title: 48,XXYY, 48,XXXY and 49,XXXXY syndromes: not just variants of Klinefelter syndrome.
abstract: Sex chromosome tetrasomy and pentasomy conditions occur in 1:18,000-1:100,000 male births. While often compared with 47,XXY/Klinefelter syndrome because of shared features including tall stature and hypergonadotropic hypogonadism, 48,XXYY, 48,XXXY and 49,XXXXY syndromes are associated with additional physical findings, congenital malformations, medical problems and psychological features. While the spectrum of cognitive abilities extends much higher than originally described, developmental delays, cognitive impairments and behavioural disorders are common and require strong treatment plans. Future research should focus on genotype-phenotype relationships and the development of evidence-based treatments.
  
  
  CONCLUSIONS
  The more complex physical, medical and psychological phenotypes of 48,XXYY, 48,XXXY and 49,XXXXY syndromes make distinction from 47,XXY important; however, all of these conditions share features of hypergonadotropic hypogonadism and the need for increased awareness, biomedical research and the development of evidence-based treatments.
authors.affiliation: Section of Neurodevelopmental Behavioral Pediatrics, Department of Pediatrics, University of Colorado School of Medicine, Aurora, USA. Tartaglia.nicole@tchden.org
authors.forename: Nicole
authors.initials: N
authors.lastname: Tartaglia
authors.forename: Natalie
authors.initials: N
authors.lastname: Ayari
authors.forename: Susan
authors.initials: S
authors.lastname: Howell
authors.forename: Cheryl
authors.initials: C
authors.lastname: D'Epagnier
authors.forename: Philip
authors.initials: P
authors.lastname: Zeitler
mesh_terms: D006801:Humans; D007006:Hypogonadism / Q000235:genetics; D007713:Klinefelter Syndrome / Q000175:diagnosis / Q000235:genetics* / Q000523:psychology; D008297:Male; D010641:Phenotype; D025064:Sex Chromosome Disorders / Q000175:diagnosis / Q000235:genetics* / Q000523:psychology; D013577:Syndrome