What is CAG expansion?
Huntington disease (HD [MIM 143100]) is a dominantly inherited progressive neurodegenerative disorder that results from a mutation that expands the polymorphic trinucleotide (CAG) tract in HTT. The average control CAG tract size in the general population is 17–20 repeats.
What does CAG mean in DNA?
The HTT mutation that causes Huntington disease involves a DNA segment known as a CAG trinucleotide repeat . This segment is made up of a series of three DNA building blocks (cytosine, adenine, and guanine) that appear multiple times in a row. Normally, the CAG segment is repeated 10 to 35 times within the gene.
What is TNRE?
Trinucleotide repeat expansion, is a DNA mutation that is responsible for causing any type of disorder classified as a trinucleotide repeat disorder. These disorders are progressive and effect the sequences of the human genome, frequently within the nervous system.
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What is a trinucleotide?
Definition of trinucleotide : a nucleotide consisting of three mononucleotides in combination : codon.
Where is the CAG repeats?
The disease is caused by a CAG trinucleotide repeat expansion located in the first exon of the HD gene. The CAG repeat is highly polymorphic and varies from 6 to 37 repeats on chromosomes of unaffected individuals and from more than 30 to 180 repeats on chromosomes of HD patients.
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What is the CAG sequence?
The gene responsible for HD contains a sequence with several CAG repeats (Cytosine, Adenine, Guanine). We all have these CAG repeats in the gene that codes for the huntingtin protein, but people with HD have a greater number than usual of CAG repeats in one of the genes they inherited.
How many Trinucleotides are there?
Five different types of trinucleotide repeats are present in the transcripts of 16 genes known to be associated with TREDs. They include the (CUG)n, (CAG)n, (CGG)n, (CCG)n and (AAG)n repeats that occur either in translated or non-translated sequences (reviewed in 24–28).
Why do the repeats cause Huntington’s?
Huntington’s disease is caused by a mutation in the HD gene in which the same three bases? (CAG) are repeated many more times than normal. This is known as a CAG trinucleotide repeat expansion. In people who don’t have Huntington’s disease this section of CAG repeats in the gene is usually only repeated 10 to 35 times.
What is anticipation genetics?
Listen to pronunciation. (jeh-NEH-tik an-TIH-sih-PAY-shun) A phenomenon in which the signs and symptoms of some genetic conditions tend to become more severe and/or appear at an earlier age as the disorder is passed from one generation to the next.
What causes CAG repeat expansion?
Mechanism. Triplet expansion is caused by slippage during DNA replication or during DNA repair synthesis. Because the tandem repeats have identical sequence to one another, base pairing between two DNA strands can take place at multiple points along the sequence.
