The Relationship Between Foetal Testosterone Exposure, Head Circumference, and Repetitive Behaviours in Typically Developing Preschool and Older Children

Background: While suggestions of a relationship between foetal testosterone (fT) levels and autistic-like traits in the typically developing population (e.g. Auyeung et al., 2009) have catalysed a great deal of research and attention, surprisingly little work has been conducted on fT’s effect on postnatal growth patterns.  Abnormal growth trajectories have been noted in autism, namely a period of neural overgrowth (Redcay and Courchesne, 2006) as well as possibly faster corporeal growth (Dissanayake et al., 2006).  Animal studies suggest fT exposure has gender-specific effects on postnatal growth patterns (Von Engelhardt, 2006).  For instance, fT has been implicated in the development of behaviours such as persistent and repetitive actions (Schwabl, 1996) and faster perceptual learning and discrimination (Bertin et al., 2009), all features noted in autism (Singer, 2009; Jones et al., 2009). Indeed Schwabl (1996) suggests the increased growth associated with increased fT exposure in birds is the result of these persistent and fixated behaviours, as these translate to effective food begging actions.

Objectives: This study aimed to look at the effects of fT on one aspect of physical growth, head circumference (HC), in a typically developing population of children and if there were any interactions or relationships between HC and the presence of repetitive behaviours.  HC is thought to be a robust indicator of brain volume in children (Hazlett et al., 2005), and as such is an easily obtainable proxy of both individual differences in brain growth in typically developing children and of early atypical neural growth trajectories in autism (Redcay & Courchesne, 2005). Only two studies have analyzed the effects of fT on brain size in humans, both using indirect measures of fT. Ronalds et al., (2002) found weak effects of 2d:4d on birth HC to birth length ratios in males with larger than average placentas. Peper et al., (2009) found that 9 year old children with a twin brother, thus exposed to higher intrauterine levels of fT, had larger brain volumes than those children with a female co-twin, although this was not replicated in adults.

Methods: Two groups of typically developing children, one 3-5 years (25 male, 25 female) and one 9-13 years (25 female and 25 male) for whom amniotic fT levels were assayed at 14-22 weeks of gestation were followed up in a large longitudinal study. Head circumference, height, and a questionnaire measure of repetitive behaviours (RBQ-2; Leekam et al., 2007) were analysed.

Results: Multiple regression and correlation analyses were performed on the data, results indicate that fT  influences both absolute and relative head size.  Preliminary analysis suggests a role of fT on head size in females and a relationship between head circumference and repetitive behaviors. Gender differences and age-related changes were also analysed.

Conclusions: These results will be discussed, as well as a consideration of how these findings advance our current state of knowledge of hormonal and allometric differences in autism.