Genetic research teams around the world are hunting for the "gene for language" after scientists have found powerful evidence for an instinct for grasping language - and an inherited disorder that impedes it.

Scientists have been searching for evidence that there is an innate disposition to develop language, building on discoveries such as the finding that children all over the world pick up the complexities of their language at the same age. Linguists have shown that all languages have the same elements of structure.

Myrna Gopnik, professor of linguistics at McGill University, Montreal, Canada, has studied people suffering from a disorder in which they make basic errors in forming sentences in their native languages. "Though most children acquire language quickly and easily, some children have great difficulty," she said. The disorder aggregates in families: this fact, and studies of twins, point to a genetic factor. Professor Gopnik thinks that sufferers have to learn parts of their native language in a laborious, rule-following way rather than instinctively, as she says most of us do.

By giving sufferers novel words and asking them to change the tense or the case, she has shown that they are not following the normal methods of language construction. Instead, they compensate by memorising tenses and cases and by explicitly learning rules of grammar. For example, they might change "walk", correctly, to "walked" - but they would then change "go" to "goed".

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"The impaired have serious problems in inflecting novel forms," she said at a conference, the Evolution of Social Behaviour Patterns in Primates and Man, held in London this week.

Now Professor Gopnik is getting similar results from experiments in Japanese, with verbs and nouns, and Greek, with pluralisation.

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She says that the results cannot be explained by problems in articulation, auditory problems or differences in intelligence levels.

"The results show that there is a genetic component to language," she said. "These data suggest that this genetic disorder directly affects normal language learning mechanism.

"Our best guess is that it affects the establishment of the neurological structure."