[ Biology / Medical ] - "The Upside of Bad Genes" by Moises
Velasquez-Manoff
https://www.nytimes.com/2017/06/17/opinion/sunday/crispr-upside-of-bad-genes.html
Sickle cell was a case in point. The gene is usually found in
people who live in, or whose ancestors came from, sub-Saharan
Africa, the Arab world and India; in those places, having one copy
of the gene can prevent the worst symptoms of malaria. Of every
four children our imaginary couple might have, one will probably be
afflicted with sickle cell disease, but two would most likely be
protected from malarial disease.
Ditto with the gene variants that cause the lung disease
cystic fibrosis. In parts of northwest Europe, about 1 in 25 people
carries a single copy of the gene. And while two copies cause
disease, it has long been hypothesized that having just one
protects against tuberculosis — the White Plague that ravaged
Europe for a few hundred years.
Carriers of the ApoE4 variant have an up-to-fourfold
increased risk of Alzheimer’s disease. In 2010, scientists at
Northwestern University found that the gene was more prevalent in
tropical and polar populations than in those from mid-latitudes,
presumably because it served some function in those regions. Then,
strangely, the gene was linked to enhanced cognitive performance in
children living in Brazilian slums. And last year, Ben Trumble, an
anthropologist at Arizona State University, and colleagues
published an intriguing study suggesting that the gene might
improve brain function in elderly people living in the Bolivian
Amazon. The tribe he studied, called the Tsimane, subsist mostly on
what they grow and hunt in the jungle, and about two-thirds have
intestinal parasites. Dr. Trumble discovered that if elderly ApoE4
carriers harbored parasites, their cognitive abilities improved
relative to noncarriers with parasites. Only carriers without
parasites suffered cognitively.
Scientists at Albert Einstein College of Medicine in New York
City had recently discovered that ingesting cyanate salts could
prevent the “sickling” of red blood cells that leads to the anemia
and pain of sickle cell disease. Dr. Jackson knew that a related
compound, cyanide, was common in foods across Africa, particularly
in the staple crop cassava (which you may know as tapioca). She was
also aware that, at the right dose, cyanide could directly protect
against the malaria parasite. She realized that regular consumption
of cassava — more common in the Southeast than the Northwest —
could, by working as an antimalarial drug, affect the prevalence of
the sickle cell trait, by making it less advantageous.
Something different was happening in the Northwest, though.
Dr. Jackson, who is now at Howard University, thinks that while
cassava consumption in the region was insufficient to protect
against malaria directly, people who had two copies of the sickle
cell gene still ate enough to partly avoid sickling. In that
population, diet may have prevented a genetic disease from fully
manifesting.
We evolved in environments that are radically different from
today’s, and some of our genes may work better in those
environments. This complicates the idea of trying to perfect the
human genome with technology. Given how much the world has changed
in just the past 150 years, and how much it’s likely to change
again in the next 150, the question is, “What environment will we
optimize our genes for?”
https://www.nytimes.com/2017/06/17/opinion/sunday/crispr-upside-of-bad-genes.html
