New Delhi, July 3 -- SAN DIEGO - For thirty thousand Americans carrying a genetic defect in a single gene, Huntington's disease has been a one-way street. The mutation accumulates silently through childhood and early adulthood, then starts dismantling movement, memory, and personality with a precision that no approved therapy has yet been able to interrupt.

A study published Wednesday in Nature offers an early indication that one key part of that dismantling process can, at least in mice, be reversed. Researchers at the University of California San Diego, working with collaborators at the Max Planck Institute for Biological Intelligence in Germany, identified a population of brain cells whose activity collapses early in Huntington's dise...