RT Book, Section A1 Bianchi, Diana W. A1 Crombleholme, Timothy M. A1 D'Alton, Mary E. A1 Malone, Fergal D. SR Print(0) ID 1106402152 T1 47,XXY (Klinefelter Syndrome) T2 Fetology: Diagnosis and Management of the Fetal Patient, 2e YR 2015 FD 2015 PB McGraw-Hill Education PP New York, NY SN 978-0-07-144201-5 LK obgyn.mhmedical.com/content.aspx?aid=1106402152 RD 2024/03/29 AB Key PointsResults from meiotic nondisjunction that occurs in the sperm (44% of cases) or egg (56% of cases).About 10% of all cases are diagnosed prenatally and 26% of cases are diagnosed postnatally. The majority of cases are never diagnosed, which suggests that symptoms are mild.Incidence of 47, XXY is 1 in 500 to 1 in 800 male births. Incidence of 48, XXXY is 1 in 20,000.No sonographic findings are characteristic. Nuchal translucency measurement may be increased.The most significant factors regarding the decision whether or not to terminate the affected pregnancy are the presence of sonographic abnormalities and the medical specialty of the person providing the genetic counseling.Affected males are tall, but phenotypically normal, with an increased risk for developmental delays in speech, neuromotor, and learning disabilites.Testosterone treatment is recommended, beginning at puberty.50% to 80% of affected males develop gynecomastia, but it is usually mild.Fertility is now possible with assisted reproductive technology.Motor impairment and speech and language problems are more common if the extra X chromosome is paternally derived.