Indications for PGD
Family history of X-linked disease
A category of monogenic diseases has an X-linked
inheritance. Most couples at risk for an X-linked condition
are identified by review of the family history or the birth
of an affected child. X-linked conditions are caused by a
change, or mutation, in a gene on the X chromosome and
typically affect only males.
This is because males have only one X chromosome, inherited
from their mother, while they get a Y chromosome from their
father. Since a male has only one X chromosome, if it has a
mutated gene he will develop the disorder. It is this type
of inheritance that causes disorders such as Duchenne
Muscular Dystrophy, Hemophilia, Fragile X, etc.
Females are usually not affected because they have two X
chromosomes. Females with one normal X chromosome and one
mutated X chromosome generally do not have symptoms of the
disease because of the presence of the normal gene.
These females are referred to as ?carriers? and are at risk
for passing on the gene mutation to their children. If that
child is a girl who inherits the gene, she also will be a
carrier. Once the sex of the embryo is determined, female
embryos, which would not be at risk for a sex-linked
disorder, would be transferred.
Inherited genetic disorders