XY gonadal dysgenesis

XY complete gonadal dysgenesis, also known as Swyer syndrome, is a condition resulting in a female phenotype in an individual with a 46,XY karyotype. Though they typically have normal vulvas, those affected typically have underdeveloped gonads, fibrous tissue termed "streak gonads", and without hormone replacement therapy, typically will not experience puberty. The cause is often, but not always, inactivation of the SRY gene, which is responsible for sexual differentiation. Pregnancy is sometimes possible in Swyer syndrome with assisted reproductive technology, and, in at least one case, without it.

The syndrome was named after Gerald Swyer, an endocrinologist based at London's University College Hospital, who first reported two cases in 1955.