is the study of measurable genetic changes that can be passed on to .
Is everything ‘genetic’ hereditary?
No. Not everything that impacts our genes is hereditary. Only gene mutations within our that we are born with are inherited. Our ‘genetic code’ within our germline is present in all our cell types including our reproductive cells (egg or sperm), thus they can be passed on to .
If you have a (disease-causing) for a hereditary thrombocytopenia syndrome for instance, you did not cause it and could not have prevented it. Not even with diet and supplemental changes.
Changes to our that are acquired are due to non-inherited influences, such as aging and even outside influences such as prolonged exposure to damaging UV radiation for instance. Acquired changes in our DNA usually only impact certain cells in our body and we refer to these as . These types of cause most non-inherited cancers. They cannot be passed on to because they are not present in the egg or sperm cells and were not inherited from a parent.
for somatic mutations is often done to determine the best course of treatment for targeted therapy in some conditions, such as cancer. Somatic mutations are also important in the diversity of the antibodies, T cell receptors, and B cell receptors. Somatic testing is not the same as germline testing for inherited (not acquired) germline mutations that can cause disease. It is important to be aware of the differences between germline and somatic mutations.
The environment can also impact genes by affecting . This is known as . Epigenetic changes affect the way genes are expressed but do not alter the genetic code itself. Epigenetics is often used to study variability in disorders. Researchers are now looking at whether outside influences, such as nutrition, affect gene expression and regulation.
Testing for can be done through specialized testing centers but is not available at this time for every disorder. These changes are not inherited and not usually passed on.
Basic Modes of Inheritance
How are gene variants inherited?
– If the mutation identified is ‘dominant’ that means only one allele (one copy of a particular gene, which come in pairs; one from each parent) needs to carry a pathogenic variant in order for the disease to manifest. Dominant variants are primarily inherited from one parent, but some can be de novo, meaning they can happen by chance. There is a 1 in 2 risk (or 50% chance) to pass on dominant variants to offspring.
– If the genetic disorder is ‘recessive’ that means in order for the disease to manifest both copies of the gene (or ) from each parent need to have a pathogenic variant for the same condition. If only one copy of the gene from one parent has a variant, then that person is referred to as a carrier, and is not usually affected by the disease. If both biological parents are carriers for the same recessive condition, there is a 25% risk (1 in 4 chance) to have a child affected with that particular condition.
– If the variant identified is ‘sex-linked’ that means the variant is on the X or Y chromosome, usually the X chromosome (also called x-linked). Sex-linked conditions can be inherited in either a dominant or recessive fashion.
Heredity – The study of measurable changes that can be passed on to future generations.
Offspring – your biological children (also referred to as your progeny).
Germline – the source of DNA for all the cells in the body (fusion of genetic information in sperm and egg union).
Pathogenic variant – Disease causing.
Germline variants – DNA changes that are present in all body cells, including the sperm or eggs. Changes in germline DNA can be passed on to offspring and are often inherited from parents.
DNA – Stands for Deoxyribonucleic Acid. DNA is one of two forms of nucleic acid that can be found on chromosomes within our cells. DNA is the genetic material for all cellular life forms (organisms that are made from more than one cell) and many viruses.
Somatic mutations – DNA changes not present in eggs or sperm. Somatic changes only affect certain cells or tissues and cannot be passed on to offspring as they are not inherited from parents. They are due to environmental impacts. Somatic testing is often done on tumors to determine the best course of treatment. Not all somatic mutations are pathogenic (disease-causing).
Variant – This is the same as a mutation, however, since changes in the nucleotide sequence do not always cause disease, the term ‘variant’ is more of an accepted term to use in medicine.
Genetic testing – this type of testing analyzes parts of an individual’s DNA to find changes (variants/mutations) that cause disease or confer an elevated risk to develop disease. It is a diagnostic medical test. Genetic testing can be performed using any tissue type, including blood.
Gene expression – when the information stored in our genetic code is converted into instructions for making proteins or other molecules. It is a highly regulated process and acts as an ‘on/off’ switch to control when genetic instructions are used. There are two involved processes in gene expression; transcription and translation.
Epigenetics – the study of gene expression. Epigenetic changes affect the way genes are expressed but do not affect the genetic code itself. Epigenetics is often used to study variability in disease.
Epigenetic signature – the unique way in which epigenetics influences the way the genes release the information they carry.
Dominant – A mechanism by which a genetic trait or gene mutation can be inherited. In dominant inheritance, only one allele copy (of a given gene) from one parent has a mutation.
Recessive - A mechanism by which a genetic trait or gene mutation can be inherited. In recessive inheritance, both alleles (of a given gene) from each parent have a mutation.
Alleles – The version of each gene that a biological parent passes down to their child at conception.
Sex-linked – A mechanism by which a genetic trait or gene mutation can be inherited. In sex-linked inheritance alleles (of a given gene) found on either the X chromosome or Y chromosome only are inherited from a parent(s) in either a dominant or recessive fashion. Usually, the term refers more to disorders linked to the X chromosome, sometimes called X-linked.