Role of Genetics in Health and Disease

Genetics plays a role in many human diseases, including birth defects, developmental disabilities, and cancer. These disorders may be caused by changes in a single gene (monogenic), by mutations in multiple genes (multifactorial inheritance disorder), or by damage to chromosomes.

Complex diseases involve changes in several genes and/or environmental factors. They are often called multifactorial because of the number of different things that can be responsible for a person’s disease.

Genes

Genes play a central role in health and disease. They are the instructions that direct the making of proteins, which have a vital role in human survival and growth. Genetics can affect how and when a person ages, how they feel, what they look like, and whether they develop a disease or not.

Every living thing has genes. These genes are made up of DNA, which is the building block of all our cells. This DNA is composed of chains of nucleotides that wind around each other to resemble a twisted ladder. The rungs are formed by bonded pairs of nitrogenous bases, such as adenine (A), guanine (G), cytosine (C), and thymine (T).

A gene is a small section of DNA that is responsible for the hereditary characteristics or phenotype of an organism. It contains nucleotides that specify a specific protein or RNA molecule.

The gene is a basic unit of inheritance, and it is passed on to children by their parents. Changes in a gene are called mutations. These changes can be inherited, or they can happen spontaneously during formation of an egg or sperm.

Variations in a single gene can cause an illness. These variations can be inherited from each parent or they can be acquired (meaning that they occur during a person’s lifetime).

Some diseases, such as cancer, are caused by more than one gene and are referred to as complex diseases. They are also known as multifactorial diseases because they include genetic and environmental factors.

Many diseases are caused by mutations, or changes in a gene’s sequence of bases. The sequence of the bases determines how the gene works and how it will make a protein. These differences are usually tiny, but they can have a big impact.

Luckily, most mutations have no effect on health and are harmless, but some of them can make certain proteins work differently or not at all. Some of these variants can lead to serious diseases. These diseases are called hereditary conditions, and they can have serious effects on a person’s health and life.

Proteins

Proteins are large molecules that perform many critical functions in cells. They also help the body fight disease and provide structure to tissues and organs. They can be found in meats, dairy products and vegetables.

A protein molecule is made up of many different amino acids joined together by peptide bonds to form a long chain (like beads arranged on a string). The specific number and sequence of amino acids determines the function of a protein.

Most proteins are very similar in their amino acid composition, but the way they fold into a specific 3D structure can vary widely between species and organs. These differences are usually a result of the nucleotide sequence of their genes.

Humans have about 20,000 genes on 23 pairs of chromosomes, and new ones are being discovered all the time. Genetics research aims to understand how these genes change and how these changes affect health and disease.

Each gene contains instructions for building one or more molecules that are needed to make our bodies work. The DNA that makes up a gene is shaped like a corkscrew-twisted ladder with backbones and rungs of four base pairs — adenine, thymine, guanine, and cytosine.

The base sequences of these bases give us the instructions to build proteins and other chemicals that our cells use to make and maintain their structures, carry out chemical reactions, and respond to stimuli. These instructions are passed from parent to child through a process called heredity.

These changes in our genes can affect how we look, how well our teeth and eyes grow, what kind of foods we eat and what diseases we develop. They can also affect how our bodies build the proteins we need for good health.

Because of the diversity in our chromosomes, each cell in our body has its own set of genes. These genes are switched on or off according to the needs of that particular cell.

Proteins are folded into their final, unique and compact structure by thousands of noncovalent bonding interactions between amino acids. These interactions help them survive and fold into their shape, which is determined by how they are bonded to other proteins and to the cellular environment.

Mutations

Mutations are changes in the DNA sequence, which can have a positive or negative effect on health and disease. These mutations can be inherited from one parent to another (“hereditary”) or they may occur during a person’s lifetime (“acquired”).

Most mutations are harmless, and the body can repair them. However, some mutations can cause diseases like cancer or heart disease. These are called genetic diseases.

Often, these diseases are caused by genes that control growth and development. For example, sickle cell disease is caused by a mutation in the gene for hemoglobin on chromosome 11. This changes the code for making the protein to add the amino acid valine instead of glutamic acid.

This change affects how red blood cells are made, causing the red blood cells to become an abnormally rigid and sickle-shaped shape. It also can make people prone to malaria.

Other mutations are larger and affect more than a single nucleotide in the DNA. These are called large-scale mutations and are classified into amplifications (also referred to as gene duplications), deletions of large chromosomal regions, and chromosomal inversions.

Small-scale mutations involve one or a few nucleotides and are further classified into substitution mutation, insertion mutation, and deletion mutation. Typically, these are “conservative” or “nonconservative” changes. A change in a codon that specifies a different amino acid is called a missense mutation.

Sometimes these mutations cause a change in the resulting protein structure or function, but not a significant one. This is called a silent mutation, and people with these changes may not even realize they have them.

There are many other kinds of mutations, including nonsense mutations, frameshift mutations, and random substitutions of base pairs. These mutations are important in the evolution of species because they can change the way a protein or polypeptide is read by the DNA coding machine, which can change how a protein or polypeptide functions. They can also affect how the gene is turned on and off, which in turn can influence the physiology of an organism.

Treatments

Genes are the instructions our DNA gives our cells to make proteins that help keep us healthy. Sometimes, though, our genes can be changed (mutated) by other things in our environment and these changes can cause disease.

Treatments can be used to slow or stop the progression of genetic diseases. This is called gene and cell therapy. It has shown promise in treating many rare and severe diseases that were otherwise fatal without treatment. Early research shows that if these treatments are received in the early stages of disease, they can slow or stop the development of the disease altogether.

Another treatment is gene inhibition therapy, which stops the activity of a faulty or missing gene that causes a disease. It can be a very effective treatment for some cancers that are caused by a faulty gene.

This type of therapy uses a special kind of virus to introduce DNA into the body to correct a faulty gene. The new DNA usually contains a normal version of the faulty gene and improves the way the cells work.

There are two types of gene therapy: in vivo and ex vivo. In in vivo approaches, cells from the patient’s body are extracted and re-engineered in the lab. These cells can then be injected into the person’s body to treat a disease.

Several different kinds of gene therapies are in clinical trials, many for rare conditions. A few have been approved by the U.S. Food and Drug Administration for use in patients with B-cell acute lymphoblastic leukemia and multiple myeloma. Others are being evaluated for the treatment of lipoprotein lipase deficiency and severe combined immune deficiency.

These gene and cell therapies can be very effective in treating many serious and life-threatening diseases that were previously considered fatal without treatment. They can be given at an earlier stage of the disease, which can help delay or prevent disease complications and damage to vital organs such as the heart, kidneys and eyes.

Because gene and cell therapies can be very costly, they are not generally used in routine medical care. However, they can offer hope for the future and reduce medical costs for people with these severe, life-threatening diseases.