STEP Study Snippets: Sturge-Weber Syndrome

This little guy is showing the classic "port-wine" stains associated with Sturge-Weber

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I'm about to embark on a couple months of intensive studying for the first major standardized test I'll need to take on my path to becoming a doctor: the USMLE Step 1 exam. I figured I'd just write some short posts about some interesting pathologies/medical facts that I learn along the way. Feel free to ask any questions you might have in the comments!

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What is it?

Sturge-Weber Syndrome is a congenital malformation of blood vessels around certain nervous system tissues.

How does it happen?

Part of the interesting aspects of Sturge-Weber is the fact that it is a mosaic mutation of a specific gene called GNAQ. Mosaic mutations occur in one of several cell lines that exist in a fetus after a number of cell divisions and not on the chromosomes of the embryo right away.

What this means is that only a certain, minor portion of the cells in a Sturge-Weber patient's body are affected by the mutation as opposed to all of the cells, like most other diseases that arise from mutations. The fact that Sturge-Weber is a mosaic mutation is important because the mutation is very serious, and embryos/fetuses can only survive if the mutation is limited to a small fraction of their body.

GNAQ, the gene that is mutated in this disease, is an important regulator of blood vessel formation in a growing/developing fetus. In short, a mutation to this gene (such as the mutation in Sturge-Weber) can lead to extra blood vessels existing in a person's body where they shouldn't be, and this can lead to problems.

What does it cause?

As mentioned above, mutations to GNAQ can cause issues with blood vessel formation. GNAQ specifically governs the regression of extra blood vessels that exist during an embryo's development, but are normally not needed after the child reaches a certain age.

Typically, there is a specific group of blood vessels that surround the trigeminal nerve (the fifth cranial nerve) of the face that exists for a few weeks in an embryo before being replaced by other blood vessels. In a Sturge-Weber patient, this plexus (or group) of blood vessels does not disappear, and therefore there are extra blood vessels in the face. This excess of blood vessels leads to the classic red "stain" on the patient's face from the day they are born.

Here's a picture of what that looks like.

This red "stain" blanches (turns white when you press on it with a finger for a bit), but otherwise stays on the patient's face.

There are more serious conditions/symptoms that can be associated with Sturge-Weber, most of which are caused by the extra blood vessels taking up too much space in the patient's face/head. Some of these complications include: Strokes, seizures, and glaucomas. These are serious symptoms, so it's important to be aware if you or someone else has this syndrome!

How do we diagnose it?

Diagnosis of Sturge-Weber is done by genetically testing affected tissues on the face (because other parts of the body won't have the mutations). Patients with Sturge-Weber have pretty recognizable facial features (the "stain"), but its important to make sure the GNAQ mutation is really what is causing the issue.

Is it contagious?

Not at all, and because it is mosaic it cannot even be passed down from parents to their children.

Can it be treated?

The most important aspect of treatment for Sturge-Weber is preventing the bad complications (stroke, etc.) from happening in the patient. Generally, doctors will image the inside of the patient's head to make sure there aren't any vascular problems directly affecting the brain itself as well as doing regular eye exams and EEGs to test for seizures and glaucomas.

The good news is that we know enough about Sturge-Weber to start these preventative measures immediately, and the outcomes for these patients have drastically improved in the recent years!

Thanks for reading! Feel free to ask any questions in the comments!