Thousands of animal experiments have demonstrated that androgenic hormones, such as testosterone, during the prenatal and early postnatal periods, masculinise and defeminise various neural and behavioural characteristics that differ by sex. Can these findings from animal experiments be generalised to human behaviour? Can early androgen exposure shape subsequent gender-related disorders in humans? Chapter 1 (Introduction) provides an overview of the literature. Chapter 2 (Kung et al., 2016a) is the first study to demonstrate that testosterone concentrations in saliva samples collected during the early postnatal testosterone surge at 1 to 3 months of age can negatively predict subsequent expressive vocabulary size (how many words a child can say) during toddlerhood. Notably, males typically have a smaller expressive vocabulary than do females during toddlerhood and a small expressive vocabulary is predictive of subsequent language difficulties, such as dyslexia and stuttering, which are more common in boys. Chapters 3 (Kung et al., 2016b) and 4 (Kung et al., 2016c) evaluate a popular theory of autism, the extreme male brain theory, which argues that heighted androgen exposure during early development causes the male preponderance in autism. To test the hypothesised relationship, Chapters 3 and 4 use different measures and study populations, including testosterone concentrations in amniotic fluid samples obtained prenatally and saliva samples obtained during the early postnatal testosterone surge in typically developing children, as well as examining the adjustment in children exposed to unusually high levels of androgens prenatally due to congenital adrenal hyperplasia (CAH), a rare clinical condition occurring in approximately 1 in 18,000 births. Findings from these two chapters converge to show that any relationship between early androgen exposure and subsequent development of autistic traits is small, non-existent, or unreliable, providing a much-needed clarification of the role of early androgen exposure in the aetiology of autism. Using data from a general population study, Chapter 5 (Kung et al., 2018a) is the first study to show that male-typical play behaviour in early childhood, a trait that has been linked to increased early androgen exposure in previous research, can positively predict adolescent physical aggression, which is typically higher in males than in females. This positive association between play and aggression supports potential influences of early androgen exposure, as well as socio-cognitive influences involved in gender development. Chapter 6 (Kung et al., 2018b) is the first study to compare emotional and behavioural adjustment in children with CAH, their unaffected siblings, and children in the general population. Findings from this chapter suggest that although within the families with a child with CAH there are
generally no differences in emotional or behavioural problems between boys or girls with CAH and their unaffected same-sex siblings, both girls with CAH and their unaffected sisters are at risk of developing behavioural problems when compared with girls in the general population. Familial influences and social stigma may contribute to this gender-specific pattern of behavioural adjustment. Finally, Chapter 7 (Discussion) integrates the findings and previous research and provides directions for further research.

Chapter References

Chapter 2

Kung, K. T. F., Browne, W. V., Constantinescu, M., Noorderhaven, R. M., and Hines, M. (2016). Early Postnatal Testosterone Predicts Sex-Related Differences in Early Expressive Vocabulary. Psychoneuroendocrinology, 68, 111-116.

Chapter 3

Kung, K. T. F., Constantinescu, M., Browne W. V., Noorderhaven, R. M., and Hines, M. (2016). No Relationship Between Early Postnatal Testosterone and Autistic Traits in 18 to 30-Month-Old Children. Molecular Autism, 7:15.

Chapter 4

Kung, K. T. F., Spencer, D., Pasterski, V., Neufeld, S., Glover, V., O'Connor, T. G., Hindmarsh, P. C., Hughes, I. A., Acerini, C. L., and Hines, M. (2016). No Relationship Between Prenatal Androgen Exposure and Autistic Traits: Convergent Evidence from Studies of Children with Congenital Adrenal Hyperplasia and of Amniotic Testosterone Concentrations in Typically-Developing Children. Journal of Child Psychology and Psychiatry, 57, 1455-1462.

Chapter 5

Kung, K. T. F., Li, G., Golding, J., and Hines, M. (2018). Preschool Gender-Typed Play Behavior at Age 3.5 Years Predicts Physical Aggression at Age 13 Years. Archives of Sexual Behavior, 47, 905-914.

Chapter 6

Kung, K. T. F., Spencer, D., Pasterski, V., Hindmarsh, P. C., Neufeld, S. A. S., Hughes, I. A., Acerini, C. L., and Hines, M. (2018). Emotional and Behavioral Adjustment in 4- to 11-Year-Old Boys and Girls with Classic Congenital Adrenal Hyperplasia and Unaffected Siblings. Psychoneuroendocrinology. 97, 104-110.