Finding a gene can be like a treasure hunt.

At first it might seem weird that researchers found a bit of DNA involved in baldness but that they can't figure out why it is involved. The reason for this has to do with the way people find DNA involved in disease.

Human DNA is a long string of 3 billion letters (or bases). Each human is unique because these letters are arranged in a certain order*.

It is too expensive to figure out all of the bases of the DNA from the hundreds or thousands of people involved in a typical study. So what scientists have done is figured out millions of places in human DNA where these letters are often different between people. (This is called the HapMap.)

These differences or SNPs (single nucleotide polymorphisms) work like landmarks to help scientists find which part of the DNA to focus on. They are like clues on a treasure map.

The first part in using a treasure map is narrowing down what part of the world the treasure is in. Imagine the map shows that the treasure is in San Francisco. Then there might be clues that the treasure is near a certain hill or near an oddly shaped tree. Perhaps the treasure is buried near the tower on Mt. Sutro.

With this information, the treasure seekers can get digging. If they know a treasure is in San Francisco, they can't just dig up the whole city. But if they know it is near the tower on Mt. Sutro, then they can dig all over that area.

This is how DNA searches work too. Scientists use SNPs as landmarks to narrow down DNA regions to focus on.

Instead of a treasure map, scientists use the HapMap. They use this map to compare the DNA of people with and without the condition they are interested in. In these studies, scientists compared the DNA of balding and not balding men.

The first study looked at German men. One experiment in this study compared 296 balding men to 347 German men and women who were not seriously bald. The researchers looked at over 500,000 different spots on their DNA and found that bald people shared a number of landmarks in a 1.7 million base chunk of chromosome 20. They had narrowed it down to San Francisco.

More clues led them to a single letter difference that was shared by many of the balding men. A second experiment looked at 319 bald men and compared them to 234 men who weren't bald by the age of 60. This second experiment confirmed the results of the first one.

The second study was done similarly. They compared 578 Swiss men with male pattern baldness to 547 Swiss men who weren't balding. They found a different SNP near the one the first study found. They confirmed that this DNA difference as associated with baldness in over 3000 other individuals from a variety of Northern European countries.

So these two studies have narrowed down where the "treasure" is. They made it to Mt. Sutro. They know that something on a small section of chromosome 20 is partly responsible for balding in Northern European men.

The next steps will be to do some serious digging and to find the treasure. In other words, the researchers need to figure out what in this region is causing these men to bald early. And once they do that, they need to find out why these men go bald. With that information, they might be able to create medicines that can treat baldness.

Usually there is a gene nearby that researchers can investigate. In this case, there isn't. The SNPs are in the middle of nowhere with the nearest gene being at least 350,000 bases away. So researchers have their work cut out for them.

In doing these studies, the researchers also rediscovered the DNA difference that men can inherit from their mom's dad that can lead to early balding.

*The exception is identical twins who have essentially the same DNA but are still unique for environmental reasons.

See original here:
The Genetics of Balding | Understanding Genetics

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