Achondrogenesis type 2 (ACG2), a form of achondrogenesis (see this term), is a very rare and lethal skeletal dysplasia and part of the spectrum of type 2 collagen-related bone disorders (see this term), characterizedby severe micromelia, short neck with large head, small thorax, protuberant abdomen, underdeveloped lungs, distinctive facial features such as a prominent forehead, a small chin, a cleft palate (in some) and distinctive histological features of the cartilage.