• Genes carry our genetic code.
• This code is stored on DNA, which is organised into chromosomes and kept in every cell of our body.
• Our genetic code is passed down to us from our biological parents, and it makes us who we are.

• Genes tell our bodies to make proteins.
• Proteins are found in every one of our cells and play critical roles in our bodies.
• The sequence or code of each gene tells our body how to make a particular protein.
• Proteins are made up of long strings of building blocks called amino acids. There are 20 different amino acids that can be used to make different proteins.
• Amino acids are joined together one-by-one to form proteins according to the instructions in each person’s genetic code.

A pathogenic variant is a change in a gene that either causes a health condition or makes it more likely that a health condition will develop.

A nonsense variant is a change in the genetic code that adds an early ‘stop’ signal to the gene. This tells the cell to stop adding amino acids to the protein chain earlier than usual.

The result is a shortened (truncated) protein instead of the usual full-size protein. This shorter protein may be destroyed by the body or it may not work.

When there is a missense variant in a gene, one amino acid building block is replaced with another in the protein that is produced from the gene. Although it is only a small change in the protein, the change may have a big impact on the way the protein works.

• As described above, when there is a change in a gene, it can affect the way the product of the gene – the protein – works.
• When the protein is more active than usual, the genetic change is called a gain of function variant.
• When the protein is less active than usual, or does not work at all, the change is called a loss of function variant.
• Both of these types of variants can cause health conditions. 

• Mosaicism is a special type of genetic variation.
• Usually, all the cells in a person's body (except the eggs or sperm) have the same genetic makeup.
• People with mosaicism have a mixture of cells with different genetic information.
• This means some cells in the body may have a variant that causes a health condition, while the rest do not.
• Mosaicism may be seen across the whole body or only in a certain part of the body.
• When mosaicism only occurs in the eggs or sperm cells, it is called gonadal or germline mosaicism.