Parental origin and mechanism of formation of a 46,X,der(X)(pter-->q21.1::p11.4-->pter)/45,X karyotype in a woman with mild Turner syndrome

Objective: To describe the parental origin and the mechanism of formation of a 46,X,der(X)(pter-->q21.1::p11.4-->pter)[23]/45,X[8] karyotype in a patient with mild Turner syndrome.

Design: Case report.

Setting: A university hospital.

Patient(s): A 23-year-old woman with normal height, gonadal dysgenesis, and mild Turner stigmata.

Intervention(s): Genotype-phenotype correlation, array-based copy number analysis, fluorescence in situ hybridization with locus-specific probes, and microsatellite marker-mediated haplotype analysis subsequent to whole genome amplification of microdissected chromosomes.

Main outcome measures: Genotype-phenotype correlation, mechanism of formation, and parental origin.

Result(s): Formation in paternal meiosis by refolding in itself and unequal recombination between Xp and Xq were found as the most likely mechanism of formation.

Conclusion(s): Formation of der(X) chromosomes in females can be more complex than previously thought. The nearly normal height of this patient could be explained by a combination of trisomy of the Xp-located SHOX gene and mosaicism with a 45,X cell line.