Effect of ascertainment and genetic features on the phenotype of Klinefelter syndrome

J Pediatr. 2008 May;152(5):716-22. doi: 10.1016/j.jpeds.2007.10.019. Epub 2007 Dec 21.


Objective: To describe the Klinefelter Syndrome (KS) phenotype during childhood in a large cohort.

Study design: Clinical assessment, measurement of hormonal indices of testicular function, and parent of origin of extra X chromosome were assessed in a cross-sectional study of 55 boys with KS, aged 2.0 to 14.6 years, at an outpatient center.

Results: Mean height and body mass index SD scores (SDS +/- SD) were 0.9 +/- 1.3 and 0.4 +/- 1.4, respectively. Mean penile length and testicular volume SDS were -0.5 +/- 0.9 and -0.9 +/- 1.4. Testosterone levels were in the lowest quartile of normal in 66% of the cohort. Other features included clinodactyly (74%), hypertelorism (69%), elbow dysplasia (36%), high-arched palate (37%), hypotonia (76%), and requirement for speech therapy (69%). Features were similar in boys in whom the diagnosis was made prenatally versus boys in whom the diagnosis was made postnatally. There was no evidence for a phenotypic effect of parent of origin of the extra X chromosome.

Conclusions: Boys with KS commonly have reduced penile length and small testes in childhood. The phenotype in boys with KS does not differ according to ascertainment or origin of the extra X chromosome. Boys with KS may be identified before puberty by tall stature, relatively decreased penile length, clinodactyly, hypotonia, and requirement for speech therapy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Age Factors
  • Body Weights and Measures
  • Child
  • Child, Preschool
  • Cohort Studies
  • Cross-Sectional Studies
  • Gonadal Hormones / blood
  • Gonadotropins / blood
  • Humans
  • Klinefelter Syndrome / blood
  • Klinefelter Syndrome / genetics*
  • Klinefelter Syndrome / pathology*
  • Male
  • Phenotype


  • Gonadal Hormones
  • Gonadotropins