities are strictly hypothetical at the moment I firmly believe that we should further explore the possibility of specific blood types as possible underlying causes or risk factors for developing ADHD.