| Enrolling By Invitation | Long-term Systematic Follow-up of Patients With Klinefelter Syndrome Followed at the Department of Growth and NCT07142135 | Rigshospitalet, Denmark | — |
| Not Yet Recruiting | Growing up With the Young Endocrine Support System (YESS!) NCT04252001 | dr. Laura C. G. de Graaff-Herder | N/A |
| Recruiting | Klinefelter Syndrome and Testosterone Treatment in Puberty NCT06294990 | Lise Aksglæde | Phase 4 |
| Unknown | Sex Steroids Balance for Metabolic and Reproductive Health in Klinefelter Syndrome NCT05586802 | Georgios Papadakis | Phase 3 |
| Active Not Recruiting | Interrogating Fatty Acid Metabolism Impairment and Clinical Correlates in Males with Klinefelter Syndrome NCT05498090 | University of Colorado, Denver | Phase 4 |
| Unknown | Endocrine, Metabolic, Cardiovascular and Immunological Aspects of Sex Chromosome Abnormalities in Relation to NCT05425953 | University of Aarhus | — |
| Enrolling By Invitation | Parent and Infant Inter(X)Action Intervention (PIXI) NCT03836300 | RTI International | N/A |
| Unknown | Turner And Klinefelter Treatment Target Study NCT04803474 | dr. Laura C. G. de Graaff-Herder | — |
| Unknown | Unraveling the Klinefelter's Disease Physiopathology NCT05997706 | Cliniques universitaires Saint-Luc- Université Catholique de Louvain | N/A |
| Completed | TESTO: Testosterone Effects on Short-Term Outcomes in Infants With XXY NCT03325647 | University of Colorado, Denver | Phase 4 |
| Recruiting | The eXtroardinarY Babies Study: Natural History of Health and Neurodevelopment in Infants and Young Children W NCT03396562 | University of Colorado, Denver | — |
| Completed | Cardiometabolic Profiles of Boys With Klinefelter Syndrome NCT02723305 | University of Colorado, Denver | — |
| Terminated | Fertility Assessment in Patients With Klinefelter Syndrome NCT02461303 | University of Pittsburgh | — |
| Completed | Expanded Noninvasive Genomic Medical Assessment: The Enigma Study NCT02787486 | Progenity, Inc. | — |
| Completed | Thrombosis and Neurocognition in Klinefelter Syndrome NCT02526628 | University of Aarhus | — |
| Completed | Body Composition in Infants With Klinefelter Syndrome and Effects of Testosterone Treatment NCT02408445 | University of Colorado, Denver | Phase 4 |
| Unknown | Whole Blood Specimen Collection From Pregnant Subjects NCT02430584 | Progenity, Inc. | — |
| Completed | Sperm Production in Kleinfelter Syndrome Patients After Mesenchymal Stem Cell Injection NCT02414295 | Man Clinic for Andrology, Male Infertility and Sexual Dysfunction | N/A |
| Completed | Klinefelter Fertility Preservation NCT01817296 | Boston Children's Hospital | N/A |
| Completed | TyG Index Levels in Klinefelter Syndrome NCT05014997 | Gulhane School of Medicine | — |
| Completed | X-chromosome Inactivation, Epigenetics and the Transcriptome NCT01678261 | University of Aarhus | — |
| Completed | Life Quality and Health in Patients With Klinefelter Syndrome NCT01690013 | University of Aarhus | — |
| Completed | Study of Psychological and Motor Effects of Testosterone in Adolescents With XXY/Klinefelter Syndrome NCT01585831 | University of Colorado, Denver | N/A |
| Completed | Human Chorionic Gonadotropin Stimulation Effects on Steroidogenesis in Men With Klinefelter Syndrome NCT02788136 | Azienda USL Modena | N/A |
| Completed | Fertility Preservation in Cases of Klinefelter Syndrome. NCT01918280 | Hospices Civils de Lyon | N/A |
| Completed | Subcapsular Orchiectomy in Men With Klinefelter Syndrome NCT01750632 | Odense University Hospital | N/A |
| Completed | Neuropsychologic, Neuroradiologic, Endocrinologic, and Genetic Aspects of Klinefelter Syndrome NCT00999310 | University of Aarhus | — |
| Completed | Androgen for Leydig Cell Proliferation NCT01206270 | University of Roma La Sapienza | Phase 2 / Phase 3 |
| Completed | Adaptation Among Adolescents and Adults With Klinefelter Syndrome NCT00896272 | National Human Genome Research Institute (NHGRI) | — |
| Recruiting | Thyroid Function and Structure in Klinefelter Syndrome NCT05581147 | University of Roma La Sapienza | — |
| Completed | Androgen Effect on Klinefelter Syndrome Motor Outcome NCT00348946 | Thomas Jefferson University | Phase 2 |
| Withdrawn | Adaptive Behavior Assessment of Men With 49, XXXXY, Klinefelter Syndrome NCT00347464 | University of Wisconsin, Madison | — |
| Completed | Body Composition, Bone Mineral Density, Insulin Sensitivity and Echocardiographic Measurements in Klinefelter NCT00523835 | University of Aarhus | — |