**Core Concept**
Trinucleotide repeat disorders are a group of genetic conditions caused by the expansion of three nucleotides (a, c, or g) repeated multiple times in a gene. These repeats can lead to problems with gene expression and protein function, resulting in various clinical manifestations.

**Why the Correct Answer is Right**
The expansion of trinucleotide repeats in the coding regions of genes can lead to the synthesis of abnormal proteins, which can cause cellular dysfunction and disease. Examples of trinucleotide repeat disorders that affect coding regions include Huntington's disease (CAG repeats in the Huntingtin gene) and Spinocerebellar ataxia (CAG repeats in various genes). In contrast, trinucleotide repeat disorders that affect non-coding regions, such as the promoter or intron, can lead to disruptions in gene expression without directly affecting the coding sequence.

**Why Each Wrong Option is Incorrect**
**Option A:** Not specified, but if it refers to a trinucleotide repeat disorder, it should be a condition affecting the coding region.
**Option B:** Not specified, but if it refers to a trinucleotide repeat disorder, it should be a condition affecting the coding region.
**Option C:** Not specified, but if it refers to a trinucleotide repeat disorder, it should be a condition affecting the coding region.
**Option D:** Not specified, but if it refers to a trinucleotide repeat disorder, it should be a condition affecting the non-coding region.

**Clinical Pearl / High-Yield Fact**
Trinucleotide repeat disorders can be inherited in an autosomal dominant pattern, meaning a single copy of the mutated gene is sufficient to cause the condition. This is in contrast to autosomal recessive disorders, which require two copies of the mutated gene to manifest.

**Correct Answer: D.**