Prevalence of our lack of the social mindset

We have two direct sources that I have been able to use to form an estimate for the prevalence of our severity and presentation of our condition.

I have displayed it below in comparison to an estimate for the prevalence of those with Asperger syndrome also meeting criteria for schizoid personality disorder based on two studies. (See Schizoid personality disorder for the explanation behind the inclusion of this diagnosis.)

• Using an average (roughly adjusted for confounding factors) from our direct sources (two samples totalling around 300 people, one of which included ourselves), the prevalence of our condition would be around 0.013%, or 1 in 7,500 people.
• Using an average from the two comorbidity studies on those with Asperger syndrome also meeting criteria for schizoid personality disorder, the prevalence of this combination would be around 0.038%, or 1 in roughly 2,632.

According to figures from one of the comorbidity studies, combined with the sex ratio of Asperger syndrome, the sex ratio of those who are considered to meet both the criteria of Asperger syndrome and schizoid personality disorder alone would be around 14.4 males to 1 female.

However, our severity and presentation goes well beyond the criteria of Asperger syndrome and schizoid personality disorder, and a number of lines of evidence discussed below lead us to believe it is unlikely that a female exists with our severity and presentation of our condition.

Our samples

Two samples each contained roughly 150 age-matched male individuals who scored in roughly the top 15% on a set of verbal and non-verbal reasoning tests (i.e. roughly more than one standard deviation above average).

The first sample included ourselves but no one else with our condition. Thus, out of the first sample, those with our condition (ourselves) comprised 2, or roughly 1.3%.

The second sample did not contain anyone with our condition.

Despite the intelligence scores of the samples being roughly above the 85th percentile, as mentioned on Other features of our lack of the social mindset, at age 16, my friend achieved scores that placed him in about the 98th percentile (two standard deviations above average) on the Cattell Culture Fair Intelligence Test. Although I have not yet completed a standardised IQ test such as Cattell, Weschler, Stanford–Binet or Raven’s, as described on the same page, my abilities generally parallel my friend’s.

It is notable that out of the two samples, whose mental abilities were already roughly more than one standard deviation above average, the only two people with our condition had abilities roughly another standard deviation higher.

If one were therefore to conclude that such abilities were necessary for our severity and presentation of our condition (which has evidence on the site that is summarised below), the averaged figure of 1/150 males (roughly 0.67%) for both samples would need to be adjusted for the general population by dividing it by 50, to normalise for representation outside the 98th–100th percentiles.

This would place the prevalence of our condition at an estimated 0.013%, or 1 in 7,500 people.

For reference, including ourselves, the number of those in the first sample known to us to be diagnosed with an autism spectrum disorder was 4, or nearly 2.7%, while the number known to us with autistic traits suggestive of being sufficient for a diagnosis, which they may have had, was at least 8, or around 5.3%. All members of the samples had full language development.

If the first sample were controlled for sex using an 8:1 male-to-female ratio for Asperger syndrome (averaged from studies finding ratios of 12.07:1^[1] and 4.1:1^[2]), with the main confounding factor left being representation in the top 15% of verbal and non-verbal reasoning ability, the prevalence of Asperger syndrome in the first sample would be around 2.25–5 students out of 150 (or 1.5–3.0%), around 6–12 times higher than that of the general populace.

Asperger syndrome and schizoid personality disorder

According to a 2003 review, studies report varying prevalence rates of Asperger syndrome between 0.03% and 0.48%, giving an average of around 0.26%.^[3]

Although the DSM-5 references two studies that suggest a prevalence of either 3.1% or 4.9% for schizoid personality disorder,^[4] studies have generally reported a prevalence of less than 1%,^[5][6] including a 2006 study featuring results from eight different studies that, when averaged, give a prevalence of 0.65%.^[6]

Comorbidity studies

There are two studies to my knowledge that assessed samples of those with Asperger syndrome for meeting criteria of schizoid personality disorder (SPD).

A 2012 study found that 26% a sample of 54 adults with Asperger syndrome (mean age: 27, SD: 3.9; mean WAIS-III IQ: 102; 26 men, 28 women) also met criteria for SPD, a higher comorbidity than any other personality disorder in the sample.^[7]

A 2019 study found that 5.8% of a group of 50 males aged 11 to 25 with Asperger syndrome met full diagnostic criteria for SPD, compared to 0% of a control with other psychiatric disorders, with 54% showing significant SPD traits.^[8] After adjusting the 5.8% figure for sex according to the 8:1 male-to-female ratio for Asperger syndrome, this gives rise to a figure of 3.2625% for both sexes.

The much higher percentage in the 2012 study is likely the result of two main factors: the study had a higher mean sample age, and it took participants from a study of links between Asperger syndrome and schizophrenia/schizoaffective disorder. Additionally, its sample was sex-controlled, and as such, it would probably not be expected that its percentage was more than four times that of the 2019 study’s male-only sample, given the links between male sex and negative symptoms of schizophrenia/schizoid personality disorder.

Regardless, if one were to average the sex-adjusted results of the two samples (14.63125%) and multiply this by the 0.26 average figure for the prevalence percentage of Asperger syndrome, one would get a prevalence of meeting the criteria of both conditions of roughly 0.038%, or 1 in roughly 2,632.

However, if one were to rely on the 2019 study’s sex-adjusted figure, this would give a prevalence of meeting the criteria of both conditions of roughly 0.0085%, or 1 in roughly 11,789.

Sex ratio

Although, as of the launch of this site, we had only seen one other male with our condition to our severity, we have seen several males with some features in common with our condition.

On the other hand, we have never seen a female have any significant resemblance to our condition, including those diagnosed with an autism spectrum disorder.

According to the aforementioned studies, for those who are considered to meet both the criteria of Asperger syndrome and schizoid personality disorder alone, the sex ratio would be around 14.4 males to 1 female, leading to figures of roughly 0.0079–0.0632% of males (or 1 in roughly 1,582–12,608 males) and roughly 0.00055–0.0044% of females (or 1 in roughly 22,781–181,550 females), which would equate to only 44,065–351,170 females on the planet.

However, a number of lines of evidence featured on this site lead us to believe it is unlikely that a female exists with our severity and presentation of our condition.

These are recapitulated below.

Asperger-syndrome severity

• A 2019 study found that copy number of the CON1 subtype of the Olduvai domain was incrementally associated with impaired social reciprocity (0.18 points for each copy) and communication (0.13 points for each copy) scores on the Autism Diagnostic Interview-Revised (ADIS-R) in males with high-functioning autism (without intellectual disability), with no significant association in females.^[9]
• A 2010 study of a large sample found a male-to-female ratio of 12.07:1 for Asperger syndrome (almost double that found for autism spectrum disorder as a whole).^[1] A 1993 study found a male-to-female ratio of 4.1:1 for Asperger syndrome.^[2] Other studies have also found lower sex ratios for autism spectrum disorder (especially with learning difficulties), as low as 2:1, and higher sex ratios for Asperger syndrome or high-functioning autism, as high as 16:1.^[10]

This evidence highlights the male-only significant association between copy number of the CON1 subtype of the Olduvai domain and severity of the primary symptoms of autism spectrum disorder in those without intellectual disability as well as the often-reported male predominance in Asperger syndrome, which is higher than that of autism spectrum disorder as a whole.

Our lack of the social mindset goes well beyond the clinical definition of Asperger syndrome.

Negative-symptoms severity

• A 2015 study found that increased copy number of the CON1 subtype of the Olduvai domain was associated with increased severity of negative symptoms of schizophrenia (blunted affect, anhedonia, avolition, alogia and asociality^[4]) in males, with no significant association in females.^[12]
• Male sex has been repeatedly linked to the negative symptoms of schizophrenia.^{[13][14][15][16]}
• A 2014 study found that nearly two thirds of those with schizoid personality disorder (SPD) were male.^[17]
• The 2012 study of a sex-controlled sample with Asperger syndrome with average intelligence found that nearly twice as many men with the disorder (64.3%) met criteria for SPD than women.^[7]

This evidence highlights the male-only significant association between copy number of the CON1 subtype of the Olduvai domain and severity of the negative symptoms of schizophrenia (blunted affect, anhedonia, avolition, alogia and asociality) as well as the often-reported male predominance in negative symptoms of schizophrenia and schizoid personality disorder (which comprises many of the negative symptoms of schizophrenia).

As discussed on the Schizoid personality disorder section of Schizophrenia and autism, although we would most likely be considered to meet the diagnosis of schizoid personality disorder if we did not meet the criteria for autism spectrum disorder, it too does not fully encapsulate our lack of the social mindset and contains a few elements that go against it.

Brain growth

• A 2012 study showed that, in individuals with 1q21-deletion- or duplication-associated microcephaly or macrocephaly, Olduvai copy number showed the strongest association with brain size, especially with regards to the three conserved subtypes (CON1, CON2 and CON3). CON1 (the subtype significantly associated above with severity of high-functioning autism and negative symptoms of schizophrenia in males only) showed the strongest association, followed by CON3 and CON2. The finding was replicated in the form of an association with grey-matter volume in a healthy sample.^[18]
• Megalencephaly in autism is largely restricted to males. A 1996 study of 35 individuals with autism found significantly increased brain volume in the males but not the females,^[19] and a 1995 study of a sample of 148 children with autism found that megalencephaly in autism was found overwhelmingly in males; whilst the male-to-female ratio was 5:1 for the entire sample, this rose to 27:1 for those with megalencephaly.^[20]
• A 2015 study found that increased copy number of the CON2 subtype of the Olduvai domain was associated with higher IQ (as assessed on the Wechsler Intelligence Scale for Children) and higher mathematical ability (as assessed on the New Zealand Progressive Achievement Test for Mathematics) in males, with no significant association in females.^[21]
• A 2005 meta-analysis of 22 studies of sex differences in intelligence in university students calculated the means and variability of male and female IQs as measured by Raven’s Progressive Matrices. The resulting means, which were 5 points higher for males than females, combined with the general IQ distribution, meant that the male-to-female ratio would be 2.3:1 for those with an IQ of 130+, 3:1 for 145+ and 5.5:1 for 155+.^[22]
• Modern human intracranial volume is around 1,270 cm³ for males and 1,130 cm³ for females.^[23]

This evidence highlights the male-only significant association between copy number of the CON2 subtype of the Olduvai domain and IQ, the association between CON1 copy number and brain size (the subtype significantly associated with severity of high-functioning autism and negative symptoms of schizophrenia in males only), the overwhelming predominance of males in those with autism with megalencephaly and the often-reported predominance of males in the higher IQ ranges.

Although megalencephaly is characteristic of autism spectrum disorder, it is only found in around 20% of those with the disorder.^[24] Similarly, in these cases, it does not always result in above-average intelligence.^[25]

However, both of us had significant megalencephaly as children, and at age 16, my friend achieved scores of 137 on form A (99th percentile) and 144 on form B (97th percentile) on scale 3 of the Cattell Culture Fair Intelligence Test, with myself demonstrating abilities that parallel my friend’s.

References

1. ^ ^{a b} Whiteley, Paul; Todd, Lynda; Carr, Kevin; Shattock, Paul (2010). "Gender Ratios in Autism, Asperger Syndrome and Autism Spectrum Disorder". Autism Insights. 2: 17–24.
2. ^ ^{a b} Ehlers, Stephan; Gillberg, Christopher (1993). "The Epidemiology of Asperger Syndrome". Journal of Child Psychology and Psychiatry. 34 (8): 1327–1350. doi:10.1111/j.1469-7610.1993.tb02094.x. ISSN 1469-7610.
3. ^ Fombonne, Eric; Tidmarsh, Lee (2003-01). "Epidemiologic data on Asperger disorder". Child and Adolescent Psychiatric Clinics of North America. 12 (1): 15–21, v-vi. doi:10.1016/s1056-4993(02)00050-0. ISSN 1056-4993. PMID 12512396.
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16. ^ Guo, Meng En; Collinson, Simon Lowes; Subramaniam, Mythily; Chong, Siow Ann (2011-02-01). "Gender differences in schizotypal personality in a Chinese population". Personality and Individual Differences. 50 (3): 404–408. doi:10.1016/j.paid.2010.11.005. ISSN 0191-8869.
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22. ^ Irwing, Paul; Lynn, Richard (2005). "Sex differences in means and variability on the progressive matrices in university students: A meta-analysis". British Journal of Psychology. 96 (4): 505–524. doi:10.1348/000712605X53542. ISSN 2044-8295.
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