By Philip Cohen
 

For the first time, scientists are hot on the trail of a gene that shapes the development of human language. The discovery may help explain why many speech and language disorders arise.

Scientists know that our genetic heritage can strongly affect our ability to communicate. For example, identical twins tend to share linguistic ability or disability.

Geneticists have tried to hunt down the genes that influence language abilities by studying language disorders that can be inherited, such as stuttering. But such disorders tend to have complex patterns of inheritance, suggesting that many genes are involved, each making a small contribution. And so far, they have not snared a single solid candidate.

But now British researchers say they are close to identifying a gene they call SPCH1. They report that after only six months of work, they have narrowed their search to a small section of human chromosome 7 (Nature Genetics, vol 18, p 168). "This is a very good place to land," says geneticist Anthony Monaco of the University of Oxford. "It's a well-mapped area, so the rest of our work should go quickly."

The advance has only been possible because of an unusual family scientists refer to as KE. Ten years ago, members of this family arrived at the Institute of Child Health in London complaining that some of their relatives had a strange speech affliction. "What strikes you first is that their speech is unintelligible," says Faraneh Vargha-Khadem, a neuropsychologist at the institute.

The afflicted relatives proved to have deficits in all aspects of speech, and difficulty coordinating some facial muscles required for speech. Afflicted children also had trouble mastering reading and writing. But what truly singled out the KE disorder was the simple pattern of its inheritance. Genetic analysis revealed that the condition was caused by a single, dominant mutation that could be traced back to one of their grandmothers.

Vargha-Khadem and her colleagues collaborated with Monaco's team to locate the defective gene. They analysed different chromosome segments, reasoning that afflicted individuals should share the grandmother's version of the regions. Two closely spaced segments of chromosome 7 showed a perfect match: they were present in 15 linguistically impaired relatives, but absent in 12 healthy ones.

This means that SPCH1 has to lie very close by, says Monaco. His team also notes in research yet to be published that the same region on chromosome 7 also plays a part in autism, another condition where language is impaired. "This suggests we are going to be helped a lot by knowing how this gene works, and what role it plays in other disorders," says Vargha-Khadem.

"It's exciting to think we're going to start studying something as incredibly sophisticated as language gene by gene," says Dennis Drayna of the National Institute on Deafness and other Communication Disorders near Washington DC. "This paper is a small step, but it has big implications."