We present a female infant with unambiguous genitalia with a ring chromosome composed of both X and Y sequences. Pregnancy, labor and delivery were normal. Birth weight was 3160 g (50th%ile), length at birth 50.8 cm(75th%ile) and head circumference 33 cm (10th%ile). Physical findings included mild frontal bossing, low posterior hairline, inner canthal folds, and moderate edema over both hands and feet. The toenails were hyperconvex. Echocardiogram revealed patent foramen ovale and ductus arteriosus, and left ventricle strands. Renal ultrasound was normal.

Chromosome analysis of amniotic fluid cells revealed a 45,X karyotype in all cells examined. A repeat karyotype of lymphocytes obtained after birth revealed a mosaic karyotype with 47% of metaphase cells showing a 45,X karyotype and 53% having a 46,X + ring chromosome composition. FluorescenceIn-Situ Hybridization (FISH) was applied to determine the genetic make-up of the ring chromosome. No signal was detected on the ring using an X chromosome alpha satellite probe indicating the absence of an X centromere in the ring, however, application of an X chromosome paint probe identified half of the ring to be X-derived. A Y chromosome cocktail probe yielded signals on the other half of the ring with identification of both the centromeric alpha satellite region (DYZ3) and the distal Yq classic satellite region (DYZ1). The karyotype of the cell line with the ring is 46,X,r(X;Y). PCR-based analysis of lymphocyte DNA revealed that the ring chromosome contained sequences from the Y chromosome including the pseudoautosomal boundary and the SRY, RPS4Y, ZFY, and KALP genes. X-chromosome analysis using a panel of highly polymorphic markers indicated the ring contained genetic material derived from Xp22.1 to Xp21.3. Thus, this patient likely carries two active copies of the dosage sensitive sex reversal (DSS) gene, perhaps explaining the female phenotype of this patient in the presence of the SRY gene.