Karyotypes, confined blood chimerism, and confusion: a case of genetic sex mislabelling and its potential consequences.

: Disorders of sex development (DSD) encompass a range of conditions, and the management of infants with DSD can be extremely complex. However, the misdiagnosis of a normal infant as a case of DSD may lead to unfortunate long-term consequences for the individual and the family. We report a case of confined blood chimerism masking as 46 XY gonadal dysgenesis in a female from a twin pair with discordant genders, which led to incorrect sex determination at birth. The potentially serious consequences of a wrong DSD diagnosis are discussed, including the removal of normal ovaries. This case emphasises the importance of confirming a blood karyotype where there is discordance with the clinical phenotype and, where possible, identifying whether functional gonadal tissue is present.