Differences By Gender in Rate of Autism Recurrence

Background:  Males with Autism Spectrum Disorder/Condition (ASD/ASC) outnumber equivalent females. Reasons for the gender disparity remain speculative. The historical conceptualisation of autism has shaped current diagnostic criteria and assessment tools, which may be insensitive in detecting female characteristics. Socialised gender roles and mechanisms adopted by females with ASC that obscure symptoms and underpin the ‘camouflage hypothesis’, may influence the sex skew. Such factors may lead to under diagnosis, misdiagnosis, or delayed diagnosis of ASC in females, precluding early intervention benefits and enhancing risk of adverse outcomes.

Objectives: This prospective investigation of school-aged children sought to explore the camouflage hypothesis by determining whether previously unidentified (PU) children with at least one older or younger sibling diagnosed with ASC show differential rates of diagnosis by gender. If more PU female siblings than PU male siblings of child probands with ASC screen positive for ASC traits, this would add support to the camouflage hypothesis.

Methods:  Clinicians with expertise in ASC in the state of Victoria, Australia, were asked to identify potential participants from their case files and forward research invitations to them. Advertising through ASC agencies also facilitated recruitment. Forty siblings (females=20) aged 6 to 17 years of child probands with a clinical diagnosis of ASC, and their parents, participated in the study. Child participants were assessed on cognitive ability (WASI-II), language (CELF-IV: Screener), behavioural presentation: Immediate (ADOS-2); Recent (AQ), and Lifelong (developmental history), adaptive functioning (VABS-II: Parent or Caregiver Rating Form), and female ASC attributes (GQ-ASC). Questionnaires were parent reported. Positive screens for ASC were determined by above cut-off scores on measures and clinical judgement, aligned with DSM-5 criteria for ASD.

Results: Based on previous literature it was expected that 18.7% of siblings, 26.2% of male siblings and 9.1% of female siblings of child probands with ASC would screen positive for the condition. Compared to expected estimates, the recurrence rate almost doubled for siblings of child probands with ASC in this study, with no difference in recurrence rate found for PU male siblings (30%), z =.376, p=.353, yet a highly significant difference in recurrence rate identified for PU female siblings (40%), z=4.26, p=<.001. The recurrence rate for PU males did not differ significantly from that of PU females (z=0.66, p=0.51).

Conclusions:  In families with ASC probands, the sibling recurrence rate of ASC in school aged children is higher than previously reported in infant siblings. More PU female siblings screened positive for ASC than PU male siblings, unexpectedly resulting in a narrower and reversed sex ratio. The recurrence rate for PU males corresponds with existing research, whereas, the recurrence rate for PU females reflects a four-fold increase from the earlier estimate, endorsing the camouflage theory. Implications of these findings regarding developmental manifestation of ASC, sibling assessments, and diagnostic considerations will be discussed.