title: Klinefelter syndrome and fertility: sperm preservation should not be offered to children with Klinefelter syndrome.
abstract: Should fertility preservation be offered to children with Klinefelter syndrome (KS)?
  
  
  
  Current evidence shows that fertility preservation should not be offered to adolescents with KS younger than 16 years because of lower retrieval rates for germ cells by testicular sperm extraction (TESE) compared with retrieval rates for adolescents and adults between 16 and 30 years.
  
  
  
  KS, the most common chromosomal disorder in men leading to non-obstructive azoospermia, is caused by the presence of at least one additional X chromosome. The onset of puberty in adolescents with KS leads to progressive degeneration of the testicular environment. The impact of the subsequent tissue degeneration on fertility potential of patients with KS is unknown, but in previous literature it has been suggested that fertility preservation should be started in adolescents as early as possible. However spermatozoa can be found by TESE in about 50% of adults with KS despite severe testicular degeneration. This review discusses the current evidence for fertility preservation in children and adolescents and possible prognostic markers for fertility treatment in KS.
  
  
  
  An extensive literature search was conducted, searching Pubmed, Embase, Cinahl and Web of Science from origin until April 2016 for 'Klinefelter syndrome' and 'fertility' and various synonyms. Titles and abstracts have been scanned manually by the authors for eligibility.
  
  
  
  In total 76 studies were found to be eligible for inclusion in this review. Information from the papers was extracted separately by two authors.
  
  
  
  Various studies have shown that pre-pubertal children with KS already have a reduced number of germ cells despite a normal hormonal profile during childhood. The presence of spermatozoa in the ejaculate of adolescents with KS is extremely rare. Using TESE, the retrieval rates of spermatozoa for adolescents younger than 16 years old are much lower (0-20%) compared with those for adolescents and young adults between 16 and 30 years old (40-70%). Although spermatogonia can be found by TESE in about half of the peri-pubertal adolescents, there are currently no clinically functional techniques for their future use. Children and adolescents need to be informed that early fertility preservation before the age of 16 cannot guarantee fertility later in life and may even reduce the chances for offspring by removing functional immature germ cells which may possibly develop into spermatozoa after puberty. Furthermore, except for the age of patients with KS, there are no identified factors that can reliably be used as a predictive marker for fertility preservation.
  
  
  
  Most of the evidence presented in this review is based on studies including a small number of adolescents with KS. Therefore, the studies may have been underpowered to detect clinically significant differences for their various outcomes, especially for potential predictive factors for fertility preservation, such as hormone levels. Furthermore, the population of patients with KS diagnosed during childhood might be different from the adult population with KS where the diagnosis is based on infertility. Results based on comparisons between the two groups must be interpreted with caution.
  
  
  
  Despite the limitations, this review summarizes the current evidence for managing fertility preservation in patients with KS to provide optimal health care.
  
  
  
  There was no funding for this study. S.F., Y.H., K.D., W.L.M.N., D.S., H.L.C.-v.d.G. and L.R. declare to have no conflicts of interests. D.D.M.B. reports grants from Merck Serono, grants from Ferring and grants from MSD, outside the submitted work. K.F. reports personal fees from MSD (commercial sponsor), personal fees from Ferring (commercial sponsor), grants from Merck-Serono (commercial sponsor), grants from Ferring (commercial sponsor) and grants from MSD (commercial sponsor), outside the submitted work.
authors.affiliation: Department of Obstetrics and Gynaecology, Radboudumc Nijmegen, Nijmegen, The Netherlands s.franik@radboudumc.nl.
authors.forename: S
authors.initials: S
authors.lastname: Franik
authors.affiliation: Department of Obstetrics and Gynaecology, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: Y
authors.initials: Y
authors.lastname: Hoeijmakers
authors.affiliation: Department of Urology, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: D'Hauwers
authors.affiliation: Department of Obstetrics and Gynaecology, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: D D M
authors.initials: DD
authors.lastname: Braat
authors.affiliation: Department of Obstetrics and Gynaecology, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: W L M
authors.initials: WL
authors.lastname: Nelen
authors.affiliation: Department of Genetics, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: D
authors.initials: D
authors.lastname: Smeets
authors.affiliation: Department of Pediatrics, Amalia Children's Hospital, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: H L
authors.initials: HL
authors.lastname: Claahsen-van der Grinten
authors.affiliation: Department of Obstetrics and Gynaecology, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Ramos
authors.affiliation: Department of Obstetrics and Gynaecology, Radboudumc Nijmegen, Nijmegen, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: Fleischer
mesh_terms: D000293:Adolescent; D000328:Adult; D005298:Fertility; D059247:Fertility Preservation / Q000379:methods*; D006801:Humans; D007713:Klinefelter Syndrome / Q000235:genetics*; D008297:Male; D012662:Semen Preservation; D012741:Sexual Maturation; D053625:Sperm Retrieval; D055815:Young Adult
keywords: Klinefelter syndrome; TESE; adolescent; fertility preservation; sperm retrieval