Objectives.

There exist substantial differences between prenatally and postnatally diagnosed cases of 45,X/46,XY mosaicism. Ninety percent of prenatally diagnosed cases show a normal male phenotype, whereas the postnatally diagnosed cases show a wide spectrum of phenotypes. This 10% risk of an abnormal outcome in prenatally diagnosed cases requires further attention. The purpose of the present study is to provide more information on the postnatally diagnosed 45,X/46,XY mosaicism cases. To date, only a few series have been reported. An accurate diagnosis in these patients is essential not only to their follow-up, but also to providing appropriate genetic counselling and subsequent prenatal diagnosis to their parents.

Methods.

The clinical, cytogenetic, endocrinologic, histologic and molecular biological findings of 27 patients with 45,X/46,XY mosaicism are analyzed.

Results.

The reported cases showed a wide spectrum of phenotypes as Turner syndrome, mixed gonadal dysgenesis (MGD), male pseudohermaphroditism (MPH) and apparently normal male. However, Ulrich-Turner stigmata were the most common features found in this series. Patients with MGD or MPH presented with various degrees of sex reversal such as hypospadias and/or abnormal internal genitalia. No correlation between the proportion of the 45,X/46,XY cell lines in the blood or the fibroblasts and the phenotype was found. Mild mental retardation was present in 4 of the patients and 2 patients showed signs of autism.

Conclusions.

Two major points are emphasized in this series: 1) the presence in 7 histologically analyzed streak gonads of a homogeneous 45,X chromosomal complement suggests that the invasion of the primitive genital ridge by a such a cell line may induce abnormal gonadal development; 2) 3 males, apparently normal at birth, developed late onset abnormalities such as dysgenetic testes leading to infertility, Ulrich-Turner stigmata, dysmorphic features, and mild mental retardation. These data indicate the importance of an accurate clinical and histologic evaluation of any patient presenting with 45,X/46,XY mosaicism.

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