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- This disease is an example of formation of Thymine dimers.
- There are Thymine bases that are adjacent to each other.
- Due to ultra-violet radiation sometimes two Thymine bases form a dimer with each other by forming a covalent bond.
- There is an enzyme that is called Excision endonuclease.
- This enzyme recognizes the lesion and excises the Thymine dimer that is formed due to UV light.
- Other pyrimidines can also form dimers like cytosine-cytosine dimer and uracil-uracil dimer. But they are not clinically relevant.
- This disease occurs when an individual inherits a defective copy of the enzyme Excision endonuclease.
- This is a autosomal recessive disease that means that the individual must have copies of mutant genes from both parents.
- The excised part is then replaced by DNA polymerase.
- DNA ligase then comes in to repair the remaining part.
Patient will have the following symptoms:
- Patient will be very pale because he will be sensitive to UV light.
- There will be a lot of freckles on skin due to sensitivity to UV light.
- They will have multiple skin cancers and
- They will also suffer from corneal ulcerations.
- These patients have to live a vampire like life and cannot expose themselves to sun.