Disease states of GH excess (e.g., acromegaly) and GH deficiency (GHD) (e.g., congenital isolated GHD) are characterized by increased and decreased GH and IGF-I levels, where the GH/IGF-I relationship is reflected by a “primary association” (high GH and high IGF-I for acromegaly and low GH and low IGF-I for GHD). The gene discussed is IGF1; the disease is acromegaly.