A case report of rare XXY/XX mosaicism in a phenotypic male with Klinefelter syndrome and mediastinal germ cell tumor

Klinefelter syndrome (KS) is a common sex chromosome disorder and is characterized by small, firm testes with hyalinization of the seminiferous tubules, elevated gonadotropins and azoospermia. Among karyotypic variants of KS, mosaicism 47,XXY/46,XX is extremely rare. We report here a case of an 18-year-old boy with a mosaic 47,XXY/46,XX karyotype of peripheral blood diagnosed as KS. The boy presented with anterior mediastinal mass which was confirmed as combined carvenous lymphangioma and mixed germ cell tumor by histologic examination of resected tissue. He had the male phenotype, however, azoospermia was incidentally detected on sperm banking analysis, performed prior to chemotherapy for mixed germ cell tumor. He had small and firm testes, mild gynecomastia, collectively tanner stage IV, mild hypergonadotropic hypogonadism and no evidence of true hermaphroditism. This report presents a rare case of mosaicism 47,XXY/46,XX karyotype in a phenotypic male with KS and mediastinal germ cell tumors. Based on what we experienced and review of the literature, cytogenetic analysis is recommended when physicians are confronted with a young patient with mediastinal germ cell tumor.