Trisomy Xq in a male: the isochromosome X Klinefelter syndrome.

We report on a male with trisomy Xq resulting from an isochromosome Xq which is preferentially inactivated: 47,XY,+i(Xq). Six previous cases have been reported. These patients are similar to patients with classical Klinefelter syndrome (47,XXY) in that they have infertility, decreased masculinization, gynecomastia, and elevated luteinizing hormone (LH) and follide stimulating hormone (FSH) levels. They may differ in having average intelligence and normal to short stature. These findings indicate that extra copies of the long arm of X have phenotypic expression, even though activated only in early development.