“Genes determine how an individual reacts to an environment which interns influence the genes itself to mutate.” As an organism, all of us consist of genes, that express a ‘character trait’. A human genome is made up of more than 20,000 genes with all humans sharing a common gene sequence. However, does it mean that all humans are similar? (1). The answer to this question is a clear ‘No’ because even though we are 99.9% similar, that 0.1% plays a vital role. This can be inferred by the fact that not even a pair of monozygotic twins is completely identical. They too have genetic differences due to epigenetics that cause these variations; which to a great extent could even build severe disorders and diseases (1). 

By the term epigenetics, we mean the change that occurs in a gene sequence which is not caused by mutations in genes but rather the environment and the surroundings influencing the genotypes and the phenotypes of the organisms (2). For example the presence of harmful chemicals and microbes, or the different climate and weather conditions. As a result, often these conditions tend to lead a patient to develop health concerns. 

Alzheimer’s disease, which is a neurodegenerative disease mainly faced by the elderly population aged 65+ is a prominent example of a health concern where both genes and environment play an equal share. APOE makes a protein that helps in the transportation of fats. However, one of its variants, APOE4 can cause the occurrence of Alzheimer’s disease more prevalent by forming plagues and tangles and preventing communication and transportation between neurons. (3). This is a similar case in PSEN- 1, and PSEN- 2 genes that also cause the development of Alzheimer’s disease before the age of 65, referred to as early-onset Alzheimer’s disease due to the rapid formation of amyloid-β (4). 

Considering the environmental conditions such as air pollution and, an unbalanced diet, they tend to increase risk, which is why, a diet with vitamins and proteins and low saturated fatty acid is highly essential (5). Sometimes stress also takes part in promoting Alzheimer’s disease. Even though there are no supporting theories and studies on it, it was found that depressive patients were at a higher risk of developing this disease. And since stress is directly related to depression, it is not wrong to say that taking high stress can increase the chances of Alzheimer’s disease (6).

To further understand the complications of the interconnectedness between genes and the environment influencing health problems, lots of studies and research have been conducted which indeed have given great insights to the concept. Amongst these, Zachary Kaminsky, a professor at Johns Hopkins University had also conducted research in 2008 with a few more researchers to understand how the differences in DNA methylation in monozygotic twins could impact human health and behavior. Since monozygotic twins arise from the same egg, they are considered quite identical however, sometimes discordance does appear due to the environment acting differently on the twins. (7)

Two 49-year-old female monozygotic twins took part in the experiment, where one was a war journalist and the other was an office manager in a law firm. At the age of 17, the war journalist twin left her home to visit a few war regions in Africa, the Middle East, and the Balkans, where she witnessed the harsh consequences of wars on a common man. For example the pain of losing a closed one. 

After a few years, she married a man with whom she did not share a romantic affair which is why they never had children. Eventually, she even got addicted to alcohol. On the other hand, her twin sister who was completely the opposite shared a good and stable relationship with her loved one, by even getting the privilege of being a mother of two children. 

Tests highlighted that the law twin showed 3 hysteria and 7 psychosomatic disorders causing her with high levels of anxiety and stress. As a result, she had more prominent psychological problems such as a lack of self-confidence and self-esteem This can be explained by the epigenetic difference in the DLX1 gene for both twins caused by DNA methylation (7). 

To conclude, although, most human diseases are caused due to genetic mutations in a single or multiple genes. Yet, in many of the cases environment acts as a stimulus in activating those disease-causing genes. 

1. Genes are units of hereditary information. A gene is a section of a long molecule called deoxyribonucleic acid (DNA). In. Available from: education.nationalgeographic.org/resource/genes/

2. Robert Feil, Mario F. Fraga. Epigenetics and the environment: emerging patterns and implications [Internet]. 2012. Available from: nature.com/articles/nrg3142

3. Raulin AC, Doss SV, Trottier ZA, Ikezu TC, Bu G, Liu CC. ApoE in Alzheimer’s disease: pathophysiology and therapeutic strategies. Mol Neurodegener. 2022 Nov 8;17(1):72.

4. Armstrong RA. What causes alzheimer’s disease? Folia Neuropathol. 2013;51(3):169–88.

5. Carol Watwood C. Alzheimer’s Disease. 2011;

6. Dolotov OV, Inozemtseva LS, Myasoedov NF, Grivennikov IA. Stress-Induced Depression and Alzheimer’s Disease: Focus on Astrocytes. Int J Mol Sci. 2022 Apr 30;23(9):4999.

7. Kaminsky Z, Petronis A, Wang SC, Levine B, Ghaffar O, Floden D, et al. Epigenetics of Personality Traits: An Illustrative Study of Identical Twins Discordant for Risk-Taking Behavior. Twin Res Hum Genet. 2008 Feb 1;11(1):1–11.