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Pointing the Finger

A child's future really may be written in his hands

A child's future really may be written in his hands - not in the creases of his palms but in the relative lengths of his fingers. A report just published in Developmental Medicine and Child Neurology suggests that people with autism have ring fingers that are abnormally long compared with their index fingers.

Children with autism have trouble interacting with other people. Both their verbal and their gesture-based communication is poor, and they often have low intelligence. Early hallmarks - a failure to point at things, follow the gaze of someone else, or engage in pretend play - are often obvious by the tender age of 18 months. About one child in 500 suffers from the condition.

John Manning, a researcher at the University of Liverpool, in Britain, who has studied what fingers can indicate about everything from fertility to sexual preference, teamed up with Simon Baron-Cohen at the University of Cambridge, whose expertise is in autism. They studied 72 autistic children and 23 with Asperger's syndrome, a related condition in which the individual's intelligence is not affected.

Dr Manning and Dr Baron-Cohen photocopied the children's hands, and carefully measured the lengths of their subjects' fingers from the copies. They worked out the ratio of the length of the index finger to the length of the ring finger for each child, and compared it with those of 34 of the children's healthy siblings, 88 of their fathers, 88 of their mothers, and a number of unrelated controls that were matched for sex and age.

The relative sizes of someone's fingers are fixed for life within three months of conception, and the relationship seems to be governed by testosterone. Although the reason is not yet understood, earlier studies have shown that finger-length ratios are a robust marker of how much of that hormone a baby has been exposed to in utero - the more testosterone, the longer the ring finger. Overall, therefore, men tend to have longer ring fingers than index fingers, whereas in women the two fingers are more likely to be of equal length.

Dr Manning and Dr Baron-Cohen found that autistic children had extremely long ring fingers compared with their index fingers. Children with Asperger's also had abnormal index-to-ring finger ratios, though less so than full-blown autistics. Even the unaffected siblings and parents of the autistic children had ratios that differed significantly from the normal controls.

That may sound surprising, but high levels of testosterone in the womb have been linked to several other brain-related phenomena, including left-handedness, dyslexia and female homosexuality. Dr Manning thinks that the families of autistic children are genetically predisposed to produce high levels of testosterone during early development. (The fetus makes most of the testosterone itself. In males, it comes from the testes and adrenal glands; in females from the adrenals alone. Only a small amount, if any, comes from the mother.)

While high levels of testosterone may not solve the whole puzzle of autism, Dr Manning thinks levels in utero may be an important piece of it. The finding bolsters what is known as the "extreme male brain" theory of autism. As the name suggests, autism - which is, in any case, much more common in men than women - may simply be an extreme magnification of traits, such as problems with communication and empathy, that psychological testing has shown (to the surprise of few women) are more frequently found in men.

Source: The Economist 24 March 2001

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