49,XXXXY: a distinct phenotype. Three new cases and review

Over 100 cases of 49,XXXXY syndrome have been published to date. Classic findings include radioulnar synostosis, hypogonadism, and mental retardation. The majority of reported cases have not distinguished the 49,XXXXY syndrome from Klinefelter syndrome (47,XXY), and these patients are frequently labelled as having Klinefelter syndrome or as being a "Klinefelter variant." Because of distinct clinical features, we delineate the 49,XXXXY syndrome as separate from Klinefelter syndrome, and emphasise the prevalence of congenital heart defects. We also report three new cases of 49,XXXXY syndrome and briefly discuss patient management.