​Genetics Simplified - Reeve Foundation

Genes are the codes to inform a body how to develop. Characteristics are easily seen in things such as hair color and body type. Inside the body, it can be more challenging to see how genes affect individuals. Sometimes, genetic issues have external effects that can be clues to internal issues. How genes work in the body is an extremely complicated topic. Simplifying the genetic code will help us understand what happens when genes develop.

In the body, there is DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA is in every cell’s nucleus and is a mechanism for heredity, including the development, function, growth, and reproduction of every body part. It is a molecule that is made up of long, double-stranded nucleotides (called a polymer) and contains a sugar called deoxyribose. DNA can replicate on its own. RNA is responsible for the coding, decoding, regulating, and expressing of genes. RNA is a molecule of single-stranded nucleotides that contains sugar ribose. RNA does not replicate on its own.

The structure of the chromosome includes four nucleotides. These are labeled A (Adenine), T (Thymine), C (Cytosine), and G (Guanine). ATCG is known by the pneumonic: All Tigers Can Growl to help you remember them. These nucleotides are organized into long and varied stretches of material called DNA. The sequencing of the nucleotides is DNA and proteins with also some ribozymes (enzymes). They create the cells in the body. Therefore, the sequencing of the nucleotides determines what the cell will be and how it will function.

Interestingly, the differences that you see in humans are from the minor genetic differences in the arrangement of nucleotides or sometimes even from a mutation in one of the nucleotides or genes. Variants in genes are how humans and all living things adapt to environmental changes over time. Variants can be a good thing.

There are 23 chromosome pairs in every cell of the body, 46 in total. Every cell in your body contains all of these chromosomes, which is your entire genetic code. However, the part of the body only uses the chromosomes particular to that body part.

The genes of an individual are inherited from their parents. When an egg and sperm join together, genetic material (chromosomes) connect to create a new being. There are many gender characteristics on the X and Y chromosomes, including one particular pair of gender characteristics. Females pass along an X chromosome in the egg; males can pass either an X or Y chromosome in sperm. Only one sperm can enter an egg. If an X chromosome is passed in a sperm that joins with an egg, both united XX chromosomes will develop into an individual with female sexual characteristics. If a Y sperm joins with an egg, an XY chromosome will develop into an individual with male sexual characteristics. There is much more information in the genes of sperm and egg for the development of a human being.

This sounds simple enough; however, rarely does the process occur simply. Variants occur in everyone, sometimes in the egg or sperm before joining together and sometimes after fertilization. These are called inherited variants. Some occur later in life. Non-inherited variants occur at some point in the lifespan caused by environmental or lifestyle factors affecting gene duplication. These are not passed on to children. Most of the mutations will not be noticeable, but at other times, they can result in challenges in health and function.

Polymorphisms are variants in genes just from natural occurrences. These do not lead to health concerns but may explain why your child has some differences in appearance from their parents. Their children may have the results of the natural mutation of your child’s genetic code.

When genes do not have the ATCG sequencing in the correct order for the needed function in the body, if a protein is miss produced by a gene’s instruction or a protein cannot be produced, a health condition or alteration in function can occur.

There are different types of DNA variants, including base substitutions, deletions, and insertions, as well as others. Base substitutions are a basic variant where one of the nucleotides (the A, T, C, or G) is exchanged for another. For example, the spot where an A nucleotide should be is exchanged with a C. This can result in a positive effect or benefit to the individual, or a negative effect, and sometimes makes no difference at all. An example of a base substitution is sickle cell anemia. One nucleotide in the DNA is affected, leading to a chain of events in protein production, resulting in sickle cell disease. Some individuals can carry sickle cell genes but not have the disease, while others do.

Deletions in DNA are when at least one of the nucleotides is missing. There can be more missing in a group, even to the point of an entire gene missing or a gene and the surrounding genes. The instructions for protein generation are therefore missing. Some cases of Duchenne muscular dystrophy or cystic fibrosis are health issues from deletion variants.

Insertions in DNA occur when extra nucleotides are entered into a DNA sequence. This can also be one nucleotide or several. Examples of insertion DNA variant health issues are Fragile X syndrome, Huntington’s disease, myotonic dystrophy, and cystic fibrosis. Some DNA variants can be deletion/insertion combinations.

Genetic disorders can be diagnosed by observation, as in the case of Down syndrome. Some characteristics of Down syndrome can be seen such as a flattened face principally across the nose, almond-shaped eyes, small ears, and a single line across the palms of the hands. Some laboratory tests of blood, urine, or cheek swab can indicate a genetic variant is present. Most likely, genetic testing is performed, which can include molecular tests to assess gene changes, chromosomal tests to assess large-scale changes, or gene expression tests to assess if genes are turned off.

Genetic testing is done by using a blood sample to review the individual’s DNA. This can also be done prior to reproduction to see if you carry a genetic variant. Amniocentesis can be performed to assess for some genetic variants in a fetus, such as Down syndrome. Newborn babies are tested for genetic issues such as congenital hypothyroidism, sickle cell disease, or phenylketonuria (PKU). Pharmacogenetics is used to examine your genes for medical treatment. This can be done for many diseases but is probably best known in cancer treatment, where the genetic variant of the cancer is treated by specified medications. To review the genetic variant in a family, a genetic family tree may be created to see how the gene variant passes through a family.

If there is a genetic issue, you can consult with a genetic counselor to see if you can pass the gene variant to your child. You may be provided with a risk estimate or the odds that you will pass the gene variant. Not all gene variants pass to children, but also having a low risk does not mean that you will not. Genetics is not one hundred percent predictable without clear-cut outcomes.

Treatments for genetic issues vary. Some will not require any intervention. Others will receive therapy and medication as needed. Today, as the human genome has been mapped, there are a variety of options for genetic therapy for some health issues. Gene therapy as a treatment is growing every day. In this treatment, a new gene may be introduced, or an altered copy may be introduced into the body to replace or supplement the function of the gene variant or that can turn on or off a gene. Some gene therapies are available now, such as for treating cancer, heart disease, cystic fibrosis, hemophilia, and AIDS. Only some cases of these conditions are eligible, but many more options are being discovered and refined daily.

Linda Schultz is a leader, teacher, and provider of rehabilitation nursing for over 30 years. In fact, Nurse Linda worked closely with Christopher Reeve on his recovery and has been advocating for the Reeve Foundation ever since.