Abstract
High levels of circulating anti-Mullerian hormone are unique to developing males, but the function of anti-Mullerian hormone in boys is unknown. In mice, anti-Mullerian hormone contributes to the male biases in the brain, but its receptors are present throughout non-sexually dimorphic portions of the brain. In humans, the speed of maturation is the most overt difference between girls and boys. We postulate that this is because anti-Mullerian hormone slows the maturation of the male human brain.
One hundred and fourty three 5-year or 6-year-old boys and 38 age-matched girls drew a person and donated a blood sample. The children's drawings were blind-scored to generate a maturity index. The level of anti-Mullerian hormone and the other Sertoli cell hormone, inhibin B, were measured by ELISA. The relationship between the children's age, hormones and maturity index were examined by linear regression analysis.
The girls drew more complex and realistic person than the boys (32%, p = 0.001), with their drawings also being larger (39%, p = 0.037) and more coloured-in (235%, p = 0.0005). The maturity index in boys correlated with age (+r = 0.43, p < 0.0005) and anti-Mullerian hormone level (-r = -0.29, p < 0.0005). The association between maturity index and anti-Mullerian hormone level persisted when corrected for age and for inhibin B (r = -0.24, p = 0.0005). The calculated effect of the median level of anti-Mullerian hormone (1 nM) was equal to 0.81 months of development. The size and colouring of the drawings did not correlate with the boys' age, anti-Mullerian hormone or inhibin B.
This exploratory study provides the first indicative evidence that circulating anti-Mullerian hormone may influence the development of the human brain.