The ABC(C)s of Sleep

A Small Difference in the ABCC9 Gene Might Cause People to Need Less Sleep
Do you ever wish you were one of those people who need less than 8 hours every night? Or have you ever wondered why you are one of these lucky people? You might be surprised to learn that your genes have something to do with how much sleep you need. Of course genes can't explain everything about sleep. Other factors like age, gender and time of year can affect how many hours of sleep you need. And your health can play a big role, too.

Your genes might have
something to do with
how much sleep you need.
Pregnant women often have trouble sleeping well at night. And lots of diseases can cause sleep problems, too. Some of these diseases are even genetic and so can run in families. But until recently, it hasn't really been clear why some healthy people just need less sleep at night. A few studies have shown that small differences or variations in these people's DNA might play a role. Most of these differences are in genes that control circadian rhythm, also known as our body clock. A new study found a different sort of gene though. It found that people with a certain difference in a gene called ABCC9 needed about half an hour less of sleep every night. This kind of finding could help people suffering from sleeping problems if scientists find a medicine that does the same thing to their ABCC9 gene. And it might even help to create a safe way for everyone to get away with a little less sleep each night. Sign me up!
Comparing DNA
We're all different people and that has a lot to do with our DNA being different. These differences, called single nucleotide polymorphisms (SNPs), are usually pretty small. Any two unrelated people have about 6 million different SNPs. A lot of times, SNPs can cause certain people to have certain traits. To look for this, scientists use genome-wide association studies (GWAS). In these, they compare the DNA from lots of people and look for people who share both a SNP and a trait in common. So for this study, the researchers first looked at the sleep patterns of more than 4000 people and figured out how much sleep they need each night. They were careful to consider how long people sleep on workdays (when they have to get up at a certain time) and free days (when they can sleep as long as they need). Then the researchers compared all of these people's DNA. They looked for any SNPs that were common in people who needed less sleep and weren't found in people who needed more sleep. They found that people who shared a certain SNP in their ABCC9 gene only slept for 7.5 hours each night, almost a half an hour or 5% less than others. This ABCC9 gene SNP is found in about 1 in 7 people.

Fruit flies are powerful tools
that scientists use a lot
in genetic experiments.
Of course, just because they all share this SNP does not necessarily mean that it causes them to need less sleep. Scientists need more evidence than that. This is why the researchers in this study did an experiment where they "knocked down" or turned down the ABCC9 gene in fruit flies. Fruit flies are a really valuable tool that scientists use all the time in genetic experiments. It's relatively easy to add, change or remove their genes, and most of their genes are related to ours. So we can actually learn a lot about ourselves from studying fruit fly genes. But of course we need to be careful that we don't over interpret the results. Flies and humans are still pretty different from each other, so scientists have to be really careful about any conclusions they make from these kinds of studies. Flies have two sleep periods every 24 hours, one during the day and one during the night. When their ABCC9 gene (called dSur in flies) was turned down, the night sleep period was delayed by almost 3 hours, but the day sleep period was not affected. What does this mean? It suggests that the ABCC9/dSur gene is involved in controlling nighttime sleep duration, but doesn't cause major changes to circadian rhythm, at least in flies. So it's possible that the SNP that the scientists found in the ABCC9 gene causes people to sleep less every night. But before we go making any major conclusions, we need to remember two things. (1) Even though flies and humans have related genes, they are still pretty different from each other. And (2) having a small DNA difference in your ABCC9 gene is probably very different from turning down the dSur gene in flies.

More Information

Potassium and Sleep
Genes contain the information that our cells need to make proteins. And proteins carry out all of the basic functions that we need to stay alive and well.

The SUR2/ABCC9 gene helps
move potassium (K+) ions
in and out of cells.
The ABCC9 gene has the information needed to make a protein called SUR2. The SUR2 protein's job is to help move potassium in and out of cells.* So the next mystery to solve is to figure out what potassium has to do with sleep. Why would a small DNA difference in the ABCC9 gene, which may or may not affect how well the ABCC9 gene is working, control how much sleep someone needs? One clue is that moving potassium ions into and out of cells is really important for our bodies to work properly. It helps to control our heartbeat, metabolism and blood sugar levels. The relationship found in this study between the ABCC9 gene SNP and amount of sleep suggests that potassium may also help control sleepiness. This actually isn't an entirely new idea. Some other potassium channel proteins in the brain have already been reported to control how awake we feel. So what next? If scientists could figure out exactly how this ABCC9 gene SNP causes people to need less sleep, we might be able to figure out ways to help people who have sleep problems. If it really comes down to how much potassium moves in and out of cells, scientists could develop drugs that control this. That way, we might be able to help people get the right amount of sleep they need every night. * The SUR2 protein is officially known as an ATP-sensitive potassium channel subunit. Dr. Maggie Pearce