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Genetic disorders are inherited across generations. In some instances, only one parent passes down the defective gene, resulting in carriers of a genetic disease. Research has shown that some carriers of specific genetic conditions have increased resistance to certain viral or infectious diseases. While many genetic disorders can be severe, there may be advantages to being a carrier or having full-blown symptoms of a condition. Similarly, infection with particular pathogens sometimes provides immunity to other illnesses in the future.
The following conditions have demonstrated the ability to provide some level of resistance to other diseases. Some of the viruses mentioned remain untreatable, but understanding the factors that give individuals immunity to these pathogens can aid researchers in finding better treatments. Here are ten diseases that provide protection against others.
10. Sickle-Cell Disease and Malaria
Carriers of the sickle-cell gene have been shown to have increased resistance to malaria. Sickle-cell is a genetic disorder where the red blood cells become misshapen, turning crescent-like and more prone to clotting. According to the Centers for Disease Control, 60 percent of individuals who carry the sickle-cell gene survive malaria. As a result, regions with high malaria prevalence, such as Central and South America, Africa, Asia, and the Indo-Pacific, also have significant numbers of sickle-cell carriers.
The way sickle-cell provides protection against malaria involves a component of hemoglobin called haem. Low levels of haem activate haem oxygenase-1, which in turn breaks down haem. This breakdown produces increased levels of carbon monoxide in the bloodstream, as haem oxygenase-1 releases carbon monoxide, a substance crucial in malaria prevention. A group of scientists tested this on mice and observed these findings.
9. Tay-Sachs Disease and Tuberculosis
Carriers of the Tay-Sachs gene have demonstrated a level of protection against Mycobacterium tuberculosis, the bacterium responsible for tuberculosis. Tay-Sachs disease damages neurons in the brain and spinal cord, and it is more prevalent among Ashkenazi Jews, likely due to historical segregation and limited immigration within this group. A clear link has been established between the spread of the Tay-Sachs gene and tuberculosis in this population.
Tay-Sachs carriers produce a specific subunit of the enzyme hexosaminidase, which plays a key role in preventing tuberculosis. This subunit helps eliminate Mycobacteria and reduces the activity of other bacteria on the surface of cells. Despite the higher rates of tuberculosis among Ashkenazi Jews, the mortality rate from the disease is lower due to this protective mechanism.
8. Cystic Fibrosis and Cholera
Carriers of the cystic fibrosis gene have been shown to survive Vibrio cholerae, the dangerous strain of cholera. Cystic fibrosis causes thick mucus to accumulate in the respiratory system, blocking airways and creating conditions for bacterial growth in the lungs. It also obstructs digestive enzymes in the small intestine, preventing proper food digestion. However, cystic fibrosis carriers do not typically experience the full symptoms of the disease, and they may also be less affected by cholera.
Cholera is deadly because it leads to the loss of up to 19 liters (5 gallons) of water per day, causing severe dehydration. Cystic fibrosis affects chloride channels, helping retain fluids in the body. As a result, even cystic fibrosis carriers infected with cholera lose significantly less fluid, enough to flush out the cholera toxins from the intestines without becoming dehydrated. Thus, possessing just one cystic fibrosis gene can prevent the life-threatening dehydration associated with cholera.
7. Cystic Fibrosis and Tuberculosis
As reported by New Scientist, while cystic fibrosis does offer protection against cholera, the disease wasn't fatal enough to fully explain the widespread presence of the cystic fibrosis gene. Between the 1600s and 1900s, tuberculosis accounted for about 20 percent of deaths in Europe. This likely explains the high number of cystic fibrosis gene carriers, as they survived long enough to pass on their genes. However, those with two cystic fibrosis genes typically didn't live long enough to pass on their DNA, similar to many who succumbed to tuberculosis.
On the other hand, individuals with just one cystic fibrosis gene have exhibited some level of resistance to tuberculosis, which is why the gene remains prevalent among Europeans and their descendants. Though the cystic fibrosis gene could have disappeared over time, it has endured for thousands of years, suggesting that it must serve some useful purpose. This purpose is believed to be its ability to offer resistance to tuberculosis.
6. Cowpox and Smallpox
Cowpox, a viral skin infection, is essentially a less severe form of smallpox. While cowpox isn't exactly enjoyable to experience, the human body is able to halt the infection's progression after a certain period, preventing it from becoming fatal. Cowpox provides protection against smallpox because both illnesses are fundamentally similar.
When exposed to the cowpox virus, the immune system builds immunity against it. This makes it easier for the immune system to combat a more dangerous version of the virus later on. Edward Jenner famously used cowpox to create the smallpox vaccine in the late 1700s.
5. Phenylketonuria and Mycotic Abortions
An online study has found that "Physicians observed that women who were PKU [phenylketonuria] carriers had a much lower than average incidence of miscarriages." PKU is a genetic disorder in which phenylalanine accumulates in the body, leading to complications when the patient consumes a large amount of protein. The body suppresses the production of an enzyme that breaks down this substance, and the buildup can be fatal.
While PKU can lead to severe health complications, those who carry the gene seem to have a protective advantage when it comes to mycotic abortions, or pregnancy losses caused by fungal infections. This is especially common in Scotland and Ireland, where the climate fosters the growth of fungi, some of which are responsible for mycotic abortions. The phenylalanine that accumulates in PKU carriers helps combat the major toxins produced by many fungi that trigger spontaneous miscarriages. As a result, carriers are better able to ward off these infections and safeguard their unborn children.
4. Myasthenia Gravis and Rabies
There is a connection between individuals with myasthenia gravis and a reduced risk of contracting rabies. Myasthenia gravis is a condition that weakens the voluntary muscles due to faulty communication between the nervous and muscular systems. Rabies typically spreads through the nervous system by infecting the skeletal muscles, as it is often transmitted through animal bites.
Since rabies commonly enters the muscular system through a bite, individuals with myasthenia gravis have a higher level of protection against the disease. Their faulty muscle-to-nerve connections make it harder for the rabies virus to infect the nervous system in the first place. Though muscles are not the only entry point for rabies, they are a key one for the peripheral nervous system, which helps delay or prevent the infection until medical help can be sought.
3. Congenital Disorder of Glycosylation 2b and Viral Infections
Congenital disorder of glycosylation 2b (CDG-IIb) is an extremely rare condition that has been found to offer protection against several viral infections such as HIV, influenza, herpes, and hepatitis C. This disorder works by disrupting the activity of the enzyme mannosyl-oligosaccharide glucosidase (MOGS), which plays a crucial role in the processing of N-linked oligosaccharides.
Essentially, the defective glycoprotein synthesis in CDG-IIb patients prevents viruses from reproducing since they rely on proper glycosylation for replication. Without functional glycosylation, these viruses cannot thrive. Research reveals that individuals with CDG-IIb show typical immune responses to viruses that do not replicate, but they fail to respond to live vaccines for viruses that depend on glycosylation for reproduction. Additionally, MOGS inhibitors can block the replication of infected cells, preventing the spread of enveloped viruses.
2. Niemann-Pick Disease and Marburg
Similar to the Ebola virus, Niemann-Pick disease enhances resistance to Marburg. Marburg, a filovirus like Ebola, is notorious for its high fatality rate. It leads to hemorrhaging and severe shock syndrome, primarily affecting humans and nonhuman primates.
In a manner akin to its effect on Ebola, Niemann-Pick disease imparts resistance to Marburg by causing a deficiency in NPC1, a protein essential for the replication and spread of filoviruses. Since these viruses cannot propagate without NPC1, patients with Niemann-Pick disease are better equipped to combat Marburg, as it becomes non-lethal in the absence of viral replication.
1. Niemann-Pick Disease and Ebola
Niemann-Pick disease is characterized by the abnormal accumulation of cholesterol within lysosomes. This buildup occurs due to a shortage of the NPC1 protein, which is responsible for transporting cholesterol out of lysosomes. Research has shown that NPC1 plays a key role in the Ebola infection process. The Ebola virus infects the fibroblasts of Niemann-Pick patients poorly, while it infects fibroblasts with abundant NPC1 more effectively.
The Ebola virus struggles to infect individuals with Niemann-Pick disease, as the absence of NPC1 makes it significantly harder for the virus to penetrate and infect the cells.
