Generalised joint hypermobility (GJH) is reportedly overrepresented among clinical cases of attention deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD) and developmental coordination disorder (DCD). It is unknown if these associations are dimensional and, therefore, also relevant among non-clinical populations.

To investigate if GJH correlates with sub-syndromal neurodevelopmental symptoms in a normal population.

Hakim-Grahame's 5-part questionnaire (5PQ) on GJH, neuropsychiatric screening scales measuring ADHD and ASD traits, and a DCD-related question concerning clumsiness were distributed to a non-clinical, adult, Swedish population (n=1039).

In total, 887 individuals met our entry criteria. We found no associations between GJH and sub-syndromal symptoms of ADHD, ASD or DCD.

Although GJH is overrepresented in clinical cases with neurodevelopmental disorders, such an association seems absent in a normal population. Thus, if GJH serves as a biomarker cutting across diagnostic boundaries, this association is presumably limited to clinical populations.

The ‘extreme male brain’ theory suggests that autism spectrum disorder (ASD) is an extreme variant of male intelligence. However, somewhat paradoxically, many individuals with ASD display androgynous physical features regardless of gender.

To assess physical measures, supposedly related to androgen influence, in adults with and without ASD.

Serum hormone levels, anthropometry, the ratio of 2nd to 4th digit length (2D:4D) and psychiatric symptomatology were measured in 50 adults with high-functioning ASD and age- and gender-matched neurotypical controls. Photographs of face and body, as well as voice recordings, were obtained and assessed with respect to gender coherence, blindly and independently, by eight assessors.

Women with ASD had higher total and bioactive testosterone levels, less feminine facial features and a larger head circumference than female controls. Men in the ASD group were assessed as having less masculine body characteristics and voice quality, and displayed higher (i.e. less masculine) 2D:4D ratios, but similar testosterone levels to controls. Androgynous facial features correlated strongly and positively with autistic traits measured with the Autism-Spectrum Quotient in the total sample. In males and females with ASD dehydroepiandrosterone sulfate did not decrease with age, in contrast to the control group.

Women with ASD had elevated testosterone levels and several masculinised characteristics compared with controls, whereas men with ASD displayed several feminised characteristics. Our findings suggest that ASD, rather than being characterised by masculinisation in both genders, may constitute a gender defiant disorder.