Which of the following is NOT a trinucleotide repeat mutation disorder?

Sickle cell anemia is a genetic disorder caused by a single point mutation in the HBB gene, which encodes the beta-globin subunit of hemoglobin. This specific mutation results in the substitution of valine for glutamic acid at the sixth position of the beta-globin chain, leading to the formation of abnormal hemoglobin S. Unlike disorders caused by trinucleotide repeat expansions, sickle cell anemia does not involve the repetition of nucleotide segments.

In contrast, Huntington's disease is associated with an expansion of CAG repeats in the HTT gene, Fragile X syndrome involves an expansion of CGG repeats in the FMR1 gene, and myotonic dystrophy is characterized by CTG repeats in the DMPK gene. Each of these disorders is linked to the instability of repeating sequences that can expand in successive generations, leading to the clinical features observed in affected individuals. Thus, sickle cell anemia stands out as it does not fall into the category of trinucleotide repeat mutation disorders.