生物が非常に小さいとき小人症が発生します。
Dwarfism, also known as short stature, occurs when an organism is extremely small. In humans, it is sometimes defined as an adult height of less than 4 feet 10 inches (58 in; 147 cm), regardless of sex, although some individuals with dwarfism are slightly taller. Disproportionate dwarfism is characterized by either short limbs or a short torso. In cases of proportionate dwarfism, both the limbs and torso are unusually small. Normal intelligence and lifespan are usual. Treatment depends on the underlying cause. Those with bone growth disorders can sometimes be treated with surgery, or physical therapy. Hormone disorders can be treated with hormone replacement therapy as well before the child's growth plates fuse. Individual accommodations, such as specialized furniture, are often used by people with dwarfism. Many support groups provide services to aid individuals and the discrimination they may face.