Skeletal dysplasia is caused by a genetic mutation. The gene mutation can occur spontaneously or can be inherited.
Diastrophic dysplasia and usually spondyloepiphyseal dysplasias are inherited in a recessive manner. This means a child must receive two copies of the mutated gene -- one from the mother, one from the father -- to be affected.
Achondroplasia, on the other hand, is inherited in a dominant manner. That means a child needs only one copy of the mutated gene to have that form of skeletal dysplasia. There is a 25% chance that a child born to a couple in which both members have achondroplasia will be of normal height. But there is also a 25% chance the child will inherit both dwarfism genes, a condition known as double-dominant syndrome. This is a fatal condition that usually results in miscarriage.
Often parents of children with achondroplasia do not carry the mutated gene themselves. The mutation in the child occurs spontaneously at the time of conception.
Doctors do not know what causes a gene to mutate. It is a seemingly random occurrence that can happen in any pregnancy. When average-size parents have a child with dwarfism due to a spontaneous mutation, it is not likely that other children will also have the mutation.
In addition to genetic skeletal dysplasia, short stature has other causes, including disorders of the pituitary, which influence growth and metabolism; kidney disease; and problems that affect the body's ability to absorb nutrients.
Some forms of dwarfism are evident at birth or during infancy and can be diagnosed through X-rays and a physical exam. A diagnosis of achondroplasia, diastrophic dysplasia, or spondyloepiphyseal dysplasia can be confirmed through genetic testing. In some cases, prenatal testing is done if there is concern for specific conditions.
Sometimes dwarfism doesn't become evident until later in a child's life, when dwarfism signs lead parents to seek a diagnosis. Here are signs and symptoms to look for in children that indicate a potential for dwarfism: