Why does Huntington's Disease run in families?

THAT'S THE WHY: Huntington's disease is a cruel condition: cells die away in particular regions of the brain and the patient develops problems with movement, emotions and mental function.

Symptoms tend to show up around middle-age and then worsen. There is no cure.

The condition nearly always runs in families, and there’s a fairly straightforward reason why: the cause of the disease is a particular type of genetic mutation on chromosome 4.

If a copy of the mutated gene gets passed on to offspring, they too will develop the condition.

We all carry a stretch in that gene where the DNA “letters” CAG repeat several times, but in the Huntington’s mutation, there are too many CAG triplets.

Also, the initial mutation of extra CAGs that the person is born with seems to confuse some usually protective proteins in the brain cells, and even more CAG repeats get added on, explains Prof Robert Lahue from NUI Galway.

This further expansion of the mutation appears to be linked with how fast symptoms progress, he adds.

Lahue and colleagues at the Centre for Chromosome Biology have just identified an enzyme involved in this expansion process, and by interfering with the enzyme they were able to reduce expansions by about 75 per cent in cells in the lab. That study was funded by Science Foundation Ireland.

The discovery, published in PLoS Biology this month, is by no means a cure, notes Lahue, but it could point to new ways to slow the development of symptoms. The team now hopes to test the approach preclinically.