الفهرس 
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Abstract
TS is the most common chromosomal abnormality in females, affecting 1:2,000 live female birth. It is characterized by short stature, gonadal dysgenesis and a variety of somatic features and major organ malformations. About 50% of the patients have a 45,X karyotype, while the remainder have structurally abnormal sex chromosomes or mosaicism including XX/XY. Cytogenetic technique detects Y chromosome mosaicism in about 5.5% of TS. FISH with X and Y centromere probes should be used to search for hidden mosaicism and it may be necessary to test two to three tissues to exclude cryptic Y material; FISH of buccal cells may detect Y mosaicism that is not detectable in peripheral blood. Those with Y chromosomal material are at increased risk for developing gonadoblastoma, which has considerable malignant potential. Currently, it is recommended to perform prophylactic gonadectomy in TS patients with Y-chromosome material.
The aim of this study was to determine the value of additional genetic studies as FISH and the inclusion of a second tissue (buccal cells) in search for mosaicism in TS patients with apparent complete 45,X karyotype, as well as, identifying the origin of marker chromosome in TS patients with 46,X,+mar on standard lymphocyte karyotyping.
The study was carried out on twenty patients with TS. AlCl cases were subjected to careful history taking, complete clinical examination, abdominal and pelvic sonography, hormonal assays, cytogenetic examination, FISH using X and Y probes on both blood culture and buccal cells. Lastly patients and their families were offered proper genetic counseling.
Examination of studied cases revealed that TS was characterized by short stature in 75 % of cases, gonadal hypoplasia in 100% of cases and a variety of somatic features as neck webbing in 75% of cases, short fourth and fifth metacarpals in 75% of cases and, cubitus valgus in 55% of cases. Cardiac and renal anomalies were reported in 25% and 20% of the studied patients respectively.
FISH study was conducted on 20 patients using two tissues; blood culture and buccal tissue. Twenty percent of patients had a cell line containing Y material, forty percent had variable degrees of X, XX mosaicism, and the remaining forty percent no second cell line was detected.
FISH study helped identify the origin of marker to be Y in all patients as well as identifying cryptic mosaicism with X and Y cell lines in 60% of the studied patients. The introduction of an additional cell line as buccal cells helped identifying mosaicism in a patient with monosomy X in both karyotype and blood FISH.
Clinical correlation with FISH result showed that monosomy X patients had the most severe phenotype, and virilization signs appeared only with patients having Y containing cell line.