Epidemiology

Klinefelter syndrome (KS) is the most common male sex chromosome disorder, affecting around 1 in 660 males. This prevalence estimate is based on pooled data from several large studies involving chromosome analysis of newborns. However, the majority of affected individuals are never diagnosed, hence the diagnosed prevalence rate is significantly lower.[1][2]​

  • Data on the proportion of expected cases that are diagnosed varies between countries. In Denmark and the UK, it has been estimated that only around one quarter of affected individuals are diagnosed, whereas a study in Australia estimated a pick-up rate of 50%.[1][6]

The 2021 European Academy of Andrology guideline reports that among individuals who do receive a diagnosis of KS, 21% are diagnosed antenatally, 10% to 12% in pre-pubertal childhood, 16% at puberty, and 51% as adults.​[3]

  • The peak age range for diagnosis is the late-20s to mid-30s, with most cases picked up during evaluation for male infertility.[1][7]​​

  • Antenatal diagnosis is becoming increasingly common, via fetal anomaly screening.[3][4][8][9][10]​

There are few data on ethnic differences in prevalence, although one small US study suggested higher prevalence among males of Asian compared with white ethnicity.[4]​ 

Late diagnosis and non-diagnosis are both frequent, and individuals with more subtle clinical features often never receive a diagnosis. Ascertainment bias may therefore obscure the epidemiological picture and true morbidity and mortality may differ significantly from reported estimates.[4]​

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