I've written a fair bit about acromegaly in the past - caused by a pituitary tumour secreting high levels of growth hormone, it can lead to gigantism if it occurs in childhood. But you may not have heard of pituitary dwarfism, which is effectively the opposite of acromegaly - although there's usually no tumour involved - in which the pituitary gland fails to secrete enough growth hormone. If a child with pituitary dwarfism is left untreated, this can lead to permanently stunted growth.
Recently the world's tallest man, Sultan Kosen, has been in the news; his growth, caused by a pituitary adenoma, has finally been brought under control after surgery and medical treatment. Even so, he stands over 8 feet tall. In contrast, Special Olympics athlete Mackenzie MacDonald who has also been in the news was successfully treated for her childhood pituitary dwarfism, attaining a height of 5'4".