Editor—Turner syndrome is one of the most common chromosomal abnormality syndromes affecting 1 in 2500 liveborn females. The syndrome is characterised by short stature, gonadal dysgenesis, congenital heart disease, renal anomalies, and a variety of somatic features including neck webbing, cubitus valgus, short neck, and widely set nipples. Nearly half of the patients have a classical 45,X karyotype while others have structurally abnormal sex chromosomes (for example, 46,X,i(Xq)) or are mosaics with other cell lines with normal (46,XX) or abnormal sex chromosomes.1-4 Among these, patients with Y chromosomal material require specific attention since many of these 45,X/46,XY Turner syndrome patients develop gonadoblastoma or dysgerminoma later in life.5 6

Conventional chromosomal analysis indicates that 4-20% of patients with Turner syndrome have a Y chromosome or its derivatives.1-4 These figures could be even higher, since the more sensitive PCR based analysis has shown that 15-60% of cytogenetically 45,X females have Y chromosomal material.7-9 These findings mean that 10-50% of all Turner syndrome patients have Y chromosomal material and therefore are, to some extent, at risk of developing gonadoblastoma. A more precise understanding of the mechanism leading to generation of a 45,X/46,XY karyotype is therefore important for providing better care for these patients.

Karyotypes such as 45,X/46,XY are presumably caused by mitotic loss of the Y chromosome from the originally 46,XY fetus. It is not known, …