Ask a Geneticist

by Gwen Liu, Stanford University

Is the skin disease vitiligo genetic? Will it transfer to my kids?

-A graduate student from California

July 15, 2010

A famous case
of vitiligo.
Vitiligo is a disease where patches of skin become discolored. About 30% of people with vitiligo also have a family member with it. This means genetics almost certainly has something to do with it. But for reasons I’ll get to in a second, there are probably other factors involved too.

On average 1 in every 100 people have vitiligo. Your chances increase to 1 in 20 if a parent or sibling has it. If we go by these statistics, then there is a 5% chance you will transfer vitiligo to your kids.

Remember though that these are just statistics. We can’t accurately predict what might happen in your specific situation because vitiligo is pretty complicated. Every case is going to be a bit different.

Like I said before, genes are most likely involved. But they’re not the only cause of vitiligo.

We know this from studying identical twins. Identical twins have the same set of genes. So if a disease were solely due to genes, then both identical twins in a pair would always have it.

This is not the case in vitiligo. If one identical twin has it, the other one has it only 23% of the time. This is still higher than in sibling pairs, where 6% of the time both have it. So genetics is involved but something else must be a factor too. Probably something from the environment.

Scientists are working hard to figure out which genes are involved and how other factors might act as a trigger. Before we discuss this, let’s first see what happens in the body during vitiligo. Then we can better understand how genes are involved in the process.

Immune Cells Gone Wild Causes Vitiligo

You get your skin color because of a pigment called melanin. This pigment is made in certain cells called melanocytes.

People with vitiligo have white patches on their skin because their immune system has killed the melanocytes there. No melanocytes, no melanin, white skin.

These white patches happen
when the immune system
kills the cells that
make pigment.
Usually our immune system protects us from infections. It fights off things that are foreign to us like bacteria or viruses.

But sometimes the immune system gets confused and mistakes things from ourselves as foreign. It then goes on to attack and destroy those parts of us. This is called autoimmunity.

Vitiligo is an autoimmune disease. The immune system mistakenly recognizes something about melanocytes as foreign and destroys them.

People with vitiligo often have very confused immune systems. These folks sometimes will have other autoimmune diseases like lupus, hypothyroidism, or inflammatory bowel disease. This is probably because genes of the immune system play a role in all these diseases.

Genes and Vitilgo

Just to review, genes are the instructions for life that make and run us. Generally one gene has the instructions to make one protein. And each protein does a specific job in the body.

So we have a gene that makes insulin that helps us use sugar. And one for hemoglobin that helps our bodies carry oxygen in the blood. And so on.

Scientists compared the genomes (entire set of genes) of groups of people with and without vitiligo. They found more than 10 genes associated with vitiligo. As we might have guessed, some of these genes are involved in the immune system. And some with melanocytes.

It is important to mention that people with vitiligo don’t have genes that other people don’t have. There is no vitiligo gene. These folks just have different versions of these 10 genes that we all share.

Different versions mean different instructions. Which means a slightly different protein may get made.

These slightly different proteins may look or act differently than the ones made by people without vitiligo. And something about these differences causes the destruction of melanocytes.

Let’s discuss two of the identified genes and see how they might cause vitiligo. These two give a nice overview of how the immune system can get confused.

People with autoimmune
diseases have immune
systems that see red
flags on their own cells.
MHC. The MHC (major histocompatibility) genes play an important role in the immune system. They label cells so the immune system can either pass by or attack.

For example, when bacteria infect a cell, MHC can display bits of bacterial proteins on the outside of the cell. Sort of like a red flag. When the immune system sees this, it attacks any cell that has the red flag. This includes the bacteria.

People with vitiligo have a different version of one of these MHC genes. The idea is that this MHC sees something about a melanocyte as a red flag. This makes the immune system think that the melanocyte is an invader.

So the immune system attacks and destroys the melanocytes. The end result is vitiligo.

TYR. The TYR gene makes a protein called TYR. This protein helps make the pigment melanin in melanocytes.

People with vitiligo have a different version of the TYR gene. What scientists think is happening is that the immune system attacks the melanocytes because this TYR protein looks suspiciously like a red flag. A case of mistaken identity that leads to the destruction of melanocytes which leads to vitiligo.

So things can go wrong on either end. Sometimes a gene in an immune cell makes it attack the melanocyte. And sometimes a gene in the melanocyte makes the immune system attack it.

Many of the other genes that scientists found act similarly. Some work in the immune system and others in melanocytes.

They also found other genes that weren’t so easy to explain. Once they figure those out, scientists will learn a lot about vitiligo. And a lot about melanocytes and the immune system.

Treatments and Future Therapies

You can probably tell that there are a lot of genes to sort through to get to the bottom of vitiligo. Most likely a combination of these genes along with other triggers are responsible. Some of these triggers might be stress, sunburn, or exposure to certain chemicals.

Even though vitiligo is not life threatening, it can be emotionally and psychologically difficult to deal with. There are several treatments currently available. Topical creams weaken the immune system to slow melanocyte destruction. UV light therapy can repigment the discolored patches. Bleaching the surrounding skin can even out skin tone. (This is the treatment Michael Jackson opted for.)

Different things in different people probably cause vitiligo. The recent discovery of several associated genes may lead to new and promising therapies. By looking at a patient’s genes, doctors may personalize an effective treatment for each individual.

Gwen Liu

Ask a Geneticist

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