Endocrine disruptors, the increase of autism spectrum disorder and its comorbidity with gender identity disorder – a hypothetical association

Dear Editor,

Recently, a paper was published in this journal suggesting that prenatal exposure to phthalate may be associated with a less typical male-typical play behaviour in boys (Swan et al., 2010). Phthalates are used in a large variety of household products and abound in our environment. They are endocrine disruptors, i.e. they interfere with the reproductive endocrine system and possibly with prenatal personality development and are positively associated with symptoms of Attention deficit hyperactivity disorder (ADHD) in children (Kim et al., 2009). Air-born phthalates indoors at the time of conception were related to an increased risk for autism spectrum disorder (ASD) in the offspring (Larsson et al., 2009). The comorbidity between these two disorders is striking and in childhood sometimes difficult to distinguish. People with ASD seldom become parents; nevertheless, genetic factors are considered crucial for the aetiology of ASD. An increase of de novo mutations has been reported, associated with environmental mutagenic factors. Altogether there has been increasing interest in vulnerability to environmental factors.

Individuals with ASD have difficulty with imitation, social imagination, non-verbal communication, social reciprocity and mind reading. One hypothesis that has been advanced to account for the cognitive style in ASD, is referred to as ‘the extreme male brain’. Based on the fact that normal males tend to rely more on systemising than empathizing on psychometric tasks, whereas the opposite is shown in females, autism can be considered as an extreme of the normal male profile. This model views ASD as resulting from increased testosterone exposure in utero. However, males with ASD are not super-masculine physically, rather they often look young, have sparse body hair and a high-pitched voice. Many are androgynous, not only in appearance, but also in their self-concept and ambiguous in sexual preferences (Hellemans et al., 2007). Females with ASD are likewise androgynous and have elevated testosterone levels (Geier & Geier, 2007). In persons with gender identity disorder (GID) the prevalence of ASD is 10-fold compared to the normal population (de Vries et al., 2010).

The spectrum of causes for the recent dramatic increase in reported rates of ASD are still hotly debated and various explanations have been proposed, ranging from elderly fathers to early vitamin D deficiency. We put forward the hypothesis that environmental chemicals of our own making may contribute to the increase and, consequently, that we already are forming a new human, more logical and non-manipulative, more concrete, more androgynous and sensitive, less sexual and social, for the good and for the bad.