Gigantism Gigantism is a growth defect that occurs during childhood, from over exposure to growth hormone. The condition of the constant growth can be on the whole body or parts of the body. This particular diagnose is most common in the children which then extends it self to the teenage years. Basically it occurs before puberty. Gigantism is caused by oversecretion of human growth hormone (hGH), which has the ability to produce changes throughout the body. Tumors like somatotrophe adenomas, extrapyradimal pituitary lesions or other tumors may cause this oversecretion, but what exactly causes these tumors is yet to be determined.