Scientists have recently found something astonishing about Huntington’s disease, a serious brain disorder passed down through families. They’ve known about the genetic mutation that causes it for a while, but they weren't sure why people with the mutation don't have symptoms until they’re older.

It turns out, this mutation is silent for years. It grows slowly over time until it hits a certain point, then it starts making harmful proteins that kill brain cells. This happens when the mutation reaches a particular length.

Dr. Mark Mehler, who wasn’t part of the research, said this finding is a big deal. It helps solve some puzzles that scientists have been working on for a long time.

When brain cells die, people start having trouble moving, thinking, and acting normally. Symptoms usually start showing between 30 and 50 years old and get worse over time.

Scientists from different places like the Broad Institute, McLean Hospital, and Harvard Medical School studied brain tissue from 53 people with Huntington’s and 50 without it. They looked at half a million cells!

The key mutation has a repetitive sequence of DNA called CAG. In healthy people, this sequence repeats 15 to 35 times. But in people with Huntington’s, it repeats at least 40 times. Over time, this sequence gets longer and longer until it reaches about 150 repeats. That’s when certain brain cells get sick and die.

The researchers were surprised by their discovery. They found that these repeats grow slowly at first, but speed up after reaching 80 CAGs. The more repeats, the earlier symptoms start.

Some scientists didn't believe the findings at first. But the study showed that when the repeats reach at least 150, the disease starts. Previous work said 30 to 100 repeats weren't enough, but this new study shows they are when they reach 150.

This new understanding might help scientists find ways to delay or even prevent Huntington’s. Right now, there are medications to help with symptoms, but no cure. Some experimental drugs tried to lower the harmful protein, but they struggled because not many cells have it at once.

Maybe stopping the DNA repeats from growing would be a better way to fight the disease. There’s no guarantee this would work, but many companies are looking into it.

Unlocking Huntington’s Mystery: A Slow Build to Tragedy

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