The prevalence and etiology of macro-growth hormone (GH)

Several macro-hormones have been reported to date. Among them, macroprolactinemia is a common cause of hyperprolactinemia. Growth hormone (GH) and prolactin (PRL) are anterior pituitary hormones related by structure and function. The aim of this study was to clarify the prevalence and etiology of macro-GH.

We examined the sera of 185 patients with high serum GH concentrations among 1,552 females who visited an obstetrics and gynecology hospital. The presence of macro-GH was investigated via the polyethylene glycol (PEG) method and gel filtration chromatography (GFC). Experiments using several reagents to block interfering substances in the serum with immunoassays and ¹²⁵I-GH tracers were performed to examine the nature of macro-GH.

PEG and GFC identified five patients with potential macro-GH, but four of them were due to the interference caused by human anti-rabbit IgG antibodies. One patient had true macro-GH due to anti-human GH autoantibody. The prevalence of macro-GH was 0.54 % (1/185) in patients with high serum GH concentrations. A ¹²⁵I-GH binding study revealed that this autoantibody significantly bound to human 22-kDa GH and 20-kDa GH but did not bind to the other human anterior pituitary hormones, rat GH or human chorionic gonadotropin. The affinity of the anti-GH autoantibody was 0.77 × 10⁸ M^-1 for 22-kDa GH and 0.71 × 10⁸ M^-1 for 20-kDa GH.

We presented a patient with macro-GH due to anti-human GH autoantibody. The prevalence of macro-GH was extremely rare compared to that of macro-PRL.