Gender Differences in Autism Spectrum Disorders in a Population-Based Twin Sample: testing three hypotheses for male preponderance.

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The proposed research aims to investigate gender differences across the full range of the autism spectrum, in a population-based sample of twins. Autism Spectrum Disorder (ASD) is a neurodevelopmental condition characterised by difficulties in social behaviour and communication, with restricted/repetitive behaviours and interests. One of the most striking features of ASD is the high male to female ratio, which varies across the spectrum, but is usually estimated at 4-5:1. The higher rate of ASD in males has been seen as a clue to the etiology of ASD; e.g. Baron-Cohen's 'extreme male brain' theory (Baron-Cohen, 2002) or the Female Protective Effect (FPE; e.g. Robinson et al., 2013). However, it is also possible that ASD is less well recognised in females, either due to male-stereotypes or genuine compensation. It is important to know whether current diagnostic practices miss females who would benefit from identification and intervention. The proposed study aims to address directly the question of whether females with high ASD traits are being missed by diagnostic practices or are instead coping/compensating and do not need a diagnosis. To do this the proposed research will compare four participant groups; females and males who meet diagnostic criteria for ASD, and females and males who score highly for ASD traits, but who do not meet diagnostic criteria. A battery of gold-standard diagnostic tools, cognitive tasks, measures of coping, quality of life, co-morbidities and mental and physical health will be completed by the four groups. This design will allow not only comparison of symptom presentation and cognitive profiles across genders, but also examination of whether high trait females without a diagnosis are compensating or instead 'suffering in silence'. It is vital to understand whether, and why, we fail to diagnose ASD in females, in order to clarify whether the current gender disparity is purely biological or also a reflection, in part, of problems with a male-focused conceptualisation, recognition, assessment or diagnosis of ASD.The proposed study is part of a longitudinal ASD twin study, nested within the larger Twins Early Development Study (TEDS). This design allows for the inclusion of non ASD co-twins and thus a more family wide exploration of gender, as well as specific examination of the FPE hypothesis, which suggests that a greater etiological 'load' is needed to result in ASD in females than males. Along with the FPE the proposed study tests two further, novel hypotheses: the 'Female Masking Effect' whereby females are less likely to receive a diagnosis of ASD because they are missed by male-focused diagnostic processes, and the 'Female Compensatory Effect' whereby females are less likely to receive a diagnosis of ASD because (in the absence of IQ/co-morbid problems) they cope better with high ASD traits via compensation and therefore do not need a diagnosis. The population-based design of the proposed study and the inclusion of the full ASD spectrum, address previous limitations with research in this area, such as possible sampling bias (due to use of clinic or volunteer register samples) and circularity (due to inclusion of only those meeting current diagnostic criteria).The proposed study has the potential to change the way we think about ASD; currently the accepted ratio of 4-5:1 informs research design and sample selection, and females are often excluded from research. The proposed study will tell the research/clinical/stakeholder communities whether and why this ratio may reflect bias in recognition/assessment/diagnosis, with far reaching implications for future research. In addition, the study has potential benefits for females with high traits/ASD by listening to and learning from their experiences. The proposed study has the potential to improve recognition of ASD in females, as a first step to targeting services and rebalancing the scientific and public perception of ASD.