Thinking about Aspergers and genetics..

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Hi all

I'm thinking about if I carry the "gene" for Aspergers Syndrome.
I've got two siblings with Aspergers (same mother and father for sister, same mother different father for brother) and I'm curious if later on in life if I have children, would they have Aspergers. I am neurotypical, which is odd, because my siblings have aspergers and I dont, which I feel doesn't make sense. My mother doesn't have aspergers, and I don't know about my father. But with my siblings, I think that it may "run" on my mothers side.

Any one got any ideas on how to figure this out?

(Thread moved from News & Current events to Autism discussion)

Genetics are complicated. I don't know how much you know, so I'm going to presume total ignorance- sorry if I patronise you.

Think of your genes as being like the Bible. You have two slightly different versions of the Bible- the New International and the King James, for example. Sometimes the verses (genes) are the same in each version, in that case fine, we read that. Sometimes they are different, in which case one "dominates" the other and you ignore the other one. Hypothetically, you have one copy of the Asperger's gene, then it gets ignored and the other gene is read. You don't have Asperger's unless you have two copies (I must stress, this is very hypothetical and simplistic- more later).

However, when you create sex cells (sperm or eggs) the pages are torn out of each copy and mixed around a bit, and then the sex cell only gets one mixed up Bible, not two (though it will have every verse, just some will be NIV and some KJV). Then that cell meets with your partner's sex cell and they put their mixed up Bibles together. That means that some conditions that don't show for several generations can pop up later when they meet another copy of the gene.

Let's assume that your mother has one copy of the Asperger's gene (hypothetically) and the same is true for your father and step father. You are your siblings each had a 1 in 4 chances of having two Asperger's genes. You got at least one non-Asperger gene. There is a 1 in 3 chance that you have no gene for Asperger's, and a 2 in 3 chance that you are carrying a recessive gene like your mother and father. If you mate with someone who also has a recessive gene for Asperger's, then you will have a 1 in 4 chance of a child with Asperger's. This is how diseases like cystic fibrosis, Tay Sachs and sickle cell have survived the cruel hand of natural selection.

However... most of the time, genes don't work in such a simple way. A condition like Asperger's can be caused by multiple genes. It could be caused by multiple genes, but with some of those genes only functioning if certain other genes are present (like genes for extra hormone production). It could be largely environmental, or largely caused by conditions in the womb. Studies seem to show that whilst there is a genetic element, environmental conditions and pre-natal conditions also play a part. For this reason, unlike cystic fibrosis etc., there is no known "Asperger's gene", and consequently no genetic screening.

http://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat

I was thinking about that. What would be useful if we could choose a series of genetic markers for specific chromosomes that have easily identifiable phenotypes and look for a correlation with AS. I was also looking at distribution charts and there does seem a prevalence in Scandinavian populations and there decedents (including us Brits) and US population (esp Minnesota) autism rates even turkey.

It would be interesting to compare African American/European rates against those in Africa if accurate data was present also north African against sub Saharan. Also Native Eskimo/Sami and Nenets to see if its more prevalent in colder climates (ie possible selection bias in these conditions (it gives an advantage to survival?)

The one thing that's hard to explain is Japan. Does anyone know what happened to Japan around the last ice age or before? Or where the Japanese came from originally?

Not everything is down to what we can make out with a micro-scope.

If we can’t find the answers to human ailments conditions or what not, then it must be genetics, some smart scientist will unravel the cause later.
Autism has nothing to do with genetics. We, mankind are an ignorant lot, we seem to have this notion that if we don’t have a solution to the problem then whatever we say after this conclusion is just so.

I can’t repeat enough, we do not know how the mind works. There is more to the mind than matter.
If we think we know everything at this point in our evolution, then we are in serious trouble.
Just because a scientist has an answer, doesn’t mean to say it’s the right one.
Up until the late 70s, autistic Savants were called idiots by the experts.
The problem with scientist and there discovery’s (Genetics for example) is it’s only put to use to benefit someone’s pocket.
The race is on to unlock the aging gene; a ten million dollar prize is up for grabs.

What worry s me about the future is the fact we are discovering more and more useful ideas like genetics that can help all of mankind, but only if you can afford it.
I’m sorry for rambling on. Aspergers is not going away anytime soon, the best approach is to be positive, someone will come along and tell us what’s really happening with autism. If they are anything like Marie Currie, it will be for the good of mankind, instead of some fat cats pocket...

You come from a multiplex autism family (a family where at least two people are on the spectrum). Which means chances are very high that there's a genetic component to your family's autism.

Not knowing which genes are involved, it's impossible to say how likely it is that you'd have an autistic kid.

In terms of single gene conditions, your family's pattern would be consistent with an X-linked trait with variable penetrance (eg Fragile X Syndrome). Basically, with a condition like this, all boys with the gene would be affected, while girls with the gene might be affected or carriers. Your mother would be an unaffected carrier. In theory, you'd have a 50% chance of being a carrier, but in practice, it would be lower because we already know you're not affected. (For example, if 50% of girls with the gene are affected, you as an unaffected girl would have a 25% chance of having the gene. But without knowing what percentage of girls with the gene are affected we couldn't give an exact number.) If you happen to be a carrier, your sons would have a 50% chance of being affected, and your daughters would have a lower but still elevated chance. If you're not a carrier, then there's virtually no chance of an affected child.

It would also be possible for the condition to be autosomal recessive, with your mother just happening to pick two guys who both carried the same recessive gene. In that case, you'd have a 67% chance of being a carrier (a child of two carriers has a 25% chance of being affected, 50% chance of being a carrier and 25% chance of not having the gene at all, but we already know you're unaffected so we can only look at the carrier versus non-carrier part of it). If you're a carrier, your chance of having a child with the condition depends on whether you marry a carrier - if you do, it's 25%, if not, it's pretty much zero (barring a random mutation, which is extremely rare). If you're not a carrier, there's virtually no chance of having an affected child.

Dominant with incomplete penetrance could apply as well. (This is how Tourette Syndrome, for example, is inherited.) In this case, your mother would have the gene but be unaffected, and passed on the gene to your two siblings. Your likelihood of having the gene would be affected by the penetrance of the gene - it could range from almost 50% (low penetrance) to extremely low (high penetrance). If you were a carrier, your likelihood of having an affected child would also depend on the penetrance, being close to 50% for high penetrance and extremely low for low penetrance.

Then there's polygenetic inheritance, which is thought to explain most cases of autism. This would mean that you have to have the right combination of several genes (possibly up to hundreds of them) in order to be affected. In this case, we'd need to know exactly how many genes were involved and how they worked to know the risk. Since we don't know that, the answer would be that it's somewhat higher, but still fairly low - somewhere in the ballpark of 5%? (Note: This is a wild guess - this is usually around the probability of recurrance for polygenetic traits.)

And then there's the possibility of a chromosome abnormality, which is especially likely if your siblings on the spectrum have an odd physical appearance, congenital anomalies (eg heart defects, cleft lip/palate, etc) and/or cognitive delays. Since they're AS, it's probably safe to assume no cognitive delays (usually AS diagnosis requires normal IQ, though not every diagnostician follows that rule). If a chromosome abnormality was involved, the most likely would be a translocation. In this case, your mother would have a balanced translocation - for example, she might have the tips of 11q and 8p swapped. A balanced translocation means all the information is there, but it's in a different order. Her children would have a chance of either inheriting the normal 8 and 11 (or whichever chromosomes are involved) and being normal, inheriting the translocated 8 and 11 and being carriers, or inheriting a translocated chromosome and a normal chromosome and being affected (if it was 8p and 11q, you could have 8p duplication/11q deletion or you could have 8p deletion/11q duplication). There's a roughly 50% chance of a child of a balanced translocation carrier having an unbalanced translocation (a bit lower in practice because unbalanced translocation carriers are more likely to be miscarried early on). If you're unaffected, there's be a 50% chance of having a balanced translocation.

Then, of course, not all multiplex families have a genetic cause for autism. If your mother, for example, was continually affected by some illness with no overt effect, but which had the chance of causing brain damage to a fetus, you'd have multiple affected kids with no genetic cause. Or she could have had difficult labours due to some injury or illness she suffered at some point, which would also be a non-genetic cause. Or the genetic link could be a tendency to difficult labour, in which case your probability of having an autistic kid would depend on whether you've inherited the difficult labour gene(s), and the autism itself wouldn't be genetic at all.

All in all, it's complicated. If you want to know better what your likelihood of having an autistic kid is, you'd probably need to get your siblings tested for the identified autism genes, and if they test positive for anything, you can get yourself tested and get more detailed information. But that would be expensive, and it's possible you'd find nothing at all (many autism genes are unindentified).

Also, if it's polygenetic, or if it's a dominant or X-linked trait with incomplete penetrance, you might be on the broader autistic phenotype. If so, that indicates that you're more likely to have an autistic kid. If it's polygenetic, being BAP means you have several of the autism genes, while if it's single gene with incomplete penetrance, being BAP makes it almost certain you're a carrier. Of course, if you aren't BAP, it doesn't mean you don't carry one or more autism genes that haven't had any effect on you. Still, you can check out if you're BAP by taking this test.

PS: Can you tell that genetics is one of my intense interests? Despite no formal training, I've been told I know as much about genetics as many clinical geneticists.