CAG Trinucleotide Repeat ∞ Area

CAG Trinucleotide Repeat

Meaning

A CAG trinucleotide repeat refers to a specific DNA sequence, cytosine-adenine-guanine, repeated multiple times within a gene. These segments are common in the human genome. When their number expands beyond a stable threshold, it becomes associated with various genetic disorders by influencing protein function.

Context

CAG trinucleotide repeats reside within the coding regions of specific human genes. Their stability is crucial for accurate gene transcription and translation into functional proteins. The precise length maintains gene integrity and proper cellular function; variations influence protein structure and activity.

Significance

Abnormal expansion of CAG trinucleotide repeats holds substantial clinical significance as the cause of inherited neurodegenerative conditions like Huntington’s disease and spinocerebellar ataxias. Repeat numbers correlate with disease onset age and symptom severity, providing essential diagnostic and prognostic information for clinical management.

Mechanism

Excessive CAG repeat expansion within a gene’s coding region translates into an abnormally long polyglutamine tract. This extended segment causes the protein to misfold, aggregate, and accumulate within specific neurons. This toxic gain-of-function disrupts cellular processes, leading to neuronal dysfunction and cell death, manifesting neurological symptoms.

Application

Genetic testing for CAG trinucleotide repeat expansions is a standard diagnostic tool for individuals with symptoms of polyglutamine diseases. It is used in presymptomatic testing for at-risk family members, offering critical information for reproductive planning. Research focuses on developing therapies targeting expanded repeats or their toxic products.

Metric

The primary metric is the number of CAG repeats, determined through molecular genetic techniques like PCR and fragment analysis or sequencing. The precise count provides a quantitative measure linked to disease risk and phenotype. Clinical assessment of neurological symptoms and functional decline aids in monitoring disease progression.

Risk

The primary risk associated with expanded CAG trinucleotide repeats is the development of severe, progressive neurodegenerative disorders, for which no cures exist. Genetic testing carries psychological risks, including anxiety, depression, and distress for presymptomatic individuals receiving a positive result. Inadequate genetic counseling can lead to significant patient distress.

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HRTioJuly 19, 2025