Genetic Counseling and VCFS: A Basic Review
Deborah Hung Copenheaver, M.S.
Children’s National Medical Center, Washington, D.C.
VCFS is a genetic disorder associated with
a deletion of chromosome #22q11. Chromosomes are found in the cells of the human
body and contain genes (or genetic information). This genetic information
controls how a person looks and how the body develops and functions. Usually,
there are 46 individual chromosomes arranged in 23 pairs and they are found in
the cells of the body. Each parent contributes one chromosome to each pair.
There are 22 autosomal pairs of
chromosomes and one sex-determining pair. Each chromosome can be divided in to
two halves. The short half is called the p-arm while the long half is called the
q-arm. The deletion that causes VCFS is found on the q-arm of chromosome #22.
VCFS is an autosomal dominant disorder. Autosomal refers to the fact that the
deletion is not found on the sex chromosomes and both males and females can be
affected. Dominant means that only one of the chromosomes in the #22 pair needs
to be affected in order to have the disorder.
In ~85-90% of cases of VCFS, the child is the first person in the family to have
the disorder and there is no family history of the disorder. The mechanism of
how and why a deletion occurs is not fully understood, but we do know that there
is nothing that a parent does before or during a pregnancy that causes a
deletion to occur. In the other ~10-15% of cases, one of the parents has VCFS
and has passed it on to their child. Because the physical finding associated
with VCFS can be subtle and vary from person to person, even within a family,
often a parent does not know they have VCFS until their child is diagnosed.
When a person has the deletion in one of their #22 chromosomes, there is a 50%
or 1/2 chance that they will pass on that chromosome to their offspring. There
is also a 50% or 1/2 chance that they will pass on the non-deleted chromosome
and their offspring will not have VCFS. Prenatal diagnosis is available to
determine if a pregnancy is affected.
If your child has VCFS and you need
help explaining inheritance or the diagnosis to them, your local genetic
counselor may be able to help you.