What are genotypes?

The section of chromosome 7 that is responsible for making the CFTR (a protein) contains 1,480 amino acids (amino acids are the parts that make up a protein. The CFTR is a protein). A mutation can occur to any one of these amino acids that will affect the function of the CFTR. There are over 1, 500 different types of known CF mutations, not all of which cause disease.

Genotypes are the names of the mutations that are the differences in the DNA of a person with CF. Everyone with CF will have 2 mutations - 1 from their mother and 1 from their father. The most common ones in Australia which 95% of people with CF have are DF508, G551D, G542X, R117H, R553X and 621+1. The different genotypes can be divided into different groups (classes) based on how they affect the CFTR. There are 5 different classes (or groups) of mutations.

What genotype you have gives no indication of the severity of CF lung disease. Children from different families with the same genotype may have different severities of disease. Even two children (or twins) from the same family who have the same genotype may have very different lung disease.