Epistasis is a genetic event where one or more genes modify or mask the expression of another gene. It is a double mutation and can cause diseases such as Alzheimer’s, adult-onset diabetes, autism, and cardiovascular disease. Treatments targeting associated genes can prevent and inhibit certain diseases.
Epistasis is a term used in the field of genetics and is defined as an event in which one or more genes in some way modify or “mask” the expression of another gene. In these cases, the gene whose traits are not expressed is called a “hypostatic” gene, while the other genes whose traits are expressed are called “epistatic” genes. In the theory of evolution and natural selection, epistasis is often considered a mutation and is included as an important factor in measuring a species’ biological “fitness” or ability to survive. The word is made up of two Greek words, “epi” and “stasis,” and literally means “an arrest.”
The concepts of epistasis and dominance can sometimes be used interchangeably, as both are similar in masking a phenotype or certain physical characteristic of a species. The difference, however, is that the latter concept is an interaction between two alleles, which are found in the same gene, but the former concept is an interaction of two completely different mutant genes. Another significant difference is that dominance is not really a mutation, but is a natural process of how an offspring inherits genes from its parent. Epistasis, however, is a genetic interaction in which all genes involved are considered “mutants”, thus a “double mutation” occurs.
A simple example of how epistasis changes a genetic trait can be seen in a horse’s red coat color, which is actually produced by a mutation in a certain gene. If the horse inherits two of these mutated genes, the red color will be kept but the shade will be lighter or darker. A masking effect of an epistatic interaction, on the other hand, can be observed when a person inherits both albinism and red hair, both of which are also mutations. A person may not have red hair as albinism would “mask” the color and the body would not produce any pigment, even in the hair.
The fact that epistasis is a double mutation doesn’t necessarily mean it doesn’t happen all that often in humans; in fact, some geneticists believe that the phenomena can cause some diseases, such as Alzheimer’s disease. In the 1990s, scientists discovered that the “apolipoprotein E4” gene increased a person’s risk of getting the disease, but not all carriers get it, leading scientists to believe that there may be other genes responsible. In the late 2000s, scientists discovered that apolipoprotein E4 interacted strongly with three other genes, causing worse effects than Alzheimer’s. Epistasis has also been observed in patients with adult-onset diabetes, as well as autism and cardiovascular disease. As a result, several studies have suggested that treatments specifically targeting associated genes can effectively prevent and inhibit certain diseases.
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