Diabetes mellitus associated with Klinefelter's syndrome: a case report and review in Japan.

We report a case of Klinefelter's syndrome in a 48-year-old man who had diabetes mellitus associated with severe insulin resistance. We diagnosed him with Klinefelter's syndrome from his atrophic testicles, primary hypogonadism in hormonal examination, and a chromosomal aberration of 47,XXY. He showed severe decreased insulin sensitivity in a hyper-insulinemic euglycemic clamp test. He had injected over 100 units of insulin per day, however, testosterone replacement and administration of pioglitazone improved his glycemic control, which resulted in a decrease of insulin dose to less than 50 units per day. Here, we discuss the characteristics of diabetes mellitus associated with Klinefelter's syndrome in Japanese patients including this case.