Left-Handedness in Male-to-Female Transsexuals

To the Editor.  —Although the origin for disturbances of sexual orientation and gender identity is not known, several lines of evidence suggest the importance of biologic factors. One often-suggested factor is hormonal fluctuations in utero that alter sexual differentiation of the brain and lead to inappropriate masculinization or feminization.¹ Another possibility is that some form of prenatal stress has taken place that has disturbed the normal development and gender differentiation of the brain. Handedness provides an accessible behavioral marker that may clarify the origin of disturbed gender identity.Over the past decade, data have accumulated that suggest that elevated prenatal testosterone levels may be associated with an increased incidence of left-handedness.² Higher rates of left-handedness are also related to prenatal and perinatal stressors, including low birth weight, prolonged labor, birth-related anoxias, Rh incompatibilities, multiple births, breech births, and prematurity.^3,4 These two sources of increased sinistrality allow us