**Core Concept**
Trinucleotide repeats refer to a type of expansion mutation where a specific sequence of three nucleotides is repeated multiple times in a gene. This phenomenon is associated with various neurodegenerative disorders, including Huntington's disease, Fragile X syndrome, and spinocerebellar ataxias.

**Why the Correct Answer is Right**
Trinucleotide repeats lead to the expansion of a specific sequence, causing the gene to become unstable and leading to the production of toxic proteins that can cause cellular damage. This is often due to the expansion of a CAG repeat in the Huntingtin gene in Huntington's disease, or an expansion of a CGG repeat in the FMR1 gene in Fragile X syndrome. The expanded repeats can cause the gene to become hypermethylated, leading to its silencing and the subsequent loss of normal gene function.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because trinucleotide repeats are not typically associated with mitochondrial DNA mutations, which are characterized by point mutations or deletions.
**Option B:** This option is incorrect because chromosomal translocations involve the exchange of genetic material between non-homologous chromosomes, which is distinct from the expansion of trinucleotide repeats.
**Option C:** This option is incorrect because point mutations involve changes to a single nucleotide, which is different from the expansion of trinucleotide repeats.

**Clinical Pearl / High-Yield Fact**
Trinucleotide repeats are a type of expansion mutation that can cause a range of neurodegenerative disorders, and the number of repeats can often predict the severity and age of onset of the disease.

**Correct Answer: D.**