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Open access

Lukas Ochsner Ridder, Agnethe Berglund, Kirstine Stochholm, Simon Chang, and Claus H Gravholt


Klinefelter syndrome (KS, 47,XXY) and 47,XYY syndrome are genetic conditions characterized by a supernumerary sex chromosome. The conditions share many traits, but considerable phenotypic differences are seen between the two. Focusing on morbidity, mortality, and socioeconomics, this review highlights similarities and differences.


Relevant literature was identified through PubMed with the following search terms; 'Klinefelter', '47,XXY', '47,XYY', and 'Jacobs syndrome'. Included journal articles were chosen at the authors’ discretion.


KS and 47,XYY are the most common sex chromosome disorders in males, with an expected prevalence of 152 and 98 per 100,000 newborn males, respectively. Non-diagnosis is extensive, as only about 38% of KS and 18% of 47,XYY are diagnosed. Both conditions are associated with an increased mortality risk and increased risk of a variety of diseases and other health-related problems affecting virtually every organ system. Early diagnosis seems to predict a lesser comorbidity burden. Neurocognitive deficits as well as social and behavioral problems are commonly described. Both syndromes are associated with poor socioeconomicfor example, lower income and educational level and higher rates of crime. Infertility is a hallmark of KS, but fertility seems also reduced in 47,XYY.


Being born as a boy with an extra X or Y chromosome is associated with increased mortality and excess morbidity, partially expressed in a sex chromosome-specific pattern.Both syndromes continue to be greatly underdiagnosed, even thoughearly intervention may improve the overall outcome. Earlier diagnosis to initiate timely counseling and treatment should be emphasized.

Open access

Simon Chang, Christian Fynbo Christiansen, Anders Bojesen, Svend Juul, Anna-Marie B Münster, and Claus H Gravholt


Klinefelter syndrome (KS), 47,XXY, can be viewed as a disease model for investigating the risk of thrombosis in male hypogonadism and the subsequent risk related to testosterone treatment. We describe rates of thrombotic risk factors, thrombosis and thrombosis mortality in KS and the association with testosterone treatment.


National registry-based matched cohort study with follow-up from 1995 to 2016 set in Denmark. For the study, 1155 men with KS were each matched by year and month of birth to 100 men from the background population. First thrombotic events and thrombosis mortality was evaluated by event rates and hazard ratios (HRs) and by applying testosterone treatment as a time-dependent covariate.


The KS cohort had higher incidence of venous thromboembolism relative to the comparison cohort (HR, 3.95; 95% CI, 2.83–5.52). Total thrombotic deaths were increased in KS (HR, 1.76; 95% CI, 1.18–2.62), and all-cause mortality was increased in KS following arterial thrombosis (HR 1.73; 95% CI 1.22–2.47). Only 48.7% of men with KS redeemed prescriptions for testosterone. Untreated men with KS were on average born 12 years before those treated, and the majority of untreated men with KS with available biochemistry were hypogonadal. Testosterone treatment in KS was associated with a non-significant decrease in venous thromboembolism and thrombotic deaths.


Thrombosis and thrombotic deaths are increased in KS. Only half of the men with KS ever received testosterone treatment, despite overt hypogonadism in the non-treated. Testosterone treatment in Klinefelter syndrome was insignificantly associated with lower incidence rates of venous thrombosis and thrombotic deaths.

Open access

Simon Chang, Arkadiusz J Goszczak, Anne Skakkebæk, Jens Fedder, Anders Bojesen, M Vakur Bor, Moniek P M de Maat, Claus H Gravholt, and Anna-Marie B Münster


Klinefelter syndrome (KS) is associated with increased risk of thrombosis. Hypogonadism and accumulating body fat in KS have a potential impact on fibrinolysis. In this study, we assessed the fibrinolytic system and the association with testosterone levels in KS.


This study is a cross-sectional comparison of men with KS and age-matched male controls.


Fibrin clot lysis was evaluated by turbidity measurements and by measuring levels of individual fibrinolytic proteins in plasma samples. Fibrin clot structure was evaluated by scanning electron microscopy. Total testosterone was measured by liquid chromatography-tandem mass spectrometry. Body fat was evaluated by dual-energy X-ray absorptiometry.


In this study, 45 men with KS and 45 age- and education-matched controls were included. Men with KS had a 24% reduction in fibrin clot lysis compared with controls (46.2 ± 17.1 vs 60.6 ± 18.8 %/h, P  = 0.0003) and higher levels of fibrinogen, factor XIII (P ≤ 0.01), and plasminogen activator inhibitor type 1 (P  = 0.04). Men with KS had lower total testosterone (P  = 0.008) and higher body fat (P  = 0.001). In KS, reduced fibrin clot lysability was associated with higher fibrinogen and body fat related to decreasing total testosterone and hypogonadism among men with KS. Fibrin clot structure was not different compared to KS and controls.


Fibrin clot lysis in KS was markedly reduced, potentially contributing to a prothrombotic state and increasing thrombotic risk. Hypogonadism in KS was associated with increased fibrinogen and total body fat, predicting reduced fibrin clot lysis.