Lavinia Warren, a person with primordial dwarfism - a very rare subtype where an individual is undersized even in utero and may reach an adult height of less than 1 meter. The shortest humans on record were of this sub-type.
Dwarfism refers to a condition of extreme small size of an animal, or plant. Any type of marked human smallness could be termed dwarfism in older popular and medical usage. The term as related to human beings (the major subject of this article) is often used to refer specifically to those forms of extreme shortness characterized by disproportion of body parts, typically due to an inheritable disorder in bone or cartilage development. There are about 200 different types of dwarfism, each linked to a specific genetic condition and a particular set of growth patterns.
Forms of extreme shortness characterized by proportional body parts usually (but not always) have a hormonal or nutritional cause. An example is growth hormone deficiency, once known as "pituitary dwarfism". However, some rare types of genetic dwarfism, such as Primordial dwarfism, also exhibit with correct proportions compared to an average person.
The Little People of America (LPA) defines dwarfism as a medical or genetic condition that usually results in an adult height of 4'10" (147 cm) or shorter.
The form of dwarfism that is portrayed in Merry Little Christmas is Cartilage-hair hypoplasia. This is the form of dwarfism exhibited by Billy Barty and Verne Troyer.