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46,XY monozygotic twins with discordant sex phenotype

S G Somkuti¹, S S Wachtel, J S Schinfeld

¹Department of Obstetrics and Gynecology, Abington Memorial Hospital, Abington, Pennsylvania, USA.

Fertility and Sterility

|December 20, 2000

Abstract

Objective:

To analyze male and female sex differentiation in monozygotic twins.

Design:

Retrospective study.

Setting:

Multiple academic centers.

Patient(S):

A pair of monozygotic twins.

Intervention(S):

Skin and blood samples were obtained for DNA analysis and karyotyping.

Main Outcome Measure(S):

Mutation within the SRY gene was analyzed by the polymerase chain reaction-single-stranded conformation polymorphism test. Monozygosity was ascertained by short tandem repeat analysis. Karyotypes were studied in blood and skin fibroblasts.

Result(S):

SRY was present in both twins, but no mutations were detected in the SRY conserved motif. Monozygosity was confirmed by the use of short tandem repeat analysis in four loci: c-fms, thyroid peroxidase, von Willebrand factor, and tyrosine hydroxylase. The karyotype was 46,XY uniformly in both twins.

Conclusion(S):

Monozygotic twins can develop discordant male and female phenotypes despite the presence of a common karyotype and despite the presence of intact testis-determining genes. In the present case, this could be due to mutation or to mosaicism involving occult 45,X cell lines in the dysgenetic gonads.

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