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Why are autistic people mainly male?

Posted Sep 17 2010 3:40am

Excluding the ever humorous ideas of the Geier’s and more serious ideas of Simon Baron-Cohen regarding testosterone, the reasons as to why there are (or seem to be) many more autistic males than females have not been adequately explained. However that might be about to change.

A new study gives the first starting point as to why this situation might come about.

As we all know , males have an X and a Y chromosome whereas females have two X’s. This new study postulates that this fact plays an important role.

If a boy’s X-chromosome is missing the PTCHD1 gene or other nearby DNA sequences, they will be at high risk of developing ASD or intellectual disability. Girls are different in that, even if they are missing one PTCHD1 gene, by nature they always carry a second X-chromosome, shielding them from ASD

The PTCHD1 gene is responsible for determining the development of human embryo’s and is already associated with autism. Because males only have 1 X chromosome, if this is defective then they – obviously – don’t carry that secondary level of shielding that females – with 2 X chromosomes – do.

However, this is very much preliminary. It should be noted that:

The researchers found that about one percent of boys with ASD had mutations in the patched domain containing 1 (PTCHD1) gene on the X-chromosome.

1% is not a very high number but as LBRB interviewee Stephen Scherer says:

The male gender bias in autism has intrigued us for years and now we have an indicator that starts to explain why this may be…

In other words, no one is saying this is a done deal – merely that its a strong possibility with some decent science behind it.

  1. Suvi-Tuuli Allan:
    Not all male humans have XY chromosomes, not all female humans have XX chromosomes. Know this!
  2. Kev:
    Agreed, but lets say 'in the main' :)
  3. Proofreader:
    Autisitc - typo "geier's" and "embryo's" don't own anything in these sentences. They are merely plural and should not have apostrophes.
  4. daedalus2u:
    This idea to explain the gender bias of ASDs is not correct. If there was a deletion on the X chromosome sufficient to cause the male excess, that would have absolutely jumped out of the whole genome scans that have been done. A second X chromosome does not "protect" females from the loss of a gene on one X chromosome. Females are mosaic, of their two X chromosomes, one is inactivated in somatic tissues. This is the issue with Rett Syndrome. RS is caused by a loss of the MeCP2 gene (on the X chromosome) and the MeCP2 protein which binds to methylated DNA and regulates its output. Males with MeCP2 deletion die in utero. The presence of some cells with MeCP2 somehow “rescues” females from death, but not from RS. That “rescue” is not due to expression of MeCP2 in cells where the MeCP2 containing X chromosome has been silenced. My explanation of the gender bias in ASDs is that it results from estrogen increasing NO levels and testosterone decreasing NO levels. This explanation is also consistent with the sub-clinical ASD-type characteristics that are more common in males than in females. SBC's “extreme male brain” is not the correct way of looking at it. ASDs have an “extreme low NO brain” and males tend to have a lower NO brain, so there are some similarities. It is the NO that comes first and is the main driver, the steroid hormones modulate the NO levels and there is feedback and hysteresis so it is very complicated (and not modifiable externally via things like lupron).
  5. Kev: people are busting my balls here ;)

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