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. 1. Introduction Turner’s syndrome (TS) is one of the most common chromosomal abnormalities affecting 1 in 2500 newborn females [1]. It is characterized by short stature, gonadal dysgenesis, primary hypogonadism, congenital heart disease, renal anomalies, and a variety of somatic features [2]. TS was suggested to be due to absence of the second X chromosome in part or full [3]. The cytogenetic abnormality associated with TS was first described by Ford and coauthors in 1959 [4]. Since then, a variety of other karyotypic findings have been determined; classical 45,X is identified in about half of the patients, and the remaining half have either structurally abnormal sex chromosome, for example, 46,X,i(Xq) or are mosaic with other cell lines with normal (46,XX) or abnormal sex chromosomes [5]. In addition, a cell line containing the Y chromosome is present in 5% of patients, and further 3% of cases have an unidentifiable marker sex chromosome, presumably derived from a Y chromosome [6]. Y chromosome-specific SRY gene is one of the key genes involved in human sex determination. SRY gene encodes a testis specific transcription factor that plays a key role in sexual differentiation and development in males and is located on the distal region of the short arm of Y chromosome [7]. SRY expression initiates a network of gene activity that
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