Analysis of the SRY gene in Turner syndrome patients with Y chromosomal material

The Use of Fluorescence In situ Hybridisation in the Diagnosis of Hidden Mosaicism in Egyptian Patients with Turner Syndrome

Background

Turner syndrome (TS) is the most common chromosomal abnormality in females. The diagnosis of TS is based on karyotyping of 30 blood lymphocytes. This technique does not rule out tissue mosaicism or low-grade mosaicism in the blood. Because of the associated risk of gonadoblastoma, mosaicism is especially important in case this involves a Y chromosome.

Aims

This study was set to determine the value of additional genetic studies such as fluorescent in situ hybridisation and the inclusion of buccal cells in search for mosaicism in TS patients.

Settings and Design

This cross-sectional, descriptive study was performed in Human Genetics Department, Medical Research Institute, Alexandria University.

Materials and Methods

Fluorescence in situ hybridisation technique was applied to lymphocyte cultures as well as buccal smears using centromeric probes for X and Y chromosomes. Genotype phenotype correlation was also evaluated.

Statistical Analysis Used

Descriptive study where categorical variables were described using number and percentage and continuous variables were described using mean and standard deviation.

Results

Fluorescence in situ hybridisation technique study detected hidden mosaicism in 60% of studied patients; 20% of patients had a cell line containing Y material, while 40% had variable degrees of X, XX mosaicism, and in the remaining 40% no second cell line was detected. Fluorescence in situ hybridisation study helped identify the origin of the marker to be Y in all patients. The introduction of an additional cell line helped in identifying mosaicism in patients with monosomy X. Virilisation signs were only observed among TS patients with Y cell line mosaicism. The clinical manifestations were more severe in patients with monosomy X than other mosaic cases.

Conclusions

Molecular cytogenetic investigation for all suspected cases of TS should be considered for appropriate treatment plan and genetic counselling.

Hidden Y Chromosome Mosaicism in 48 Egyptian Patients with Turner’s Syndrome

Background. The presence of Y chromosome material in Turner's syndrome (TS) patients is a risk factor for the development of gonadoblastoma. Although conventional cytogenetic analysis is the definitive diagnosis of TS, low level Y chromosome mosaicism may be missed. Molecular analysis has demonstrated a higher proportion of mosaicism, but there is controversy regarding the prevalence of Y chromosome-derived material in those patients. Aim and Methods. This study was conducted to investigate the prevalence of hidden Y chromosome mosaicism in 48 TS Egyptian patients using polymerase chain reaction (PCR) for molecular DNA analysis of SRY gene and compare our results with those in the literature. Results. None of TS patients had a cytogenetically obvious Y chromosome; Y chromosome material was detected only at molecular analysis. SRY gene was found in 9 TS patients (18.75%) with the classical 45,X karyotype, whereas all other patients were SRY negative. Conclusion. Cytogenetically undetected Y chromosome mosaicism is common in TS patients; these data reinforce the need for adequate diagnosis of Y chromosome material in those patients. Molecular screening for Y chromosome-derived DNA should be routinely carried out in all TS patients.

Paternally derived der(7)t(Y;7)(p11.1 approximately 11.2;p22.3)dn in a mosaic case with Turner syndrome

An unusual mosaic karyotype was detected in a 6-year-old female patient with clinical diagnosis of Turner syndrome (TS). Cytogenetic and molecular cytogenetic studies revealed besides a cell line with 45,X a second cell line where the short arm of the Y-chromosome was translocated onto the short arm of a chromosome 7; karyotype: 45,X,der(7)t(Y;7)(p11.1 approximately 11.2;p22.3)/45,X. To delineate the mechanisms of rearrangement and karyotypic evolution in this case, further studies were performed. A maternal origin of the X-chromosome and biparental origin of both chromosomes 7 were determined by microsatellite analysis. Furthermore, using parental-origin-determination fluorescence in situ hybridization (pod-FISH) it could be established that the derivative chromosome 7 was of paternal origin. Overall, this is to the best of our knowledge the first report of such a complex mosaic TS karyotype.