(PARIS-AFP) - Scientists said on Tuesday they had identified a gene that appears to play an important part in babies' language development.

A telltale stretch of DNA at a gene called ROBO2 is linked to the number of words that a child masters in the early stage of talking, they reported in the journal Nature Communications.

ROBO2 controls a protein that directs chemicals in brain cells that may be used for developing language and producing sounds.

The gene lies on a region of Chromosome 3 which has previously been implicated in dyslexia and speech-related disorders, according to the study.

ROBO2's protein also interacts with cousins in the ROBO group of proteins that have been linked to problems with reading and remembering speech sounds.

Infants generally start to form and produce words at about the age of 10 to 15 months.

From 15 to 18 months, English-speaking infants go through a development spurt to reach a vocabulary of about 50 words.

From 18 to 30 months, this widens to about 200 words, which they start putting together into more complex grammatical structures.

By the age of six, some 14,000 words have been mastered, and by the time a child leaves high school, the tally is usually about 50,000.

The results build on previous research in 1997 and 1998 among two-year-olds that found language development is influenced -- but only modestly -- by genes.

ROBO2 appears to be specific to the early development stage of one-word communication.

More work is needed to uncover how its functions are affected by other DNA variations nearby, and what the implications may be for learning. Another task is to see whether another gene or genes also play a part in language acquisition.

The investigation, led by epidemiologists at the University of Bristol in western England, drew on a genetic comparison of nearly 11,000 toddlers of European descent whose learning progress, from the one-word to the two-word stage, had been monitored.

"The research helps us to understand the genetic factors which may be involved in the early language development in children, particularly at a time when children speak with single words only," said Beate St. Pourcain, at the university's Integrative Epidemiology Unit.

It "strengthens the link between ROBO proteins and a variety of linguistic skills in humans."