In humans, it has two major forms: a-CGRP, primarily involved in migraine (see below), which is mainly expressed in primary sensory neurons of the dorsal root ganglia, throughout the trigeminal system (located on Adelta-fibers and Cfibers) and in vagal ganglia; and b-CGRP, which is found mainly in intrinsic enteric gray neurons. The gene discussed is CALCA; the disease is migraine disorder.