pediatrics
Klinefelter Syndrome (47,XXY)
Introduction
Klinefelter syndrome is the presence of two or more X chromosomes plus one Y, resulting in a phenotypic male. Diagnosis is based on clinical findings and is confirmed by cytogenetic analysis. Treatment may includetestosteronesupplementation. (See also Overview of Chromosomal Abnormalities .) Klinefelter syndrome is the most common Overview of Sex Chromosome Abnormalities . Reported prevalence varies, and it is likely underdiagnosed (a national database study reported 6/10,000 male live births) ( Affected boys tend to be tall with disproportionately long arms and legs. They often have small, firm testes, and approximately 30% develop Gynecomastia . Puberty usually occurs at the normal age, but often facial hair growth is light. There is a predisposition for verbal learning disorders. Clinical variation is great, and many 47,XXY males have normal appearance and intellect. Testicular development varies from hyalinized nonfunctional tubules to some production of spermatozoa; urinary excretion of follicle-stimulating hormone is frequently increased. Men with Klinefelter syndrome tend to develop Diabetes Mellitus (DM) , chronic lung disease, Mosaicism occurs in approximately 15% of cases. Males with a normal male karyotype (XY) in some cells may be fertile and have less obvious malformations. Some affected men have 3, 4, and even 5 X chromosomes along with the Y. As the number of X chromosomes increases, the severity of intellectual disability and of malformations also increases. Each extra X is associated with a 15- to 16-point reduction in IQ, with language most affected, particularly expressive language skills. 