10877 IUPAC Gold Book - Klinefelter syndrome 10.1351/goldbook.10877 10877 current 1 Syndrome in males resulting from a genetic defect in which an extra female X chromosome (thus an XXY genotype) is present in a male, characterized by small testes, long legs, enlarged breasts, reduced sperm production, and mental retardation. Syndrome https://goldbook.iupac.org/terms/view/11277 X chromosome https://goldbook.iupac.org/terms/view/11385 sperm https://goldbook.iupac.org/terms/view/11243 testes https://goldbook.iupac.org/terms/view/11295 PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 771 (https://doi.org/10.1515/pac-2015-1202) https://goldbook.iupac.org/terms/view/10877/html https://goldbook.iupac.org/terms/view/10877/json https://goldbook.iupac.org/terms/view/10877/plain Citation: 'Klinefelter syndrome' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.10877 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-06-14T01:19:59+00:00