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.
Source: 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)