GAN Mutations

DNA is the building block of the gene and is made up of four chemical bases represented by the letters C, T, G and A. A combination of three of these DNA “letters” when put together makes up one DNA “word”. Each of these words is the code for a specific amino acid. The amino acids are then strung together like beads on a string and make up a protein. Proteins are the building blocks for different tissues.

Mutations are changes in a gene that are known to cause a certain disease. As of June of 2012, there are 52 known GAN mutations from 49 different families. Mutations have been identified on all 11 exons of the GAN gene. Insertions, deletions, missense (point mutations) and nonsense (stop codon) mutations have been identified.

Certain types of mutations called point mutations occur when a specific DNA letter is changed. This can result in a different amino acid being used and can result in an abnormal or non-functional protein.

For example, a normal sequence may look like the following:

Amino Acids Glutamine Serine Leucine Serine Tyrosine


When one DNA letter is changed, it may cause a change in the resulting amino acid that is used, as in the following example of a missense or point mutation:


Amino Acids Glutamine Serine Arginine Serine Tyrosine

In this case, one of the DNA “letters” which is typically a T has been changed to a G. This causes the amino acid change from a Leucine to Arginine. Therefore, the ingredients to make a protein have been altered.

Sometimes, SNPs (single-nucleotide polymorphisms) are not disease causing. There is only one SNP on the GAN gene known to not cause disease and that SNP exists in the Turkish population. All other mutations on the GAN gene that have been identified are disease causing.

A nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon resulting in a truncated or incomplete, and usually nonfunctioning protein produce.

Insertion and deletion mutations exist when extra base pairs are added (insertions) or removed, typically resulting in a nonfunctioning protein.