Introduction
Around 500 BC, ancient Greek philosophers, including Hippocrates and Pythagoras, believed that fathers’ characteristics determined those of their babies. They claimed that semen within a future father contained his essence, which then formed a new person. Fathers’ essence included all the physical characteristics with which they were born and that they had acquired during their lifetime. Even Gregor Mendel, the so-called “father of modern genetics,” had no knowledge of DNA or genes, and it took over a century after his death for scientists to sequence a human genome. (Mendel died in 1884, and scientists completed the Human Genome Project in 2003.) Humans’ knowledge of the very basis of our existence has accumulated over millennia, and only in recent years have we begun to appreciate the immense power of the gene.
If we have identified the gene as the basic unit of heredity and sequenced a human genome, what is next? Today, scientists are using genes to better understand and treat diseases.
Genetic Counseling
Genetic counseling aids families grappling with genetic disorders. It often involves analyzing the results of genetic testing, which helps patients uncover the specific genes behind their disorders. A primary immunodeficiency (PID) is one disorder whose cause and thus treatment options can be clarified by genetic testing.
PIDs are relatively rare conditions in which aspects of the immune system are missing or dysfunctional, usually if not always due to a genetic defect. If external factors cause a flawed immune system, the disorder is a secondary immunodeficiency. Most genetic defects that cause primary immunodeficiencies are inherited, but some result from spontaneous mutations during your lifetime.
Benefits
There are several reasons genetic testing can benefit patients suffering from PIDs:
1. Families can better understand how likely future generations are to experience PIDs. More specifically, prospective parents can gauge how likely their future children are to inherit their PID because the disorder stems from genetics.
2. Since scientists are collecting data on certain types of PIDs, patients can hear the experiences of others with their specific disorder, including the issues they faced and how long they survived.
3. Pinpointing the defective gene behind a PID can help medical professionals identify the most suitable type of transplant to perform. Transplants often treat the most serious PIDs, such as severe combined immunodeficiency (SCID). Bone marrow transplants transfer healthy stem cells in bone marrow, which develop into immune cells and all other blood cells, from donor to patient. Patients with some forms of SCID do not need chemotherapy prior to the transplant process in order to rebuild immunity properly.
In contrast, patients with other forms of SCID do need chemotherapy beforehand to optimize results. Additionally, after learning more about the genetic causes behind SCID, scientists have discovered that some forms of the disorder do not affect bone marrow cells, so a bone marrow transplant would be ineffective. In general, targeted treatment for PIDs has become increasingly available due to the discovery of their genetic causes.
4. Genetic testing can allow patients to undergo gene therapy, for the first step in such a process is identifying the defective gene.
Gene Therapy
Gene therapy involves inserting genetic material (such as DNA, RNA, and viruses) into a cell.
In Vivo
One type of gene therapy is in vivo, which means “inside the living body” in Latin. A vector (the vehicle that transports the corrected version of the defective gene into cells) is directly injected or infused into the targeted part of the patient, whether it be their bloodstream, one of their tissues, or their spinal fluid.
Ex Vivo
The second type of gene therapy is ex vivo, which means “outside the living body” in Latin, for a doctor removes the patient’s cells from their body before a vector genetically modifies them. The doctor prepares the patient through chemotherapy before returning the cells to their body. Chemotherapy removes the other cells from the bone marrow to make space for the transplanted ones with the new, therapeutic gene. If a patient receives gene therapy for a PID, their treatment is likely ex vivo.
Vectors
Scientists engineer viruses to act as vectors so that they no longer contain harmful particles that can replicate within patients and cause infections. One virus used as a vector is the adeno-associated virus (AAV), which contributes to mainly in vivo gene therapy. The virus infects a given cell, but it and the genetic material it carries stay outside the nucleus rather than incorporating into the nuclear DNA. Thus, if the cell divides, there is less AAV in each of the daughter cells, so doctors primarily use this vector for non-dividing cells.
Scientists also engineer retroviruses to introduce genes to cells. A retrovirus infects the given cell, but, unlike AAV, it crosses into the nucleus to integrate the genetic material it carries into the nuclear DNA. Thus, even if the cell divides, each of the daughter cells contains the original amount of the genetic material, so doctors use this approach for cells that do divide, such as bone marrow and blood cells.
Allogeneic Bone Marrow Transplant
For this procedure, the doctor prepares the patient to receive the transplant after identifying a suitable, healthy donor. Then, the stem cells from the donor’s bone marrow, peripheral blood, or umbilical cord blood are transferred. However, the patient may reject the donor’s cells or contract graft versus host disease (GVHD). Since “graft” means a transplanted tissue, it refers to the donor’s stem cells while “host” refers to the patient’s healthy tissues. GVHD occurs when the newly introduced stem cells attack the recipient’s healthy tissues after deeming them foreign.
Gene therapy is an alternative to allogeneic bone marrow transplant. An advantage to gene therapy as opposed to this transplant is that the patient donates to themselves (or the process is autologous instead of allogeneic), so their body will not reject the cells and GVHD will not occur. Thus, the patient will not have to undergo immunosuppression, which weakens their body’s ability to fight disease, to prevent GVHD. While gene therapy is more experimental, an allogeneic bone marrow transplant also has many risks, so both are reserved for patients with severe diseases. It is too early to say which approach is more effective. Nevertheless, gene therapy is clearly a useful tool in treating disease and thus showcases the healing power of the gene.
Although genes can help treat diseases when scientists regulate the process, our bodies have developed the ability to maintain their own health without human intervention.
Darwinian Medicine
An ongoing discussion within biological anthropology is how modern humans exhibit adaptations to their hominid ancestors’ environments. Darwinian medicine claims that some diseases or bodily reactions to them may serve evolutionary purposes. Some physicians and biological anthropologists believe that we medicate too quickly when we get low fevers, for fevers are our bodies’ way of getting rid of infection. Fever-induced heat strengthens immune cells while weakening pathogens and infected cells. You can read more about the overlooked benefits of fevers here.
Likewise, we should not view mild to moderate morning sickness as unnecessary or concerning. Women primarily experience morning sickness during their first trimester, when organogenesis occurs, or the fetus growing within them forms organs. Natural selection may have favored the main symptoms of morning sickness, nausea and food aversions, because they prevent women from intaking toxins harmful to this developing fetus. Loosely speaking, many of the foods available to our hominid ancestors (such as meat, plants, and tubers) contained toxins. The inability to ingest or the aversion toward such foods would have limited fetuses’ exposure to toxins. Thus, our female hominid ancestors with morning sickness would have produced healthier children with equally high levels of reproductive success.
Evolutionary Psychology
Another subfield of biological anthropology, evolutionary psychology, applies Darwinian medicine’s claim to our minds rather than bodies. In other words, according to proponents, the way human minds function serves evolutionary purposes, for they have been shaped by natural selection.
Human Mate Choice
For instance, human mate choice, a mental process, favors evolutionarily advantageous traits. As mentioned in my post on sexual selection, human males usually seek young, physically attractive females while human females usually seek powerful, high-status males. To have reproductive and thus evolutionary success by birthing and nursing babies, women must be young and healthy. Men can gauge potential mates’ health through their visual appearances, while women appraise men’s ability to support their offspring with resources by assessing their power and status.
Sexual Jealousy
More so than females, males become jealous when their mates are or are suspected to be unfaithful. How does male sexual jealousy serve an evolutionary purpose? When women have babies, the mother is obvious while, theoretically, the father is never definite. In science, this ever-present doubt is called “paternity uncertainty.” From a biological perspective, reproductive success is the main goal, and to achieve it, males must father as many offspring as possible. Since a man cannot be certain that he has impregnated his mate early in her pregnancy (before a paternity test can be conducted), he wants to control the female’s reproduction and exhibits more sexual jealousy.
Domestic violence can be a proxy variable for male/female sexual jealousy. While half of female homicide victims in the US are killed by intimate partners, only 10% of male victims are, and 85% of IPV (intimate partner violence) victims are women. These statistics showcase the higher prevalence of male sexual jealousy.
Your Brain’s Response to Emotional Stimuli
In a study described by Barbara J. King (the lecturer in The Great Courses – Biological Anthropology: An Evolutionary Perspective), scientists scanned the amygdalae of volunteers’ brains as they looked at images of frightening faces. The amygdala controls emotions such as fear. Afterward, the volunteers donated DNA, which scientists analyzed to determine which of two gene variants they carried. The gene in question transports serotonin, a chemical that sends messages in the brain.
The brains of volunteers with one variant were likely to be more stimulated by the images. The study concluded that genetics influence how your brain reacts to emotional stimuli.
A More Recent Study
In 2015, Rebecca Todd, a neuroscientist at the University of British Columbia, discovered similar findings about brain activity. Todd’s earlier research shows that those with a deletion variant of the ADRA2b gene (with missing nucleotides) responded more expressively to negative words. ADRA2b affects a neurotransmitter called norepinephrine.
In Todd’s subsequent study, participants estimated how pixelated positive, negative, and neutral images were. (The level of pixelation refers to the amount of photographic noise, which causes images to look grainy and discolored.) Those who carried the deletion variant were more likely to estimate that positive and negative images were more pixelated than neutral ones. Thus, Todd concluded that carriers exhibit emotionally enhanced vividness (EEV). Additionally, the parts of carriers’ brains that respond to “emotional relevance” were much more activated. Todd proposed that these varied responses to emotional stimuli may contribute to the varied likelihood of PTSD in humans.
Conclusion
Although our superficial understanding of genes was only recently established, a wide array of medical processes, including genetic counseling and gene therapy, have emerged since. While genes and biology were previously used to explain basic physical characteristics, evidently, they can be used to understand more complex processes, whether they be medical or mental.
Sources
- https://www.pbs.org/kenburns/the-gene/history-of-the-gene
- https://primaryimmune.org/resources/video/genetic-testing-gene-therapy-gene-editing-get-facts
- https://www.youtube.com/watch?v=GoEXNXYWNsA
- The Great Courses – Biological Anthropology: An Evolutionary Perspective
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7717216/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9838333/#:~:text=Purpose,an%20estimated%206%25%20of%20suicides
- https://med.emory.edu/departments/psychiatry/nia/resources/domestic_violence.html
- https://www.sciencedaily.com/releases/2015/05/150507135919.htm
- Feature image: https://aces.illinois.edu/news/addressing-societal-concerns-genetic-determinism-human-behavior