Speak out!

Researchers identify a gene linked to speech problems

 
Published: Wednesday 31 October 2001

  Correcting gene mutation cou researchers have recently discovered a gene which when it mutates causes speech breakdown. The gene switches other genes on and off and, therefore, could show the way for understanding the genetic network of language learning and use. The gene, called foxp 2, was identified by a team of researchers from the University of Oxford in the uk .

This genetic find emerged while researchers were studying several members of a British family who had a severe speech and language disorder. In the so-called ke family, 15 of the 37 members across four generations had low verbal and spatial intelligence, difficulties in pronouncing a wide range of sounds and grammatical deficits such as failing to grasp rules for forming the past tense of verbs. "The affected members of the ke family display a substitution of a single nucleotide in one of their two copies of the foxp 2 gene. This is the reason behind all their problems," says study co-author Faraneh Vargha-Khadem, a neuroscientist at the Institute of Child Health in London.

The team had been studying the ke family for several years. By 1998, they had ascertained that its problems were due to mutation in a gene of chromosome 7. Data from the human genome project suggested that there were about 70 genes in the chromosome. "For a long time, we kept marching down the chromosome using genetic markers to narrow down the gene, but could not make much progress," says Cecilia S L Lai, a geneticist at the Oxford University and the lead author of the study.

They made a breakthrough after a boy with similar difficulties turned up. Comparing the two, the team was able to identify the gene since it was also mutated in the boy termed as ' cs patient'. "It probably saved us a year or two," says Simon Fisher, another member of the Oxford team. Studying both the cs patient and the ke family, the researchers found that the foxp 2 gene produces a protein called a transcription factor, which attaches itself to other regions of dna and switches genes on and off. In the ke family, one of 2,500 units of dna that make up the foxp 2 gene is mutated. This mutation prevents foxp 2 from activating the normal sequence of genes required for early brain development. "It is extraordinary that such a minute change in the gene is sufficient to disrupt a faculty as vital as language," said Anthony Monaco of the Oxford University who led the genetic aspects of the study.

Although humans have two copies of every gene, just one mutated copy of foxp 2 -- as in the case of both cs and the ke family -- can have devastating effects on brain development, opines Vargha-Khadem. Brain imaging studies of the ke family revealed that affected members have abnormal basal ganglia -- a region in the brain involved with movement. This could be the reason for them having difficulty in moving their lips and tongue. Regions of the cortex involved in speech and language were also found to be aberrant. The researchers attributed such problems to the fact that the gene is required in early development of an embryo to ensure the formation of brain regions involved in speech and language functions.

The discovery of foxp 2 offers geneticists a chance to look for other genes involved in development, especially those directly controlled by foxp 2. "It's an unbelievably complex system and we have got one tiny glimpse," says Michael Tomasello, a psychologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Even psychologist Karin Stromswold of Rutgers University in New Jersey agrees with him. He says that foxp 2 is an important piece of the genetic puzzle of language. "The finding provides a smoking gun for a genetic cause of one kind of language disorder," contends psychologist Steven Pinker of the Massachusetts Institute of Technology, usa .

However, the gene's specific influences on brain development remain unknown, Vargha-Khadem says. "It is important to realise that this is not the only gene associated with the capability to speak," said Monaco. He added that foxp 2 is unlikely to be the cause of less severe language deficits that affect approximately four per cent of schoolchildren. Some experts say that the finding won't resolve the decades-long debate about genes mapping out grammar circuits in the brain or participating in a more general developmental process underlying language use.

The controversy still smoulders over whether the ke 's symptoms have more to do with their inability to control their mouths or some general brain problem. Supporters of a more purely linguistic interpretation of the family's difficulties point out that the ke 's intelligent quotient, although below average, is within the normal range. Stromswold cautions that foxp 2's "very messy" effects necessitate further studies of families with more limited impairments. Monaco's team is currently scanning the genomes of such families. foxp2 is not unique to humans -- it is also found in animals. A collaborative project is in progress to study the evolution of the human foxp 2 gene by comparing it with versions in chimps and other primates.

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