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.