Ovarian hyperstimulation syndrome (OHSS) is usually a complication of assisted reproductive techniques, more rarely an affection complicating a spontaneous gestation. The cause of hyper responsiveness of ovaries to the gonadotropins used in the controlled stimulation is still largely unknown. In contrast, a few cases of spontaneous hyperstimulation syndrome have been elucidated by the identification of mutations of the follicle-stimulating hormone (FSH) receptor, broadening its specificity and making it hypersensitive to human chorionic gonadotropin (hCG). Surprisingly, the mutations were located in the transmembrane domain of the receptor rather than in the extracellular hormone-binding site. No such mutation has been found in iatrogenic cases. However, allelic variants of the FSH receptors have been associated with the response to FSH in stimulation procedures, as well as with the severity of OHSS when present.
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