A Breakthrough Global Study of Depression Finds 44 Genetic Variants Linked to the Disease

iStock
iStock

Though depression affects an estimated 14 percent of the world’s population, scientists know very little about the underlying causes of the disorder, and that makes it incredibly difficult to treat. Even now, researchers are still debating whether common antidepressant medications even work at all, and if they do, why.

New research published in the journal Nature Genetics provides a big step in figuring out why some people suffer from depression while others don’t, identifying 44 genetic variants that are risk factors for major depression, 30 of which are new. They also found two regions of the brain that appear to be associated with the development of the disorder.

The study is the result of an international effort by more than 200 researchers involved with the Psychiatric Genomics Consortium. It looked at more than 135,000 cases of depression (both self-reported and clinically assessed) and almost 345,000 control cases. It’s the largest study on the genetic basis of depression ever done.

The researchers found that all humans carry some of the 44 risk factors identified. Some people carry more than others, putting them at greater risk for developing depression. They also identified the prefrontal and anterior cingulate cortices (both located at the front of the brain) as the regions of the brain probably linked with the development of depression.

Some of the risk factors the researchers identified are also involved in other psychiatric disorders, like schizophrenia, which isn't entirely surprising—a 2007 study from the Psychiatric Genomics Consortium found that people with depression, bipolar disorder, and schizophrenia as well as developmental disorders like ADHD and autism share the same variations in four locations in their genetic code.

By identifying genetic risk factors associated with major depressive disorder, the scientists hope to increase our understanding of why depression strikes some people and not others. "[M]ajor depression is a brain disorder," the researchers conclude. "Although this is not unexpected, some past models of [major depressive disorder] have had little or no place for heredity or biology." They firmly put to rest the idea that depression is entirely a matter of environment.

Environment certainly plays a role—the researchers found links between lower education levels and higher body mass index and depression risk as well—but genetics may impact whether someone whose circumstances put them at risk of depression actually develops the disorder. Depression is still highly stigmatized, which often prevents people from seeking treatment for it, according to several studies. Further understanding of the genetic underpinnings of the disorder may help counter negative perceptions of depression as a character flaw or a sign of laziness.

The study could eventually change how doctors treat depression. Many of the genetic variants identified by this study are linked to targets of current antidepressant medications, like serotonin. But the research may also lead to the development of new medications and therapies that could work for more people (current medications don't work for everyone) and potentially have fewer side effects than existing treatments.

The study partially relied on self-reported depression diagnoses, meaning there's some wiggle room in knowing whether those people are actually clinically depressed to the degree that a medical professional would diagnose. Further research will need to confirm that these genetic variants are indeed linked to depression. There are likely even more gene variants related to depression risk, as well, but they might have too small of an effect to be identified by this study. The researchers hope to continue their work to understand the links between environmental stressors, genetic variations, and depression risk in the future.

Whiten Your Teeth From Home for $40 With This Motorized Toothbrush

AquaSonic
AquaSonic

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7 Facts About the Hurricane Highway

Hurricane Earl (top) and Hurricane Fiona (bottom) pummel the U.S. coast and Caribbean islands.
Hurricane Earl (top) and Hurricane Fiona (bottom) pummel the U.S. coast and Caribbean islands.
NOAA/NASA GOES Project // Public Domain

Autumn is the peak of hurricane season, also known as Cape Verde season, after the islands where the so-called "hurricane highway" originates. Here are seven facts about this awesome—and sometimes deadly—weather phenomenon.

1. The hurricane highway begins near the African coast.

The Cape Verde Islands, located off the northwest coast of Africa, are where the hurricane highway starts. Thunderstorms destined to become hurricanes often form into a tropical depression near the islands, slowly organizing and strengthening over the following week as the system moves toward the Caribbean. These storms have a long time to get their act together, but they also have to cover a lot of distance without losing their power to reach the East Coast as a hurricane. Some storms are able to thrive with little wind shear, ample warm water, and moist air, while others starve and dissipate if they encounter cooler waters and strong winds, or ingest dry, dusty air blowing off the Sahara Desert.

2. An easterly jet stream gives rise to the hurricane highway.

It’s hard to imagine from North America that a couple of thunderstorms on another continent thousands of miles away can swirl up into a monstrous storm, but it happens almost every year. The extreme temperature gradient between the blistering heat of the Sahara Desert and the more temperate climate of the savanna to its south creates an easterly jet stream that triggers clusters of showers and thunderstorms. These clouds then move from east to west, emerging off the western African coast near the Cape Verde Islands. Every year, the right conditions turn a handful of these localized storms into tropical storms that make their way across the Atlantic.

3. The biggest hurricanes start with the smallest storms on the hurricane highway.

Hurricane Andrew was a Category 5 hurricane when it made landfall in Homestead, Florida.Xanxz/NOAA, Wikimedia Commons // Public Domain

Hurricanes, cyclones, typhoons—these are all names for the same force of nature, like Hurricane Andrew, which hit the East Coast in 1992. Cyclones like Andrew don’t just form out of thin air. All tropical cyclones require a relatively tiny “nucleus” of thunderstorms in order to develop. When the air and water temperatures are right, these groups of thunderstorms sometimes spin up into a fierce low-pressure system capable of causing a lot of damage. We see lots of these seedling thunderstorms over the ocean every year, but only a small number of them become hurricanes.

4. Hurricanes form in different places in different months.

Where a tropical storm or hurricane begins its trip across the ocean depends on what time of the year it forms. Storms that form early in the season usually get their start from thunderstorms or cold fronts that stall over the water very close to land; almost all of the storms that form in the Atlantic in June come to life within a few hundred miles of land. When we reach the peak of hurricane season, though, they start to form farther and farther out in the ocean—all the way out to the shores of Africa.

5. Fall is the peak of hurricane season on the hurricane highway.

Hurricane season in the Atlantic Ocean runs from June 1 through November 30. Storms are most common during that six-month stretch of the year, but sometimes they can form earlier or later too. That said, the period between the middle of August and the middle of October is typically the climatological peak of the season. That’s because, as the ocean water gets warmer, the atmosphere becomes conducive to vigorous storms, increasing the risk for hurricanes and tropical storms.

6. Cape Verde hurricanes can easily land in the record books.

This image shows the tracks of all tropical cyclones recorded in the Atlantic Ocean between 1851 and 2014.
Dennis Mersereau

Tropical waves traveling west from the coast of Africa in the middle of the summer are the culprits behind some of the worst hurricanes we’ve experienced in the United States. For example, on August 8, 2005, a small tropical wave emerged off the coast of Africa, soon becoming Tropical Depression 10. That depression would fall apart a few days later, but its remnants kept moving toward the U.S., redeveloping into a new tropical depression over the Bahamas on August 23. That new tropical depression became Hurricane Katrina, the costliest hurricane to ever strike the United States.

It’s a similar story for many—but not all—major hurricanes in recent history. Hurricanes Andrew, Dennis, Ivan, Isabel, and Ike were all Cape Verde–type storms that sprang to life thousands of miles away from where they would ultimately wreak havoc.

7. Strong hurricanes can still form in other places in autumn.

While the far eastern part of the Atlantic Ocean is a hotbed of activity this time of the year, it’s not the only place you need to watch if you live near the coast. Storms that form close to land can quickly spin themselves into catastrophe. Hurricane Sandy formed just south of Jamaica and hit New Jersey in a matter of days in 2012. A tropical depression that developed east of Florida on September 18, 2005, exploded into Hurricane Rita just three days later, with 180 mph winds—the most intense storm ever recorded in the Gulf of Mexico.

Meteorologists are currently predicting an above-average hurricane season in 2020. It may be worth preparing: NOAA suggests gathering a few key disaster supplies to have on hand, getting an insurance check-up, and locating the safest high ground.