[A patient with 46 XX/46 XY chimerism without hermaphroditism. The problem of prepuberal diagnosis of the Klinefelter's syndrome].

In a 12-year-old obese boy whose parents had asked for determination of sex chromatin the result was positive and Klinefelter's syndrome was diagnosed. Subsequently, the boy developed normally, went through puberty and presented with normal primary and secondary sex characteristics at the age of 22. The diagnosis was revised and on the basis of a karyotype the diagnosis of 46 XX/46 XY chimerism was made. In contrast to our patient, most dispermic chimeras are hermaphrodites. This case exemplifies the fact that Klinefelter's syndrome should not be diagnosed in prepubertal boys on the basis of positive sex chromatin.