MONDAY, May 9 (HealthDay News) -- Having long ring fingers has been associated with a lethal nervous system disease known as amyotrophic lateral sclerosis (ALS), British researchers report.

Researchers hasten to explain, however, that this does not mean people with long ring fingers will develop the disease -- or even that they are at higher risk for it.

"We have not done a study that shows the risk of subsequently getting ALS in people with long ring fingers," cautioned lead researcher Ammar Al-Chalabi, a professor of neurology and complex disease genetics and director of King's MND Care and Research Center at King's College London.

What the study does find, Al-Chalabi said, is that "people with ALS tend to have more 'male' hands in that the ring finger is relatively longer than the index finger -- something that is a tendency in men."

"We already know that ALS is commoner in men, but this might suggest that the reason is something to do with the balance of hormones we are exposed to in the womb, because finger length seems to be determined in part by the amount of male hormone a developing baby is exposed to," he added.

ALS, sometimes called Lou Gehrig's disease, is a rapidly moving disease that is always fatal. Although it tends to leave people's intelligence intact, it attacks nerve cells in the brain and spinal cord that control voluntary movement, causing progressive weakness and paralysis.

Most people with ALS die within three to five years, although about 10 percent live 10 years or longer with the disease, according to the U.S. National Institutes of Health. When muscles in the chest fail, patients cannot breathe without ventilation and most eventually die from respiratory failure.

The cause of ALS isn't known. Although it can run in families, it strikes at random, and there is no cure.

The report was published in the May 9 online edition of the Journal of Neurology, Neurosurgery and Psychiatry.

For the study, Al-Chalabi's team used a digital camera to photograph hands and finger length of 110 people, some with ALS and others without the disease.

The investigators then looked at the ratio of the length of each person's index finger to ring finger -- called the 2D:4D ratio. The ratio is calculated by dividing the length of the index finger of the right hand by the length of the ring finger.

A low ratio indicates the ring finger is relatively long compared with the index finger. Scientists believe that this finger-length ratio is a marker of high prenatal testosterone levels. It is most likely the reason that men have longer ring fingers than index fingers, while women don't, the researchers said.

The researchers found that 2D:4D ratio was lower for people suffering from ALS, compared with those without the disease.

"The relative lengths of our fingers provide a clue as to what makes motor nerves vulnerable," Al-Chalabi said. "It looks like male hormones in the womb not only make our nervous systems and muscles more masculine, they might also make them more at risk of ALS."

He and the other researchers stressed, however, that the digit ratio "has no use as a screening tool."

Commenting on the study, Dr. Michael Geoffrey Benatar, an associate professor of neurology at the University of Miami Miller School of Medicine, said that "the idea that some early event in life makes one's susceptibility to a neurodegenerative disease is not an unreasonable idea at all."

The context of this notion is that it is not known what puts people at risk for ALS, he said. Whether or not finger size is really connected to the risk of ALS remains to be seen, Benatar said.

"I don't think one can take finger measurements and say 'you're at risk or you are not at risk,' but the idea that this might represent a biological marker is an interesting observation and warrants further study," Benatar said.

More information

For more information on ALS, visit the U.S. National Institute of Neurological Disorders and Stroke.