Characterized by an abnormal number of X chromosomes (80% with 47XXY) and primary gonadal insufficiency.
Frequency: 1/1000-1400 live male births; 1/100 patients in mental institutions; and 3.4/100 infertile men.
Eunuchoid appearance with increased stature and small to normal-sized, well developed testes.
Mental retardation, speech difficulties.
Small hyalinized seminiferous tubules.
Pseudoadenomatous clusters of Leydig cells – these cells only appear to be increased in number, though, because the decreased testicular volume.
Associations: increased incidence of extragonadal germ cell tumors (mediastinum>pineal gland, CNS, retroperitoneum) as well as hypopituitarism.