In humans, dwarfism is sometimes defined as an adult height of less than 4 feet 10 inches (58 in; 147 cm). Dwarfism can be caused by more than 300 distinct medical conditions. In cases of proportionate dwarfism, the body appears normally proportioned, but is unusually small. The main reason for Dwarfing conditions are frequently referred to as short-limb or short-trunk types. Achondroplasia, hypochondroplasia, and metaphyseal chondrodysplasias are considered short-limb dwarfing conditions.