Klinefelter syndrome is the most common sex chromosome disorder and a common cause of primary hypogonadism. This congenital syndrome is seen in males with at least 1 additional X chromosome. While the majority of cases are caused by the 47,XXY karyotype, other karyotypes have also been identified. The presence of additional X chromosome(s) is responsible for testicular dysfunction and other clinical features, including signs and symptoms of androgen deficiency, increased height, and psychosocial abnormality. Phenotypical expression is variable, and the condition is thought to be underdiagnosed with only 40% of cases reported. Of note, Klinefelter syndrome is associated with increased mortality and morbidity from a variety of co-morbidities.
ICD10CM: Q98.1 – Klinefelter syndrome, male with more than two X chromosomes
SNOMEDCT: 22053006 – Klinefelter syndrome
Differential Diagnosis & Pitfalls
47,XYY syndrome (Jacob syndrome) – Another underdiagnosed sex chromosomal disorder. Males are tall and have developmental abnormalities, incoordination, and ulceration of legs. Distinguishing physical features include large teeth, radioulnar synostosis, clinodactyly, and tremor. Patients are usually fertile and have normal pubertal development.