To determine whether men with Klinefelter syndrome (KS) have the same phenotype as men with mosaic KS.
Subject identification via prospectively collected database.
Male infertility specialty clinic.
Men undergoing a fertility evaluation from 2005 to 2012 at a single male infertility specialty clinic and having a karyotype demonstrating KS (mosaic or non-mosaic).
Testicular size, and semen and hormone parameters, genetic evaluation, and signs of testosterone (T) deficiency using validated questionnaires.
Of 86 men identified with KS, 6 (6.7%) were mosaic KS, and 80 (93.3%) were non-mosaic KS. Men with mosaic KS had lower baseline luteinizing hormone (LH) levels (10.31 IU/L ± 5.52 vs. 19.89 IU/L ± 6.93), lower estradiol levels (58.71 ± 31.10 pmol/L vs. 108.57 ± 43.45 pmol/L), larger mean testicular volumes (11 ± 7.3 mL vs. 6.35 ± 3.69 mL), and a higher mean total sperm count (4.43 ± 9.86 M/mL vs. 0.18 ± 1.17 M/mL). A higher proportion of men with mosaic KS had sperm in the ejaculate: 3 (50%) of 6 versus 3 (3.75%) of 80. The Sexual Health Inventory for Men (SHIM) and Androgen Deficiency in the Aging Male (ADAM) questionnaire scores were not different between groups.
Men with mosaic KS seem to be more well androgenized than their non-mosaic KS counterparts, both with respect to hormones and sperm in the ejaculate.