The complex process of sexual differentiation is known to be influenced by biological and environmental determinants. The present review has the aim of summarizing the most relevant studies on the biological basis of sexual development, and in particular, it focuses on the impact of sex hormones and genetic background on the development of sexual differentiation and gender identity. The authors conducted a search of published studies on Medline (from January 1948 to December 2019). The evidence suggests that the sexual dimorphic brain could be the anatomical substrate of psychosexual development, on which gonadal hormones may have a shaping role during prenatal and pubertal periods. Additionally, according to several heritability studies, genetic components may have a role, but a promising candidate gene has not been identified. Even though growing evidence underlines the primary role of biological factors on psychosexual development, further studies are necessary to better explain their complex interactions.

In Italy, studies investigating gender identity and expression in gender non-conforming adults are lacking, as well as data regarding the non-binary population. The present study aimed at dimensionally exploring how transgender and non-binary Italian adults identify and express their gender. The Gender Diversity Questionnaire (GDQ) was administered to a sample of 112 adult subjects aged 18–60 years accessing a gender-specialized service in Rome. The majority of the participants were aged 18–24 years (53.6%), whereas fewer subjects were aged 25–35 years (32%) and 35 years and older (14.3%). Most participants (83.9%) identified themselves as trans binary, while the remaining (16.1%) identified as non-binary. Trans binary participants reported a stable gender identity, whereas non-binary participants reported a more fluid gender identity over time and across contexts. Younger subjects recognized the use of chosen names, pronouns, and clothes as important for their gender expression, whereas older subjects attributed more importance to physical appearance and emotions. Differences regarding gender-affirmative interventions emerged between non-binary and transbinary participants. Findings evidence that gender non-conforming adults accessing gender-specialized services have unique needs and features, thus it is essential to shed light on this population by providing greater visibility and recognition.

Considering the lack of research and literature in Italy about Gender Identity Disorder (GID) in children and the importance of an early diagnosis, the authors administrated the “Gender Identity Interview” ( Zucker et al., 1993 Zucker, K. J. , Bradley, S. J. and Sanikhani, M. 1997. Sex differences in referral rates of children with gender identity disorder: Some hypotheses. Journal of Abnormal Psychology, 25: 217–227. [Google Scholar] ) to 350 children of 3, 4, and 5 years of age in seven different kindergartens in Florence, Italy. The aim of the research was to obtain a descriptive analysis of the main characteristics of gender identity in preschool children in relation to sex and age and to estimate the prevalence of gender dysphoria in this group. This was the first research about gender identity in preschool children in Italy and could represent a basis for further studies in this field.

The sample size and data collection period of the original publication