Trinucleotide repeat expansion

Diagram illustrating trinucleotide repeat expansion.

Trinucleotide repeat expansion is a genetic phenomenon where certain sequences of three nucleotides (trinucleotides) are repeated more times than normal in the genome. This expansion can lead to various genetic disorders, depending on the location and extent of the repeat.

Mechanism

Trinucleotide repeats are sequences in the DNA where a series of three nucleotides is repeated multiple times. These repeats can be found in various parts of the genome, including coding and non-coding regions. During DNA replication, these repeats can become unstable and expand due to slippage of the DNA polymerase. This slippage can cause the newly synthesized strand to misalign with the template strand, leading to an increase in the number of repeats.

Associated Disorders

Trinucleotide repeat expansions are associated with several genetic disorders, often referred to as trinucleotide repeat disorders. These disorders are typically characterized by neurological symptoms and can vary in severity. Some well-known disorders include:

• Huntington's disease
• Fragile X syndrome
• Myotonic dystrophy

The severity and onset of these disorders often correlate with the number of repeats; larger expansions tend to result in more severe symptoms and earlier onset.

Genetic Anticipation

A notable feature of trinucleotide repeat disorders is genetic anticipation, where the symptoms of a genetic disorder become more severe or appear at an earlier age as the disorder is passed on to the next generation. This is due to the tendency of the repeat expansions to increase in size when transmitted from parent to offspring.

Diagnosis and Testing

Diagnosis of trinucleotide repeat expansion disorders typically involves genetic testing to determine the number of repeats in the relevant gene. Techniques such as polymerase chain reaction (PCR) and Southern blotting are commonly used to assess repeat length.

Treatment and Management

Currently, there is no cure for trinucleotide repeat expansion disorders, but various treatments can help manage symptoms. These may include medications to control neurological symptoms, physical therapy, and supportive care. Research is ongoing to find potential therapies that target the underlying genetic causes.

Related Pages

• Genetic disorder
• DNA replication
• Genetic testing