What Causes Hereditary Angioedema?
Researchers are still trying to determine the exact cause of hereditary angioedema (HAE),
but much is known about the role played by
complement 1 esterase inhibitor, or C1-INH. A defect in a person’s genetic
code for the C1-INH protein may be responsible for HAE. An abnormal code can lead
to a deficiency in C1-INH (type I HAE) or an inability of existing C1-INH to function
properly (type II HAE).
In order to understand how HAE is inherited, it’s helpful to look at genetics. People
receive half their genetic code from their mother and half from their father. In
some diseases, such as cystic fibrosis or sickle-cell anemia, a child must receive
the abnormal, disease-causing gene from both parents. Biologists call these
autosomal recessive genes. The parents of the affected child have the
gene, but may not have the disease — these parents are considered carriers of the
disease.
This is not the case in HAE. In HAE, just one defective gene will cause the disease.
Biologists call this anautosomal dominant gene. This means that there is a 50-50 chance that
a child who has one parent with HAE will also have HAE.
Children born without the abnormal gene will effectively prune the occurrence of
HAE from that branch of the family tree. All successive generations (that child’s
children and grandchildren) will be free of HAE.
Rarely, HAE can occur in a person without a previous family history of HAE. This
is due to a spontaneous change in the genetic code for the C1-INH protein. Not only
will this person have the disease, but he or she will also have the potential to
pass this changed gene (and the disease) to his or her children.