Which genes are more dominant

Autosomal Dominant Inheritance: Information for Patients and Their Families

Below is some information about what an "autosomal dominant inheritance" is and how autosomal dominant disorders or diseases are inherited. To understand autosomal dominant inheritance, it is helpful to first learn about genes and chromosomes.

Genes and chromosomes

Our body is made up of millions of cells. Most cells contain the full set of our genes, the entire human genome. We have thousands of genes. Genes give the instructions that regulate our growth and body functions. They are responsible for many of our properties, such as eye color, blood group or size.

The genes are located inside the cell nucleus as tightly twisted structures called chromosomes. As a rule, we have 46 chromosomes in most cells. We inherit the chromosomes from our parents, 23 each from our mother and father, so we have two sets of 23 chromosomes each, or 23 pairs of chromosomes. Because chromosomes are made up of genes, to be on the safe side we get two copies of most genes, one copy from each parent. That is why we often have characteristics similar to our parents. The chromosomes and genes consist of a chemical substance, DNA (DNA is the English name for deoxyribonucleic acid).

Sometimes it happens that a change (mutation) occurs in one of the copies of a gene, which affects its function. Such a change can be the cause of a genetic disorder or disease because the gene no longer provides the correct information to the body.

Fig.1: Genes, chromosomes and DNA

What does "autosomal dominant inheritance" mean?

Some genetic disorders or diseases are inherited in a "dominant" manner in a family. This means that someone inherits both an unchanged copy of a gene and an altered one. If, however, the changed copy prevails over the unchanged copy, it becomes "dominant" over this. This is the reason that this person is affected by a genetic disorder or disease. The way in which this disorder or disease affects itself depends on which instruction the modified gene should actually have given the body.

Some of the autosomal dominant genetic disorders or diseases appear from birth, others only in adulthood. These are referred to as "late-onset genetic disorders or diseases". Autosomal dominant genetic disorders or diseases are, for example: the cyst kidney (polycystic kidney disease) and Huntingdon's disease.

How are autosomal dominant genetic disorders or diseases inherited?

Fig.2: Inheritance of autosomal dominant genetic disorders or diseases.

If a parent has an altered gene, either the unchanged or the altered gene can be passed on to the child. Each of the children has a 50% (or 1: 2) chance of inheriting the changed gene and thereby the disorder or disease.

The probability that the child will inherit the unchanged copy of the gene is also 50%, or 1: 2. When that happens, the child is not affected by the disorder or illness and cannot pass it on to their own children.

These possible results come about purely by chance (randomized). The probability of each occurrence remains the same for every pregnancy. It is the same for both boys and girls.

Why does a genetic disorder or disease sometimes seem to skip a generation?

Some autosomal dominant genetic disorders or diseases can affect family members to different degrees. This is called "variable expression". In fact, the generation is not skipped at all. Rather, the symptoms of the disorder or illness are only very weak in some sufferers, so that they appear unaffected. Often those affected do not even know that they have the disorder or illness.

In the case of genetic disorders or diseases that only occur in adulthood - so-called late-onset disorders or diseases such as: hereditary breast cancer or Huntingdon's disease - those affected may already have died due to other causes, so that the disorder or disease could no longer occur. In such cases, however, the genetic disorder or illness may already have been passed on from the parents to the children.

What if someone was the first in a family to have the disorder or illness?

Occasionally, someone may be the first in a family to be born with an autosomal dominant genetic disorder or disease. This can be the case when a change in a gene has occurred for the first time, either in the egg or sperm cell that led to the emergence of this child. In such a case, the parents of that child are not affected. It is also very unlikely for these parents to have another child with this disorder or illness, but you should always discuss the risk with your doctor. An affected son or daughter who now carries the modified gene can pass it on to his or her children.

Examinations during pregnancy

For some autosomal dominant genetic disorders or diseases, there are test methods that can be used during pregnancy to determine whether the child has inherited the disorder or disease (for more information about these methods, see the information sheets on "Chorionic villus sampling" and "Amniocentesis"). In any case, you should seek advice from your doctor.

Behavior towards relatives and other members of the family

If any member of your family has an autosomal dominant genetic disorder or disease, you should let the other relatives know about it. This information can help diagnose additional family members who have the disorder or disease. It would be especially important for those relatives who already have children or who would like to have children in the future.

Some people find it difficult to inform relatives about their genetic disorder or illness. (For example, you do not want to arouse fears in the family. In other families there is hardly any contact between relatives, which makes contact difficult. Doctors in human genetics usually have a lot of experience with families in these situations and can support you in dealing with them Discuss problems with family members and relatives.)

What you should always remember!

  • With an autosomal dominant inheritance, one only needs to inherit one copy of an altered gene to be affected by a genetic disorder or disease (50% probability). The respective result occurs purely by chance. The risk remains the same for every pregnancy. It's the same for both boys and girls.
  • A changed gene cannot be repaired - it is retained for life.
  • An altered gene is not contagious. You can therefore still donate blood, for example.
  • Some people develop guilty feelings about a genetic disorder or disease that runs in their family. Always remember: Nobody was responsible for the occurrence of the disorder or caused it by their behavior.

This is only a brief description of the autosomal dominant inheritance. Further information can be obtained from the following addresses:

The children's network

Web: www.kindestetzwerk.de
Service phone: (0 60 21) 1 20 30

Alliance of Chronic Rare Diseases

Web: www.achse-online.de
Email: [email protected]
Service phone: 0180-5-ACHSE-5 or 0180-5-22473-5

German Society for Human Genetics e.V .:

Web: www.gfhev.de

Orphanet

Freely accessible website; there you will find information on rare diseases, clinical studies, drugs and links to patient groups across Europe.
Web: www.orphanet.de

EuroGentest

Free access website containing information on genetic testing and links to patient groups across Europe.
Web: www.eurogentest.org

Or at a human genetic university institute or at the genetic counseling center there:

www.gfhev.de/de/hochschulinformationen/humangenetisch_einrichtungen.php
www.gfhev.de/de/beratungsstellen/beratungsstellen.php

Credits

Edited information sheet published by Guy’s and St. Thomas’ Hospital, London and the London IDEAS Genetic Knowledge Park, according to their quality standards.

January 2008

This text was prepared with the support of EuroGentest, a Network of Excellence funded by the EU-FP6, contract no: E 512148

Translation: Prof. Dr. R. Peter Nippert.

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