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May 26, 2004
CAG Counts - Why Is 40 A Problem?
There are a number of diseases that are a result of too many repeats in a DNA sequence. For Huntington's Disease it tends to be 40+ CAG repeats in one specific spot.
Recently, it's been theorized that this is due to the replication process becoming 'stuck', kind of like a skip on a record album. (If you're under 35, ask your parents what that means.) This causes the number of repeats to expand over time.
Researchers studying Friedreich's Ataxia, another disease involving 40+ repeats in a DNA sequence, found that the longer strands of repeats caused the DNA to become three-stranded instead of the 'normal' double-helix formation. Somehow this causes the replication process to get stuck in a loop.
It wouldn't be a bit surprising if this HD gene also resulted of the three-stranded formation. You can read an article on this here (from the Chicago Sun-Times.)
Posted by Dave at May 26, 2004 05:46 AM
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