Dictionary of Human Evolution and Biology

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Dwarfism, Pituitary

Condition of being significantly smaller than average, especially when accompanied by disproportionate growth, and usually caused by low levels of human growth hormone. Aka pituitary dwarfism. There are four modalities of genetic hypopituitary dwarfism, all autosomal recessive; in each case growth dysfunction begins prenatally. Type I is primordial dwarfism, in which only growth hormone (GH) is deficient, and the result is a midget of normal proportions; nanism. Type II is ateliosis due to hGH-receptor deficiency; this type cannot be treated with exogenous GH. Aka Laron type dwarfism, GH insensitivity. Type III is the panhypopituitarism type of dwarfism, in which all hormones of the anterior pituitary gland are deficient. Type IV is Kowarski syndrome dwarfism, in which the receptor is present but GH concentrations are low; unlike type II, exogenous GH induces a significant increase in growth rate. The genetic forms are as a group less common than hypopituitarism caused by a tumor or secondary to an infection.

Cf. achondroplasia and nanism.

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