Klinefelter se sindroom klinefelters syndrom Klinefelter syndrome Klinefelters syndrome 48,XXYY syndrome http://purl.bioontology.org/ontology/MEDDRA/10048230 http://purl.bioontology.org/ontology/SNOMEDCT/205699007 https://en.wikipedia.org/wiki/XXYY_syndrome https://www.wikidata.org/wiki/Q8042649 48, XXYY syndrome A sex chromosome anomaly in which males have an extra X and Y chromosome. Human cells usually contain two sex chromosomes, one from the mother and one from the father. Usually, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The appearance of at least one Y chromosome with a properly functioning SRY gene makes a male. Therefore, humans with XXYY are genotypically male. Males with XXYY syndrome have 48 chromosomes instead of the typical 46. It affects an estimated one in every 18,000–40,000 male births. Klinefelter syndrome, XXYY Klinefelter's syndrome, XXYY XXYY syndrome 48,XXYY