Trinucleotide repeat is seen in
**Core Concept**
Trinucleotide repeats are a type of genetic mutation characterized by the expansion of a short sequence of three nucleotides (a trinucleotide repeat) that occurs in a gene. These repeats can lead to a range of diseases, including neurodegenerative disorders, due to the disruption of gene function and protein production.
**Why the Correct Answer is Right**
Trinucleotide repeats are a hallmark of diseases such as Huntington's disease, where the expansion of a CAG repeat in the Huntingtin gene leads to the production of an abnormal protein that causes neuronal degeneration. The mechanism involves the expansion of the repeat, which disrupts the normal function of the gene and leads to the production of a toxic protein that causes cell death. This is a result of the abnormal protein's interaction with other cellular proteins and its aggregation in the cytoplasm, leading to neuronal dysfunction and death.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because trinucleotide repeats are not typically associated with chromosomal translocations or deletions.
**Option B:** This option is incorrect because trinucleotide repeats are not primarily related to point mutations or single nucleotide substitutions.
**Option C:** This option is incorrect because trinucleotide repeats are not typically associated with viral infections or prion diseases.
**Clinical Pearl / High-Yield Fact**
Trinucleotide repeat disorders are a group of genetic diseases that are often characterized by an autosomal dominant pattern of inheritance and a late-onset, progressive course. This is in contrast to other types of genetic disorders that may have an earlier onset or a more variable pattern of inheritance.
**Correct Answer: D. Friedreich's ataxia**