Difference between genetic and hereditary diseases

When we discuss genetic diseases or hereditary conditions, there is often confusion between these terms. Ultimately, both “genetic” and “hereditary” refer to our DNA and our genetic make-up. However, we need to make the difference between genetic and hereditary, as the two terms are not necessarily interchangeable.

While both genetic and hereditary diseases are determined by mutations in our DNA, not all genetic diseases are transmitted down the family line. Only those that are transmitted from generation to generation are hereditary.

Difference between genetic and hereditary disease: Key definitions

All hereditary diseases are genetic, but not all genetic diseases are hereditary. To understand the differences between these two concepts, we must first look at the definitions and characteristics of each.

Genetic diseases are pathologies that occur because of an alteration in our genetic material or DNA. Mutations can be caused by an error in DNA replication or by environmental factors (e.g. cigarette smoke or exposure to radiation). In this case, the disease can manifest itself at any age. Genetic diseases may be transmitted by parents to their offspring or not.

A hereditary disease is caused by alterations in the genetic material, transmitted from parents to children. While there is also a change in the DNA, the key characteristic here is the fact that the disease is transmitted, because the alteration is presence in all the cells of the organism including in the germline cells as we will explain below.

We know that DNA is transmitted from one generation to the next, so the question is how some genetic diseases avoid becoming hereditary. To understand this, we need to first look into DNA briefly.

A brief overview of our DNA

DNA (deoxyribonucleic acid) is a complex molecule that forms the building block for our genetic makeup. It can be found in virtually every cell of our body, and it contains the instructions needed to create and maintain life.

Our genome (the entire set of our DNA) can be considered the “genetic book of life.” This is where we’ll find our genes, sections of DNA that give rise to the proteins that carry out various functions in our body. Interestingly, only 2% of the DNA leads to the creation of proteins.

DNA is a very long molecule, which is often represented as the helicoidal shape we’re all very familiar with. The DNA together with other molecules forms what is known as chromatin. When cells divide, chromatin is compacted to its maximum, and this is what creates chromosomes. Humans have 23 pairs of chromosomes. In each pair, we inherit one chromosome from our mother and one from our father, for a total of 46 chromosomes.

Genetic alterations: What are they and how do they come about?

From the moment the egg is fertilized, and a zygote is formed, our DNA is defined, and we have the 46 chromosomes we mentioned above. While cells divide constantly throughout our lives (giving rise to new cells), it’s during the embryonic development that they divide at the fastest rate.

Since cells are dividing quickly during embryonic development, the genetic material contained within them is also divided, synthesized and distributed among the new cells. The result is that we’ll have two daughter cells completely equal to each other stemming from the original cell. This process is called mitosis.

Mitosis is a very efficient mechanism, which includes a number of checkpoints along the way to verify the process is continuing correctly. However, the possibility still exists that errors occur in the DNA sequence, which escape these checkpoints. These are known as DNA mutations or genetic alterations.

A DNA change does not always imply disease. In some cases, a change has no implication, while other changes affect the structure of the protein coded by the gene, causing a disease.

So, what makes the difference between genetic and hereditary, given that either occur as a genetic alteration? The key to answering this question is when and where the alteration takes place.

Germ line and somatic cells: the real difference between genetic vs hereditary diseases

We need to look at one more distinction between our cells before we can fully understand the difference between genetic and hereditary diseases. This refers to two types of cells: germ line vs somatic.

Germ line cells

Germ line cells are the sex cells i.e. the eggs and sperm. They are the cells that transmit DNA to the next generation, and they are the key to sexual reproduction. Importantly, the DNA contained in the germ line cells are the only ones passed from the parent to the child. This is how the genetic information is transmitted.

If the parent has a mutation in their germ line cells, their eggs or sperm will be affected by it, carrying it through with them in the new cells of their child. If the mutation in question is one that causes a disease, this will be a hereditary disease.

Somatic cells

Apart from the eggs and sperm, all other cells are the somatic cells. Any DNA mutations in this type of cells will determine genetic diseases, but they won’t be hereditary because they are not transmitted to the person’s offspring.

A good example of how hereditary diseases work is the case of some hereditary cancers. Researchers have discovered that there are many genes that help repair DNA to prevent, for example, breast cancer. The most known genes involved in the development of breast cancer are: BRCA1 and BRCA2. Having a mutation in BRCA1 gene increases the risk of developing breast cancer by up to 87%, a very high risk compared to the general population risk of 12%. If a person has a mutation in BRCA1 gene in their germline cells, this mutation could be passed on to their offspring, who will inherit this increased risk of breast cancer.

Hereditary cancer represents about 5-20% of all cancers, while the most common cause of cancer are acquired mutations that appear in somatic cells. They can appear throughout a person’s life and are more frequent as we get older, leading to a tumour growth. That being said, the key difference between genetic and hereditary disease lies in whether the gene mutation causing the disease is present in the germ line cells or not. Ultimately, mutations in the germ line lead to hereditary diseases, while mutations in the somatic cells lead to genetic diseases which are not hereditary.

At Veritas, we offer myGenome, the whole genome sequencing service and interpretation intended to help prevent hereditary diseases and improve your health. The test provides key genetic information to the patient and his or her physician in order to adapt the individual’s lifestyle and medical care. myGenome is the most comprehensive preventive genetic test for healthy patients that look up for germ line mutations and much more. Don’t hesitate to contact us for more details.