May have a small phallus, gynecomastia, and some degree of eunuchoid proportions (due to delayed epiphyseal fusion).
Hormonal Changes
↑ LH and ↑ FSH (due to primary testicular failure).
↓ Testosterone, variable increases in estradiol → risk of gynecomastia.
Spectrum of Masculinization
Ranges from moderate eunuchoidism to near-normal male phenotype.
Gynecomastia severity is highly variable.
Histology
Seminiferous tubules show thickened basement membranes, sclerosis, and hyalin deposits.
Leydig cells may be clumped or increased in number; can form adenoma-like nests.
Before adolescence, testes may appear near-normal pathologically.
Other Clinical Issues
Typically no multiple congenital anomalies (unlike Turner syndrome).
Mild mental impairment or learning disabilities (especially verbal) can occur.
Increased psychosocial and behavioral difficulties (anxiety, depression, poor judgment).
Higher risk for pulmonary disorders (emphysema, bronchiectasis), certain cancers (mediastinal germ cell tumors, breast cancer), diabetes mellitus, and varicose veins.
46,XX Male Variant
Similar phenotype to Klinefelter but often with hypospadias and shorter stature.
Arises from translocation of SRY to the X chromosome.
47,XYY Karyotype**
Phenotypically normal males, usually fertile, typically normal testicular function.
May have increased risk of speech/language developmental delays and learning disabilities.
Diagnosis
Clinical Suspicion
Tall adolescent/adult male with small firm testicles, gynecomastia, infertility.
Often presents with delayed or incomplete puberty.
Laboratory Findings
Karyotype of peripheral leukocytes confirms extra X material (e.g., 47,XXY).
