Which of the following is an example of Trinucleotide repeat mutation ?
**Core Concept**
Trinucleotide repeat mutations involve the expansion of repetitive DNA sequences consisting of three nucleotides, leading to genetic instability and various diseases. These expansions can occur in coding or non-coding regions and are associated with several neurodegenerative disorders. The mechanism of trinucleotide repeat expansion involves the formation of hairpin structures that facilitate the slippage of DNA polymerase, resulting in the amplification of the repeat sequence.
**Why the Correct Answer is Right**
Trinucleotide repeat expansions, such as CAG repeats, are found in genes like Huntingtin in Huntington's disease and Androgen Receptor in Spinobulbar muscular atrophy (Kennedy's disease). The expansion of these repeats leads to the formation of a toxic protein that causes cellular damage and neurodegeneration. The repeat expansion can also lead to epigenetic changes, such as DNA methylation and histone modification, which contribute to the disease phenotype. The CAG repeat expansion in Huntingtin is a classic example of trinucleotide repeat mutation.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify a trinucleotide repeat mutation. While it may involve a repetitive sequence, it is not a characteristic example of this type of mutation.
* **Option B:** This option is incorrect as it refers to a point mutation, which involves a single nucleotide change rather than a repetitive sequence expansion.
* **Option D:** This option is incorrect as it refers to a chromosomal deletion, which involves the loss of a segment of DNA rather than a repetitive sequence expansion.
**Clinical Pearl / High-Yield Fact**
Trinucleotide repeat expansions are associated with several neurodegenerative disorders, including Huntington's disease, Spinobulbar muscular atrophy (Kennedy's disease), and Fragile X syndrome. These disorders often present with progressive motor and cognitive decline, and early recognition and genetic testing can help with diagnosis and family planning.
**Correct Answer:** C.