Dwarfism can be caused by more than 200 different medical conditions. The most common cause of dwarfism is achondroplasia, a bone growth disorder responsible for 70% of dwarfism cases. Conditions in humans characterized by disproportional body parts are typically caused by one or more genetic disorders in bone or cartilage development. Forms of extreme shortness in humans characterized by proportional body parts usually have a hormonal or nutritional cause such as growth hormone deficiency, once known as "pituitary dwarfism"
The most recognizable and most common form of dwarfism is achondroplasia, which accounts for 70% of dwarfism cases and produces rhizomelic short limbs, increased spinal curvature, and distortion of skull growth.
Achondroplasia is a result of an autosomal dominant mutation in the fibroblast growth factor receptor gene 3 (FGFR3), which causes an abnormality of cartilage formation. FGFR3 normally has a negative regulatory effect on bone growth. In achondroplasia, the mutated form of the receptor is constitutively active and this leads to severely shortened bones.
(Source: Wikepedia- various)