“I’m Here to Get Taller and Because I Want to Be a Boy”: A Case of Down-Turner Mosaicism in a Prepubescent Gender-Nonconforming Child

Youth with differences/disorders of sex development (DSD) exhibit higher rates of gender dysphoria (GD) compared to the general population, though rates vary widely as a function of syndrome, syndrome severity, and initial gender assignment. Classical Turner syndrome is classified as a sex chromosome DSD; it is a genetic condition characterized by X-chromosome monosomy, short stature, complete gonadal dysgenesis, and female typical external genitalia. Approximately 50% of all females with Turner syndrome have some type of mosaicism, and approximately 6% have mosaic 45,X/46,XY with as high as 12% having some Y chromosome material present. Despite falling under the DSD classification, neither classical Turner syndrome nor Turner syndrome with Y chromosome mosaicism has been reported in the literature to be associated with GD. Here we describe a prepubescent gender-nonconforming birth-assigned female whose parents initially presented for consultation regarding gender nonconformity. Subsequent evaluation for short stature revealed 45,X/47,XY + 21 Down-Turner mosaic karyotype. To our knowledge, our patient is the first with Down-Turner mosaicism with phenotypic female genitalia and among the first reported cases of GD with comorbid Turner syndrome with Y chromosome mosaicism.