A new blood test gives families carrying ALS genes something they’ve never had: a real warning and a chance to act before symptoms begin.

Imagine knowing you carry a gene that will almost certainly cause a devastating disease, but not knowing if it will happen next year or in twenty years. Actually, this is the case for several neurologic disorders, such as Alzheimer’s and Huntington’s chorea. And it is the reality for thousands of families who carry genetic mutations linked to amyotrophic lateral sclerosis, the disease better known as ALS or Lou Gehrig’s disease.

Not everyone wants to know if they carry the gene, but not knowing means you place yourself at risk of missing out on early treatments for these diseases or treatments that could slow the disease process down. Which is better: knowing or not knowing? Of course, the choice is yours, but you must carefully weigh the benefits of knowing against the stress of not knowing.

I once worked at a hospital where a young woman knew that Huntington’s ran in her family, and at that point she was showing symptoms of slight trembling, some problems with her memory and gait. I sometimes wonder what happened to her and if she was able to get any kind of treatment or into an early clinical trial. Did she ever get to complete her doctorate and go into practice as a psychologist? I’ll never know.

ALS destroys the nerve cells that control muscle movement, and most people live only two to five years after their first symptoms appear. For these families, the not knowing has often been almost as hard as the disease itself.

That may change now as new research is indicating there are ways to predict future development of ALS. A team of researchers, led by scientists at the University of Miami, has found a way to read the earliest warning signs of ALS in a simple blood draw, sometimes years before a person ever notices a twitch, a stumble, or a slur in their speech. It is one of the most hopeful developments in ALS research in years, and it points toward a future where doctors might step in before the disease ever takes hold.

This shift is part of something bigger happening across brain medicine. Alzheimer’s and Parkinson’s researchers are also racing to catch their…