Joshua Lorenz, age 14, of Baltimore, Md., for his question:
WHAT CAUSES DWARFISM IN SOME HUMANS?
A human dwarf is a very small person who grows no more than four and a half feet tall as an adult. Human dwarfism occurs as the result of an underdeveloped skeleton. The growth of the skeleton depends on the formation of tissue called cartilage. Dwarfism results when the cartilage cells do not grow and divide properly.
Such improper development of cartilage cells may occur because of defective cells or interference with the growth of otherwise normal cartilage cells. Defective cartilage cells cause chondrodystrophic dwarfism or chromosome related dwarfism, depending on whether the cell defect is restricted to the cartilage cells alone or is part of a more widespread cellular disorder.
The interference with the growth of normal cartilage cells results in hormonal dwarfism or nonhormonal dwarfism, depending on what causes the interference.
Chondroystrophic dwarfism occurs when only certain cartilage cells are defective. Chondrodystrophic means "underdeveloped cartilage." The defective cells occur only in the spine or only in the arms and legs. Consequently, either the torso (chest, abdomen and hips) or the limbs grow unusually short.
Chromosome related dwarfism results when all the cells of the body, including the cartilage cells, are defective.
Hormonal dwarfism may occur when a hormone deficiency interferes with the growth of normal cartilage cells. An insufficient amount of a growth producing hormone leads to stunted growth.
As an example, a shortage of growth hormone results in a dwarf with normal proportions. Insufficient insulin leads to the disease diabetes mellitus and a shortage from birth of thyroxine causes cretinism. Both these disorders interfere with growth and may lead to dwarfism.
Nonhormonal dwarfism occurs if disease or improper nourishment blocks the growth of cartilage cells.
The hormones that stimulate growth include growth hormone from the pituitary gland, insulin from the pancreas and thyroxine from the thyroid gland.
Children who lack a certain growth promoting hormone may be treated by physicians. Since the mid 1960s, doctors have given growth hormones to children who lack this hormone. But only limited amounts of growth hormone are available and many youngsters remain untreated. Insulin and thyroxine, which are readily available, may be given to stimulate growth in children affected by diabetes or cretinism.
Dwarfism occurs both in individual organisms and in entire groups of organisms. Such groups include African Pygmies, Shetland ponies and the various kinds of dwarf trees.
There are several kinds of normal dwarf animals, including dwarf cattle and toy dogs. Dwarf plants include ornamental fruit trees and several varieties of flowers, such as marigolds and dahlias.