Final answer:
Huntington's disease is an example of a tri-nucleotide repeat expansion disease, caused by a mutation in the huntingtin gene which leads to production of a toxic protein that damages nerve cells.
Step-by-step explanation:
Huntington's disease is an example of a tri-nucleotide repeat expansion disease. It is a neurological disorder caused by a mutation in the huntingtin gene. This mutation results in an expansion of the CAG trinucleotide repeat in the gene, leading to the production of a toxic protein that damages nerve cells.