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| X ray showing the skull and spine of a person with achondroplasia |
Achondroplasia
Definition
Achondroplasia, or short-limb dwarfism, is the most common form of
abnormally short stature in adults. It is caused by a mutation in a single gene
on chromosome 4 that regulates the conversion of cartilage to bone. This
gene is the only gene that is known to be associated with achondroplasia.
Description
Achondroplasia is basically a disorder of bone development. The skeleton
of a human fetus is composed primarily of cartilage, a dense and somewhat
elastic form of connective tissue that gradually turns to bone during
normal development. In a person with achondroplasia, a gene that is
involved in the process of bone formation produces too much of a protein
that limits bone growth. As a result, the person with achondroplasia has
unusually short bones in the arms and legs and other skeletal abnormalities.
They also usually have difficulties with posture, joint disorders, and
breathing problems in later life.