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Periventricular Heterotopia
You’ve been told that you or your child has a condition called
periventricular heterotopia (PH). Most people have never heard of this and
have no idea what it means for themselves, their child, or their family.
This information sheet gives you some general information about PH. Our
knowledge of PH is expanding all the time but we still have many unanswered
questions about this disorder.
What is periventricular heterotopia?
Periventricular heterotopia (PH) is a term that refers to a particular
abnormality in the way that the brain developed during pregnancy. During
normal brain development, neurons (brain cells) develop near the ventricles,
which are fluid-filled spaces deep in the brain. These cells then migrate
outward from the ventricles toward the surface of the brain and eventually
become the gray matter at the brain surface, which is called the cerebral
cortex. In PH, there are nodules or clusters of brain cells that remain near
the ventricles (“periventricular” means near the ventricles and
“heterotopia” means misplaced). Our current understanding is that these
neurons failed to properly migrate outward to the brain surface as they were
supposed to.
PH usually occurs by itself, although it can sometimes be seen in
association with other abnormalities of brain development, like
polymicrogyria. PH can range in severity from just a single nodule of
neurons near the ventricle on one side of the brain, to multiple nodules
that fuse with each other and are present along the entire extent of the
ventricles on both sides of the brain.
How is periventricular heterotopia diagnosed?
MRI (magnetic resonance imaging) is the best way to diagnose periventricular
heterotopia (PH). Sometimes, CAT (computed axial tomography) scans might
show signs that suggest that PH could be present, but MRI is the most
definitive method.
How will periventricular heterotopia affect me or my child?
Many patients with periventricular heterotopia (PH) have a seizure disorder,
or epilepsy. The seizures most commonly begin in the teenage years, and are
treated using the same anti-seizure medications used to treat seizures of
any cause. Although PH is present in the brain from birth, it is often first
diagnosed when a neurologist orders an MRI after the individual begins
having seizures. We do not know why seizures do not usually appear earlier
in life.
Most individuals with PH have no other neurological problems other than
seizures – they have normal intelligence, perform well in school, and
function completely normally. However, recent research in our lab has shown
that even patients with generally normal function may actually have some
specific learning disabilities related to their PH of which they may not be
aware. Some patients with PH do have slight degrees of mental retardation.
It also appears that some patients with PH can have other problems outside
of the brain, such as in the heart or blood vessels. We are currently doing
research to investigate what types of problems are included and how often
they occur.
What causes periventricular heterotopia?
Periventricular heterotopia (PH) can arise from multiple different causes.
Although it is possible for problems during pregnancy, such as infections or
lack of oxygen to the fetus, to cause PH, usually the cause is a genetic
problem (i.e., a change in the DNA). Genetic problems include both those
that run in families and those that have appeared for the first time in the
person who is affected. Research in our lab has shown that changes in a
particular gene called filamin A are responsible for many cases of PH. The
filamin A gene is responsible for making a protein that is required for
brain cells to migrate properly. However, we have also identified changes in
other genetic regions that can cause PH in certain people. It is important
to distinguish between these genetic possibilities because they determine
how likely a subsequent child might be affected by the same disorder.
Am I appropriate for your research studies?
There are currently two parts to our periventricular heterotopia (PH)
research. First, we are continuing to look for potential genes that may be
involved in this disorder, besides the ones we have already discovered. This
work involves collecting blood samples from affected patients and their
family members so that we can look for potential gene changes that may be
linked to this disorder.
The second part of our research focuses on how individuals are actually
affected by PH. In this study, we are using cognitive testing, brain MRI
scanning, and other methods to look for learning disabilities and to
evaluate how brain function is affected by the presence of the misplaced
nodules of neurons in this disorder. We are also doing special studies to
look at the heart and blood vessels to determine whether abnormalities are
present there as well.
If you are interested in this study, please contact our research coordinator by e-mail at
walshlab@bidmc.harvard.edu
or by phone at (617) 667-8035.
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Christopher A. Walsh
Laboratory