What causes an individual to have a particular gender identity? What precisely is it about biology, psychology, environment or some complex combination of all of these factors that makes a person feel male or female, neither or both? Exactly why do an estimated one in 100 individuals have what are medically considered "disorders of gender identity"—that is, psychological gender identities that differ from their physical sex?
Study in endocrine practice
To date, no scientifically definitive answers have been provided for these questions. Nevertheless, the most comprehensive scientific review of published literature on the causes of gender identity is "Evidence Supporting the Biologic Nature of Gender Identity," published in the journal Endocrine Practice in 2015 www.medscape.com/viewarticle/840538_1 ). In that review article, researchers from Boston University School of Medicine and Boston Medical Center ( Joshua D. Safer, MD; Aruna Saraswat, MD; Jamie D. Weinand, BA, BS ) concluded that available evidence suggests that there is a biological basis for gender identity.
The review article examined a wide range of conditions associated with gender, including some involving physical developmental abnormalities ( or disorders of sex development, such as those in intersex individuals ) and others with no obvious physical presentation. Among the biological factors linked to gender identity in these various cases were visible congenital disorders of sexual development ( such as penile ablation/agenesis [incomplete development] in intersex people ), unusual patterns of brain development ( such as female-type neuron numbers in a brain structure called the bed nucleus of the stria terminalis in genetic males ), and genetic changes resulting in hormonal variations ( such as mutations in the CYP17 gene ). The strongest evidence that biological factors are responsible for gender identity came from studies of intersex individuals, though significant evidence of such an association was also found in studies of other individuals identifying as transgender.
Although not 100-percent definitive, the results of the Boston study provided the "most convincing evidence to date" for biological causes of gender identity, according to Safer. However, the investigators admitted that the strength of their conclusions was limited by the relatively small sizes of the patient populations examined in the review. The researchers called for more and larger studies into specific biological factors that might contribute to gender identity.
The results of the Boston study also provided evidentiary support for biological-based treatments for patients struggling with gender identity—primarily hormonal therapy and surgical interventions to make the individual's body conform to his or her self-identified gender—rather than simply psychiatric treatment. Such science-based support—should it become backed by additional research—may prompt more physicians to overcome their reluctance to prescribe hormonal and surgical gender treatment for their patients who identify as trans.
New correspondence with Safer
In correspondence with this reporter in January 2017, Safer, who is the director of transgender medicine and surgery at Boston Medical Center, reiterated that the most powerful evidence for a biology-based gender identity comes from the "unfortunate experience[s] of intersex individuals in the recent past, and the treatment failure owing to the then unrecognized fact that gender identity is an innate biological phenomenon…"
Note: This is the first of a series of articles summarizing selected recent scientific studies related to LGBT issues.
