Reply to correspondence from Hall??Detection of Y-specific sequences in patients with Turner syndrome?

Detection of low level sex chromosome mosaicism in Ullrich–Turner syndrome patients

Ullrich-Turner syndrome (UTS) is most commonly due to a 45,X chromosome defect, but is also seen in patients with a variety of X-chromosome abnormalities or 45,X/46,XY mosaicism. The phenotype of UTS patients is highly variable, and depends largely on the karyotype. Patients are at an increased risk of gonadoblastoma when a Y-derived chromosome or chromosome fragment is present. Since constitutional mosaicism is present in approximately 50% of UTS patients, the identification of minor cell populations is clinically important and a challenge to laboratories. We identified 50 females with a 45,X karyotype as the sole abnormality or as part of a more complex karyotype. Twenty two (44%) had a 45,X karyotype; mosaicism for a second normal or structurally abnormal X was observed in 24 (48%) samples, and mosaicism for Y chromosomal material in 4 (8%) cases. To further investigate the possibility of mosaicism in the 22 patients with an apparently non-mosaic 45,X karyotype, we performed FISH using centromere probes for the X and Y chromosomes. A minor XX cell line was identified in 3 patients, and the 45,X result was confirmed in 19 samples. No samples with XY mosaicism were identified. We describe our validation process for a FISH assay to be used in clinical practice to identify XX or XY mosaicism. FISH as an adjunct to karyotype analysis provides a sensitive and cost-effective technique to identify sex chromosome mosaicism in UTS patients.

FISH analysis helps identify low-level mosaicism in Ullrich-Turner syndrome patients

PURPOSE

To search for X or Y chromosome mosaicism in 45,X individuals using fluorescent in situ hybridization (FISH).

METHODS

From our series of 53 Ullrich-Turner syndrome patients, we used interphase FISH to evaluate the 19 who had an apparently nonmosaic 45,X karyotype with G-banding.

RESULTS

Of those 19 patients, mosaicism was detected in seven (37%), five patients had an XX line, one had a monocentric isochromosome X, and one had a dicentric isochromosome X. No Y chromosome mosaic was identified.

CONCLUSION

FISH analysis is a sensitive and cost-effective adjunct to karyotype analysis to identify sex chromosome mosaicism in UTS.