Beyond a Binary Classification of Sex: An Examination of Brain Sex Differentiation, Psychopathology, and Genotype. Journal of the American Academy of Child and Adolescent Psychiatry Phillips, O. R., Onopa, A. K., Hsu, V., Ollila, H. M., Hillary, R. P., Hallmayer, J., Gotlib, I. H., Taylor, J., Mackey, L., Singh, M. K. 2018


OBJECTIVE: Sex differences in the brain are traditionally treated as binary. We present new evidence that a continuous measure of sex differentiation of the brain can explain sex differences in psychopathology. The degree of sex differentiated brain features (ie, features that are more common in one sex) may predispose individuals toward sex-biased psychopathology and may also be influenced by the genome. We hypothesized that individuals with a female-biased differentiation score would have greater female-biased psychopathology (internalizing symptoms, such as anxiety and depression), whereas individuals with a male-biased differentiation score would have greater male-biased psychopathology (externalizing symptoms, such as disruptive behaviors).METHOD: Using the Philadelphia Neurodevelopmental Cohort database acquired from database of Genotypes and Phenotypes, we calculated the sex differentiation measure, a continuous data-driven calculation of each individual's degree of sex differentiating features extracted from multimodal brain imaging data (Magnetic resonance imaging (MRI) /Diffusion MRI) from the imaged participants (n=866, 407F/459M).RESULTS: In males, higher differentiation scores were correlated with higher levels of externalizing symptoms (r=0.119, p=0.016). The differentiation measure reached genome-wide association study significance (p<5*10-8) in males with single nucleotide polymorphisms Chromsome5:rs111161632:RASGEF1C and Chromosome19:rs75918199:GEMIN7, and in females with Chromosome2:rs78372132:PARD3B and Chromosome15:rs73442006:HCN4.CONCLUSION: The sex differentiation measure provides an initial topography of quantifying male and female brain features. This demonstration that the sex of the human brain can be conceptualized on a continuum has implications for both the presentation of psychopathology and the relation of the brain with genetic variants that may be associated with brain differentiation.

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