Please help? Is the disease gigantism a dominant or recessive gene?

Neither. Pituitary gigantism results from a pituitary adenoma, an acquired tumor. There are a few dozen genetic syndromes in which a person may be extra-tall; common Marfan's is a dominant; there's a dominant family syndrome in which people are prone to get pituitary gigantism; there's at least one rare autosomal recessive with gigantism with multiple birth defects.