Ehlers-Danlos Syndrome.
Last updated Friday, February 18, 2005
Incidence and risk factorsWho gets ehlers-danlos syndrome and why? EDS is a relatively rare disorder, occurring in fewer than 1 in
20,000 people. The various forms of EDS are characterized by
abnormalities in the chemical structure of the body's connective
tissues (for example, skin, muscles, tendons and ligaments). As a
result, skin may become fragile and joints unstable.
What is the role of genetics in acquiring or developing ehlers-danlos syndrome? This section gives a brief description of how EDS is inherited.
Before reading about heredity, understand that parents have no
control over which genes they pass on to their children or receive from
their parents. Therefore, parents should not feel at fault if one or
more of their children inherits EDS.
An inherited disorder is one that is passed on within families from
one generation to the next. It is a result of a change (mutation) in
one of the 50,000 or so genes found on the chromosomes (the thread-like
structures found in the center of each cell). Genes are like blueprints
that direct the development and function of every cell in a person's
body.
Genes and chromosomes exist in pairs. At the time of conception, one
half of each gene pair is passed on to the child from each parent. The
new gene pairs determine which features or traits the child inherits.
Most inherited genes are normal. However, sometimes a gene changes
from its original form. This change is called a "mutation." The exact
reasons why a mutation occurs are usually unknown. Mutations can occur
frequently. Most mutations are not harmful, but occasionally a mutant
gene functions improperly and causes a disorder, malfunction or
malformation. Different mutations of connective tissue genes cause the
distinct forms of EDS.
There are three different ways in which the various types of EDS can
be inherited: autosomal dominant, autosomal recessive and X-linked
recessive inheritance. A family with one type of EDS will not develop
another type, and the inheritance pattern will be the same within a
family.
Autosomal Dominant Inheritance is the way in which the most common
forms of EDS such as Types I and II are inherited. With this type of
inheritance pattern, the EDS gene is dominant. This means it overrides
the effects of the other gene in the pair. Therefore, if a parent who
has EDS contributes the Ehlers-Danlos gene and the other parent
contributes a normal gene, the child will inherit the disorder. This
results in a 50% chance of passing EDS on to each child. On the other
hand, both parents may contribute a normal gene, so there is also a 50%
chance that each child will not have EDS.
Autosomal Recessive Inheritance is the way in which EDS VI, VII and
X are inherited. In recessive inheritance, the disorder is only
inherited if both genes in the gene pair are EDS genes. For a child to
be affected, both parents must pass on an EDS gene. With each
pregnancy, there is a 25% chance that each child will have the
disorder. There is a 50% chance that a child will not be affected, but
will inherit one EDS gene and be a "gene carrier." A carrier is
unaffected, but carries the EDS gene which can be passed on to his or
her children. A carrier could have children affected with EDS only if
the carrier's spouse also carries an EDS gene.
X-Linked Recessive Inheritance is the way in which EDS V is
inherited. With X-linked recessive inheritance, genes are transmitted
on the "X" chromosome which also carries genes that determine the sex
of the child. If a woman carries an EDS gene, there is a 50% chance
that her sons will inherit EDS and a 50% chance that her daughters will
be gene carriers. If a man carries an EDS gene, all of his daughters
would be gene carriers, but none of his sons would be affected and none
would be carriers.
This material may not have answered all of your questions. We
encourage you to discuss your concerns with a genetic counselor or with
a knowledgeable doctor. Contact your local chapter of the March of Dimes for a listing of genetic counseling centers in your area.
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