Why do genetic mutations often impact more than one system in the body?

By genetic mutation I assume you mean a change in a gene that has been inherited from one's parents. Most often we are talking about genes that reside on DNA in the nucleus. It's important to remember that this DNA is the same in all cells of the body. Some genes are active in certain cells more than others or may be completely inactive in some, giving rise to differentiation—the wide variety of cells and tissues in the body. But many genes are active in all cells, or their mode of action may be important throughout the body.
How do genes, normal or mutated, have their effect on an organism? Genes are sequences of DNA that contain instructions for making proteins. Proteins are long chains of a kind of molecule called an amino acid. The properties of the amino acids in the chain cause the proteins to fold into three-dimensional shapes. Proteins accomplish their roles in the organism mainly because of their shapes. A mutated gene produces an abnormal protein, which may do its job poorly or not at all (rarely it will do it better).
Proteins are important because they perform so many of the functions of life. Proteins in muscle fibers change shape, causing muscles to contract and relax. Enzymes are proteins that catalyze the reactions of life, making substances we need, breaking down things we don't, and so on. Hormones are proteins that communicate with different parts of the organism. Receptors in cell membranes respond to hormones and start or stop processes in the cell. Hemoglobin is a protein in blood that transports oxygen from where it is plentiful to where it is not.
A mutation, producing an abnormal protein, can affect multiple systems in different ways:
If the abnormal protein is produced in more than one system, or throughout the body, it will of course affect every cell and every system that depends on it.
If the abnormal protein is required for transport or communication, it will affect all cells, tissues, and organs that would normally receive the materials or communications.
The systems of the body are interrelated, of course, so a defect in one system is likely to affect others. A defect in a digestive enzyme, for example, could impair nutrition to the entire body, stunting growth and affecting tissues and functions that depend most on the missing nutrient.
Finally, many genes and the proteins they make have more than one function. Melanin, for example, is known as a pigment in skin, hair, and eyes. But various forms of albinism, where enzymes involved in the synthesis of melanin are altered, produce defects in sight and hearing. It appears melanin may be needed for normal development of eyes and ears.
In summary, there are several ways a mutation can affect different systems of the body. Many inherited disorders have been characterized, and the impacts of the affected proteins on the body are known. Reading about them can provide insight into many aspects of the processes that make life work.


Genetic mutations often affect more than one organ system because most organ systems are not completely independent of each other. They work collaboratively together to ensure that the entire organism functions properly.
For example, a simple overview of the circulatory system will say that it is made of the heart, the blood, and the blood vessels. The right side of the heart is in charge of pulmonary circulation. Blood is being sent to the lungs, and the lungs are part of the respiratory system. If the lungs weren't there, the blood would never be oxygenated. If the blood wasn't being sent there, the lungs would have nothing to exchange their gas loads with. 
More than likely, any kind of genetic mutation occurring within a particular system will absolutely affect another system because each system works in close relation to at least one other system. The change in one system could enhance both systems, or the change could hinder the other system.
Let's use the circulatory system and respiratory system relationship. Let's say that a particular mutation caused a person to double the number of alveoli within each lung. We'll have to assume that each additional alveoli is also wrapped up in the normal capillary bed in order to ensure gas exchange between it and the blood. More alveoli and increased lung size will allow for more oxygen to be inhaled and absorbed into the blood. The higher levels of oxygen in the blood means that a person's breathing rate can stay lower for longer periods of time (during exercise for example). The heart will also maintain a lower overall heart rate because the blood is carrying more oxygen per breath. 
https://www.bbc.co.uk/bitesize/subjects/zync87h

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