The male to female ratio in autism spectrum disorder is around 4:1. However it seems ASD is not a simple X-linked disorder.
Then how is it possible males are more susceptible than females, if the causal genes are located in autosomes?
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$\begingroup$ Could you maybe add some background, e.g. references on the incidence of autism spectrum disorders? $\endgroup$– fileunderwaterJun 13, 2013 at 11:12
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$\begingroup$ Sure, I will do this later when I come to school $\endgroup$– tkyJun 14, 2013 at 0:47
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4 Answers
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As the father of two sons with diagnoses of ASD, I think that it is best to think in terms of an extended spectrum which encompasses 'normal' people. We are all somewhere on this spectrum, but there is a threshold zone around where we cross from "normal" to "diagnosable as ASD". Now, if the distribution of spectral position for males is displaced towards the ASD end of the spectrum relative to females (because of some aspect underlying "normal' maleness, such as testosterone levels) then any genetic variation which pushes someone towards the ASD end of the spectrum by some fixed amount will tend to push more males over the threshold than females.
answered Jun 12, 2013 at 23:19
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$\begingroup$ That is an interesting idea. Do you know if there's a database of scores on an ASD questionnaire, for the general population so that we could verify it? Simon Baron-Cohen's tests come to mind, but I'm not sure if they've looked at the distribution of scores. $\endgroup$– blepJun 12, 2013 at 23:37
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$\begingroup$ Dear Alan, thanks for sharing the point. I hope the genetics study in the future can explain the mystery. $\endgroup$– tkyJun 13, 2013 at 15:05
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$\begingroup$ Nice thinking @alan-boyd, I wonder would it be nice to see a study correlating "manliness traits" with ASD test scores? $\endgroup$– rg255Jun 24, 2013 at 19:06
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$\begingroup$ This spectrum that leads to autism on the far right tail is probably the empathising-systemizing trait, which shows half a standard deviation mean difference between man and women. This difference in mean pretty exactly results in the 4:1 ratio in a normal distribution, if you look at the right tail that corresponds to the autism incidence rate. $\endgroup$ Aug 7, 2017 at 13:26
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Males are more likely to develop ASD, but affected females tend to be more severely impaired. Why this occurs is an area of active research.
However, to address your question, there is a study suggesting that mutations on the X-chromosome account for about 1% of ASD and intellectual disability cases. This clearly doesn't explain everything, but it's a start. It might suggest that there are other X-linked loci involved. IIRC, ASD is one of those disorders that can be caused by many different combinations of (relatively rare) mutations, so it's hard to identify the genetic causes by GWAS.
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$\begingroup$ hi, thanks a lot for the explanation. Another question came to my mind is that the one copy of X chromosome will be silenced (please correct me if I am wrong),so does the X chromosome which carry mutation always be deactivated? $\endgroup$– tkyJun 13, 2013 at 15:07
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I'm not expert on the topic, but whenever males more predominately have a condition than females, it might point to a sex-linked (recessive) trait. Males have one X chromosome, while females have two. This means that a male only needs one copy of a gene to have a condition (inherited from their mother), while females need two X chromosomes to be inherited to have the condition (mother and father).
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Being a Special Education Trainer at ACCEL Centre, I have done some research regarding this topic, but haven’t found a shred of full-proof evidence to support this theory.
Well, first of all, autism is a sensory integration disorder showing visible signs of speech delays and communication difficulty with others.
The main reason that causes autism spectrum is still not known and various researches are still in progress, together with erratic proof that men/women ratio ranges between 2:1 and 16:1.
One probable factor is a diagnostic bias, suggesting that females obtain autism diagnoses later in life as compared to males, indicating that it is harder to spot.
Signs of autism spectrum also look different in females. They have fewer restricted interests and repetitive behaviors and may have socially acceptable interests.
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