Trinucleotide repeat disorder

Trinucleotide repeat disorder‏‎, also known as trinucleotide repeat expansion disorder or triplet repeat expansion disorder, is a set of genetic disorders caused by trinucleotide repeat expansion, a kind of mutation where trinucleotide sequences in certain genes exceed the normal, stable threshold, which differs per gene.

Overview

Trinucleotide repeat expansion is a mutation that results in the expansion of a sequence of three nucleotides, or a trinucleotide, in a gene. This expansion can lead to a variety of genetic disorders, collectively known as trinucleotide repeat disorders. The severity of these disorders often correlates with the length of the expanded repeat, with longer repeats generally leading to more severe symptoms.

Types of Trinucleotide Repeat Disorders

There are several types of trinucleotide repeat disorders, each caused by the expansion of a different trinucleotide sequence in a different gene. These include:

• Huntington's disease: Caused by the expansion of the CAG repeat in the HTT gene.
• Fragile X syndrome: Caused by the expansion of the CGG repeat in the FMR1 gene.
• Myotonic dystrophy: Caused by the expansion of the CTG repeat in the DMPK gene.
• Friedreich's ataxia: Caused by the expansion of the GAA repeat in the FXN gene.

Pathogenesis

The pathogenesis of trinucleotide repeat disorders is complex and not fully understood. However, it is known that the expanded trinucleotide repeat can interfere with the normal function of the affected gene, leading to a variety of symptoms. In some cases, the expanded repeat can lead to the production of a toxic protein that damages cells.

Diagnosis and Treatment

Diagnosis of trinucleotide repeat disorders typically involves genetic testing to identify the expanded trinucleotide repeat. Treatment is usually symptomatic, focusing on managing the symptoms of the disorder rather than curing the underlying genetic defect.

See Also

• Genetic disorder
• Mutation
• Nucleotide