Swyer syndrome results from a failure of one of the earliest stages of differentiation of a genetic male: translation of the SRY gene to initiate testicular development. This syndrome represents one phenotypic result of a failure of the gonads to develop properly, and hence is part of a class of conditions termed gonadal dysgenesis. There are many forms of gonadal dysgenesis. As more and more specific genetic and molecular causes of gonadal dysgenesis become understood and defined, the eponymic terms such as Swyer syndrome are losing precision as diagnostic terms, though they still refer to a specific phenotype for purposes of medical recognition and management.

Swyer syndrome is an example of a condition in which an externally unambiguous female body carries dysgenetic, atypical, or abnormal gonads. Other examples include complete androgen insensitivity syndrome, partial X chromosome deletions, lipoid congenital adrenal hyperplasia, and Turner syndrome.

Although an XY karyotype can also indicate a girl with complete androgen insensitivity syndrome, the absence of breasts, and the presence of a uterus and pubic hair exclude the possibility. At this point it is usually possible for a physician to make a diagnosis of Swyer syndrome.

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