Genetics

 

Many families who have a child with congenital heart disease ask why their child was born with the condition. In some cases the malformation will have occurred because of a genetic problem that has affected the heart as it formed in the womb.

 

 

When a new house is built the architect draws up a plan of what the house will look like and how it is going to be built.

 

When a new child is being created, information is drawn from the mother and the father to make a plan of how the child will look and how their body will be put together to work.

 

 

Every person in the world has a genetic blueprint of their own. The blueprint is stored in every cell in their body and holds the information required to help the body grow, develop and work properly. The information is made up of lots of messages which we call genes. We have about 30,000 genes in each cell of our body. Different genes have different messages that are responsible for instructing our body to do specific things. For instance, genes determine the colour of our hair or eyes or how cells work in different organs, for example the liver, heart or lungs. It is our very own information computer.

 

The genes are stored in coils and split into chromosomes. Humans have 23 pairs of chromosomes, so 46 in total. 23 chromosomes (one of each pair) come from the mother and the other 23 from the father. They are transferred in the egg and sperm that make a child.

 

The picture below shows what the chromosomes look like - if you look at the last set of chromosomes on this picture you will see that they are labelled X and Y. These are the chromosomes that decide if you are male or female. The chromosomes below must come from a man because there is an X and a Y chromosome. A woman has two X chromosomes.

 

 

 

Some congenital heart conditions are linked to a genetic disorder such as Down's syndrome or 22q Deletion. These disorders are caused when one of the 46 information chromosomes is malformed. As the baby grows in the womb, the genetic malformation will cause a particular part of the heart to develop incorrectly. In some cases the genetic condition can be detected before birth.

 

Geneticists (genetics doctors) are always looking for genetic causes for congenital conditions, however there are many heart conditions that do not have a specific genetic cause. Many of the single working ventricles fall into this group.

 

There may be many factors, as yet unknown, that cause a baby's heart to develop abnormally. The problems can occur early in pregnancy as the heart forms or later as it grows.

 

Congenital heart conditions occur in 1 in 100 pregnancies. If you have previously had a child with a single ventricle heart problem the risks of it happening again to parents, brothers or sisters, or the child themselves rises between 5 and 8%. Although the risk is higher, over 90% of future babies will not have a problem with their heart.

 

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