Ring finger length and ALS Journal of Neurology, Neurosurgery and Psychiatry, May 2011

Having long ring fingers has been associated with a lethal nervous system disease known as amyotrophic lateral sclerosis (ALS). 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.

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. 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.

Researchers used a digital camera to photograph hands and finger length of 110 Britons, some with ALS and others without the disease. They 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 the most likely reason that men have longer ring fingers than index fingers, as compared to women.

The researchers found that 2D:4D ratio was lower for people suffering from ALS, compared with those without the disease. The relative lengths of the fingers provide a clue as to what makes the nerves vulnerable. It looks like male hormones in the womb not only make our nervous systems and muscles more masculine, they might also raise the risk of ALS.

However, the researchers stressed that the digit ratio has no use as a screening tool. What the study does find is that people with ALS tend to have more ‘male’ hands, with a ring finger relatively longer than the index finger - something that is a tendency in men. ALS is more common in men, but this might suggest that the reason is something to do with the balance of hormones one is exposed to in the womb, because finger length seems to be determined partly by the amount of male hormone a developing baby is exposed to.