<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A genetic disorder in males caused by having one or more extra X chromosomes. Males with this disorder may have larger than normal breasts, a lack of facial and body hair, a rounded body type, and small testicles. They may learn to speak much later than other children and may have difficulty learning to read and write. Klinefelter syndrome increases the risk of developing extragonadal germ cell tumors and breast cancer.</n0:def-definition><n0:def-source>NCI-GLOSS</n0:def-source></n0:ComplexDefinition><n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A SEX CHROMOSOME DISORDER characterized by small testes, underdevelopment of secondary sexual characteristics, infertility (INFERTILITY, MALE), hyalinization and fibrosis of the seminiferous tubules, and elevated levels of gonadotropin. Patients tend to have long legs and a slim, tall stature. GYNECOMASTIA is present in many of the patients. The classic form has the karyotype 47,XXY. Several variants include those with the karyotypes 48,XXYY; 48,XXXY; 49,XXXXY, and several mosaic patterns (46,XY/47,XXY; 47,XXY/48,XXXY, etc.).</n0:def-definition><n0:def-source>MSH2003_2003_05_12</n0:def-source></n0:ComplexDefinition><n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>genetic disease that produces sterile males with small testes lacking sperm due to XXY karyotype.</n0:def-definition><n0:def-source>CSP2003</n0:def-source></n0:ComplexDefinition>
<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A sex chromosome disorder caused by the presence of an extra X chromosome in the male karyotype. Affected individuals are infertile and have a small penis and testes. They tend to have tall stature and long legs and may have difficulties with speech and language development. Gynecomastia may be present.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>