Which term describes a family of autosomal dominant diseases caused by insertion of multiple copies of a 3-base pair sequence (CAG) that codes for the amino acid glutamine?

Which term describes a family of autosomal dominant diseases caused by insertion of multiple copies of a 3-base pair sequence (CAG) that codes for the amino acid glutamine?

• A. Trinucleotide repeat diseases
• B. Point mutation
• C. Autosomal dominant disease
• D. X-linked disorders

Answer: (A)

Trinucleotide repeat diseases are defined by expansions of a three-base-pair sequence in certain genes. In this case, the repeat is CAG, which codes for the amino acid glutamine. When these repeats expand beyond a normal threshold, the protein gains long polyglutamine tracts that disrupt function and lead to neurodegeneration. These disorders are typically inherited in an autosomal dominant pattern and often show anticipation, where symptoms appear earlier or worsen in successive generations due to increasing repeat length. Huntington disease is a classic example, caused by expanded CAG repeats in the HTT gene, illustrating how the same mechanism underlies a family of related conditions. The description does not fit a single base-pair point mutation, a broad autosomal dominant category, or X-linked inheritance, making trinucleotide repeat expansion the best match for this scenario.

Trinucleotide repeat diseases are defined by expansions of a three-base-pair sequence in certain genes. In this case, the repeat is CAG, which codes for the amino acid glutamine. When these repeats expand beyond a normal threshold, the protein gains long polyglutamine tracts that disrupt function and lead to neurodegeneration. These disorders are typically inherited in an autosomal dominant pattern and often show anticipation, where symptoms appear earlier or worsen in successive generations due to increasing repeat length. Huntington disease is a classic example, caused by expanded CAG repeats in the HTT gene, illustrating how the same mechanism underlies a family of related conditions. The description does not fit a single base-pair point mutation, a broad autosomal dominant category, or X-linked inheritance, making trinucleotide repeat expansion the best match for this scenario.