Final answer:
Trinucleotide repeat diseases are caused by trinucleotide repeat expansions, resulting in the production of abnormal proteins. Examples include Huntington's disease and Fragile X syndrome.
Step-by-step explanation:
Trinucleotide repeat diseases are caused by trinucleotide repeat expansions. These expansions result in the repetition of regions of the same amino acid. This type of mutation occurs when there is an increased number of copies of the same codon, leading to the production of abnormal proteins. Examples of trinucleotide repeat diseases include Huntington's disease and Fragile X syndrome.