The hereditary material of each person is stored in the DNA. The DNA consists of many genes. Each gene contains the code for the production of a protein. Proteins are the building blocks of our bodies. Reading this code for producing a protein is a complicated process.
Each gene has been built up from exons and introns. An exon (derived from Expressed region) is a coding part of a gene and contains the information for building a protein. An intron is the region between the exons. The introns do not contain information required for building a protein.
We have two copies of each gene in our DNA, one from the mother and one from the father. People suffering from Usher Syndrome have mutations (harmful changes) in both copies of one Usher gene. A person can obtain two identical mutations from both parents. This is what we call homozygous changes. Two different mutations are called heterozygous changes. Here we discuss various types of mutations.
Over 1000 different mutations have been described for theUsher-genes. These mutations can largely be divided into differents types, being nonsense mutations, splicing mutations, deletions and insertions and missense mutations.
When producing a protein, first of all the entire gene is copied, thus creating a pre-mRNA containing both the introns and the exons. After the copying process, the introns are removed from the pre-mRNA in order to create the mRNA. The mRNA is a sort of building plan for producing a protein.
In this building plan all exons have been connected with each other. The separation of introns and exons is also called ‘splicing’. The exons form a readable text and the ‘protein production machine’ can read this information and use it to produce a functional protein. Consequently, a well-functioning inner ear and retina require correctly produced Usher proteins
The DNA is a long chain of building blocks, also called nucleotides (or bases). The nucleotides in the DNA are:
- Adenine (A),
- Cytosine (C),
- Guanine (G) and
- Thymine (T).
At first sight, the DNA seems to be a random sequence of As, Cs, Gs and Ts, but the order of these letters is highly important. In fact, the order of the letters defines the genetic code and determines whether a good protein is produced.