Klinefelter syndrome

https://doi.org/10.1351/goldbook.10877

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 [Terms] [Paper]