Pathogenesis (development of disease)
Individuals with Klinefelter syndrome have an extra X chromosome (47, XXY) in 80% of cases, which is due to nondisjunction during gametogenesis (germ cell development). In 20 % cases mosaic forms (mos 47, XXY /46, XY) are found, i.e. not the same karyotype (appearance of a chromosome set) is present in all cells. Furthermore, higher grade X chromosomal aneuploidies (48,XXY; 49,XXXXY), one or more additional Y chromosomes (e.g. 48,XXYY) and possibly structurally abnormal additional X chromosomes are found.
Numerical chromosomal abnormalities occur in about two thirds of cases in maternal oogenesis (development of oocytes) and in one third of cases in paternal spermatogenesis (development of spermatozoa).
The numerical chromosomal aberrations (hereditary alteration in the number of chromosomes) leads to primary hypogonadism (endocrine dysfunction of the testes), which results in disruption of Leydig cell function (→ disruption of testosterone production) and tubular function (→ disruption of spermatogenesis/spermatogenesis). As a result, there is decreased testosterone production and oligo- to azoospermia (oligozoospermia: sperm count < 15 million/milliliter; azoospermia: no sperm detectable).
Etiology (causes)
Biographic causes
- Genetic burden from parents, grandparents.
