if ADHD is genetic, why isn’t there a blood test for it?
In: Chemistry
* Because they only think it is genetic because it runs in families, and they have no idea which genes may or may not cause it.
* It might not be one gene, but a combination of several
* Other, non genetic things can also cause it, like head injuries.
You can notice something is genetic long before you can identify _what_ gene, geneS, or specific combination of genes (that individually do nothing significant), or *epigenetic* modifications (distinct from genes), or *combination* of genetics and epigenetics leads to conditions. Add to that, you can’t just compare two individuals, one with and one without, because there will also be *thousands* of other differences to mix in– you would be aiming to identify the cause behind *one* of these differences, independently, *somehow.*
Biology is fun, but it’s a very messy science and it’s often difficult trying to explain things definitively.
Noticing ADHD/autistic/other-condition parents more frequently have kids with a similar condition though, or related observations? Easy.
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If it is genetic, it is caused by a combination of genes, and we don’t really know which ones. If it were just one gene, it would be really easy to determine, and also would have been acted on by selection long ago. Most complex traits (intelligence, attention span) and even many simple ones (height) are caused by many different genes acting in different ways. All the easy genetic wins have already happened, basically; if one gene did something unambigously good, it lived, and all the others died out. We’re now left with genes that point in different directions for different things, so selection on them is difficult.
ADHD is assumed to be genetic because we can see it seems to run in families but we don’t know the exact genes in order to test for it. The environment likely plays a role too, making it harder to predict who will end up with ADHD symptoms.
There’s a genetic component but that doesn’t mean they have identified the gene and it doesn’t mean that someone without adhd in their family doesn’t have it.
It’s not entirely genetic is also highly environmentally influenced. I recommend the book scattered and pretty much anything else is ever written by Gabor Maté. Bipolar disorder is, if anything, more genetically irritable and we have no blood test for that. In fact, we don’t have a blood test for any DSM diagnosis to my knowledge that doesn’t mean they’re not real or genetic. There are many non-genetic diseases for which we don’t have a blood test that doesn’t make them any less real.
Surely not all hereditary conditions can be blood tested. Me and my brother have Con/Rod dystrophy and it’s genetic but we’re the only ones who have the condition (it’s recessive and fairly rare) but you can blood test for blindness… as far as I know.
If eye colour is genetic, why isn’t there a blood test for it?
Things can be genetic without having blood markers.
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