A mutation or gene variant can be inherited from one or both parents, but it can also occur spontaneously or due to environmental factors. We have an average of 60 new gene variants compared to our parents. In most cases, these variants are of no importance, but in certain cases they can cause illness.
If several cases of a rare condition affect the same family, and if the condition manifests at a relatively early age, these may be symptoms of a hereditary condition. Families with indications of a serious hereditary condition may be offered genetic diagnostic testing from the hospital. Such testing would examine whether the cause of the condition is a genetic mutation.
In general terms, genetic conditions are divided into two main categories:
Monogenic conditions, which are caused by a mutation in a single gene. The mutation is found in all cells of a person and can be detected by a blood test. Monogenetic conditions are grouped into a) recessive genetic conditions, where you inherit the genetic mutation from both parents and b) dominant genetic conditions, where it´s enough that you inherit the genetic mutation from one of your parents. CTD and cystic fibrosis are examples of monogenetic diseases, and it is easy to ascertain the disease with a blood test.
Complex conditions: The genes are also important for many of the common common public diseases such as cardiovascular disease, diabetes, obesity and mental illnesses. These diseases are called complex diseases and can be caused by a cumulative effect of multiple genes (polygenetic), which can also be influenced by external factors such as lifestyle and environment. It is not possible to determine a complex disease with a blood test, since mutations are only part of the reason why the disease occurs.