Subtle physical traits may hint at the biological roots of gender dysphoria

Researchers in Turkey have identified a potential biological link between early fetal development and the later emergence of gender dysphoria. The study indicates that adults diagnosed with gender dysphoria possess a higher frequency of subtle physical irregularities, known as minor physical anomalies, compared to cisgender individuals.

These physical traits develop during the initial stages of pregnancy and may serve as external markers for variations in brain development that occur during the same prenatal window. The research findings appear in the Journal of Sex & Marital Therapy.

The origins of gender dysphoria remain a subject of persistent scientific inquiry. Current theoretical models often divide potential causes into biological influences and psychosocial factors. A growing subset of neuroscience research examines whether the condition arises from variations in how the brain develops before birth. This perspective suggests that the biological pathways shaping the brain might also leave physical traces elsewhere on the body. This concept relies on the biological reality of fetal development.

During the early weeks of gestation, the human embryo consists of distinct tissue layers. One of these layers, the ectoderm, eventually differentiates to form both the skin and the central nervous system. Because these systems share a common embryological origin, disruptions or variations affecting one system often impact the other. Scientists have previously utilized this connection to study conditions such as schizophrenia and autism spectrum disorder. The presence of minute physical irregularities is often interpreted as a record of developmental stability in the womb.

These irregularities are classified as minor physical anomalies. They are slight deviations in morphology that do not cause medical problems or cosmetic concerns. Examples include low-set ears, specific hair whorl patterns, or a high arch in the palate. These features form primarily during the first and second trimesters of pregnancy. This timeframe overlaps with critical periods of fetal brain architecture formation. By quantifying these traits, researchers attempt to estimate the degree of neurodevelopmental deviation that occurred prior to birth.

Psychiatrist Yasin Kavla and his colleagues at Istanbul University-Cerrahpasa sought to apply this framework to the study of gender identity. They reasoned that if gender dysphoria has a neurodevelopmental basis, individuals with the diagnosis might exhibit these physical markers at higher rates than the general population. The team designed a case-control study to test this hypothesis. They aimed to determine if there is a measurable difference in the prevalence of these anomalies between transgender and cisgender adults.

The investigators recruited 108 adults diagnosed with gender dysphoria. These participants were patients at a university clinic who had not yet undergone hormonal or surgical gender-affirming treatments. The exclusion of individuals on hormone therapy was necessary to ensure that any observed physical traits were congenital rather than acquired. The group included 60 individuals assigned female at birth and 48 assigned male at birth. Most participants in this group reported experiencing gender dysphoria since early childhood.

For comparison, the researchers recruited a control group of 117 cisgender individuals. This group consisted of people who sought administrative health documents from the hospital. The control group included 60 females and 57 males who reported attraction to the opposite sex. The researchers implemented strict exclusion criteria for the control group. They removed any potential candidates who had a personal or family history of neurodevelopmental disorders, such as autism or attention deficit hyperactivity disorder.

Two psychiatrists examined each participant using the Waldrop Minor Physical Anomaly Scale. This assessment tool is a standardized method for evaluating 18 specific physical features across six body regions. The regions include the head, eyes, ears, mouth, hands, and feet. To ensure objectivity, the examiners used precise tools like calipers and tape measures for items requiring specific dimensions. They looked for specific signs such as a curved fifth finger, a gap between the first and second toes, or asymmetrical ears.

The analysis revealed distinct differences between the groups regarding the total number of anomalies. Individuals diagnosed with gender dysphoria had higher total scores for physical anomalies compared to the cisgender control group. This trend held true for both those assigned female at birth and those assigned male at birth. The data suggests a generalized increase in these developmental markers among the transgender participants. The researchers then broke down the data by specific body regions to identify patterns.

The disparity was most evident in the craniofacial region. This area includes the head, eyes, ears, and mouth. Both groups of transgender participants showed elevated scores in this region relative to the cisgender participants. Specific anomalies appeared more frequently in the gender dysphoria group. These included a furrowed tongue and skin folds covering the inner corner of the eye, known as epicanthus. The study notes that the face and brain exert reciprocal influences on each other during early embryogenesis.

The researchers also examined peripheral anomalies located on the hands and feet. Participants assigned female at birth showed higher scores in this category than both cisgender males and females. The results for participants assigned male at birth were more nuanced. Their peripheral scores were not statistically distinct from cisgender males. However, their scores were higher than those of the cisgender female control group. This suggests that the distribution of these traits may vary based on biological sex as well as gender identity.

Another measurement taken was head circumference. The study found that individuals assigned male at birth had larger head circumferences than those assigned female at birth, regardless of gender identity. There was no statistical difference in head size between cisgender males and transgender women. Similarly, there was no statistical difference between cisgender females and transgender men. This specific metric appeared to align with biological sex rather than gender identity or developmental instability.

The authors interpret these findings as support for a neurodevelopmental etiology of gender dysphoria. They propose that genetic and environmental factors in the womb likely drive the observed patterns. The presence of craniofacial anomalies specifically points to developmental variations occurring in the first two trimesters. This timing aligns with the period when the brain undergoes sexual differentiation. The findings challenge the notion that gender dysphoria is purely a psychosocial phenomenon.

However, the authors note several limitations that contextualize their results. The control group excluded anyone with a history of neurodevelopmental disorders. This exclusion might have artificially lowered the average anomaly score for the cisgender group. A control group including such histories might have produced different comparisons. Comparing the gender dysphoria group to a clinical psychiatric control group would clarify if these high scores are unique to gender dysphoria.

Additionally, the examiners could not be fully blinded to the participants’ gender presentation. This visibility might have introduced unconscious bias during the physical measurements. The study population also came from a single tertiary care center in Turkey. This sample may not represent the global diversity of gender-diverse individuals. Cultural and genetic background can influence the baseline prevalence of certain minor physical anomalies.

Sexual orientation represents another variable to consider. The majority of the transgender participants in the study were attracted to their same biological sex. The cisgender control group consisted entirely of heterosexual individuals. Future investigations would benefit from including cisgender control groups with same-sex attractions. This would help researchers isolate gender identity from sexual orientation as the primary variable.

The study concludes that minor physical anomalies are more prevalent in this specific cohort of individuals with gender dysphoria. This suggests that the biological roots of the condition may lie in early prenatal development. The authors emphasize that these anomalies are likely markers of underlying genetic or epigenetic processes. They call for future research to integrate genetic analysis to map the specific pathways involved.

The study, “Minor Physical Anomalies as a Gateway to Understanding the Neurodevelopmental Roots of Gender Dysphoria,” was authored by Yasin Kavla, Tuncay Sandıkçı, and Şenol Turan.