Prevalence; 1/600 and 1/700 male births (frequency increases with maternal age).The most common chromosomal anomaly in boys.

Often unrecognized because its clinical presentation is highly variable, the diagnosis may not be made until adolescence or adulthood.

Classic presentation:

-        hypogenitalism (small testicles) with sterility,

-        gynecomastia

-        sparse hair, female distribution pubic hair

-        tall stature

-        often impaired learning of language and reading, motor skills development.

Other comorbidities may be associated with the disease, and may become apparent in adulthood:

-        type 2 diabetes mellitus with metabolic syndrome (abdominal obesity with reduced lean body due to insufficient muscle development)

-        osteoporosis (10 %)

-        dental caries (18 %)

-        pectus excavatum with or without scoliosis, restrictive pulmonary syndrome

-        increased thromboembolic risk

-        chronotropic incompetence (= inability of the heart to increase its frequency in proportion to increased activity), mitral valve prolapse, short QT (especially in case of testosterone replacement therapy)

-        early atheromatosis

-        increased risk of psychiatric disorders ?

Anesthetic implications: 

behavioral abnormalities, fragile teeth, ECG (short QT ?), check blood sugar levels, thromboprophylaxis. One case of association with susceptibility to malignant hyperthermia.

References : 

-        Lee JY, Choi MH, Park JU.
Total intravenous anesthesia in a ma­lignant hyperthermia-susceptible patient with Klinefelter syn­drome undergoing orthognathic surgery.
J Craniofac Surg 2022; 33: e290-2.

-        Gaik C, Politt K.
A discussion of anesthesiologically relevant aspects of Klinefelter syndrome: a case report.
Korean J Anesthesiol 2025;78: 73-8.

Updated: March 2025