A learning curve

"I have always been interested in the interplay of nature and nurture," says Professor Emily Simonoff of Guy’s, King’s and St Thomas’ Medical School. "My research on learning disabilities is prompted by the increasing evidence for genetic causes, plus the very strong evidence for environmental components. There have so far been no systematic studies of children with learning disabilities either in relation to the new genetic findings, or in relation to our greater understanding of the environmental factors. We hope to study both, and to learn more about the interplay between them."

In a new Wellcome Trust-funded study, Professor Simonoff and her team will be screening 6000 13- and 14-year-old children (years 8 and 9) from all secondary schools in Croydon in south London. The children will take paper-and-pencil aptitude tests (of the kind already used in many schools), and a selected group will have detailed medical examinations, including genetic testing, and cognitive profiling.

The aptitude tests are a reasonably good predictor of IQ, and will be used to identify children whose IQ scores are likely to fall in the range of 50-69. This is the accepted range for what is termed mild mental retardation (MMR). As Professor Simonoff points out, this terminology is quite contentious in the UK, as some regard it as pejorative: "It is the terminology used in the US, but in the UK the term ‘moderate learning disability’ is probably the closest. We have used MMR in this study because it is clearly defined by IQ, irrespective of cause, irrespective of behavioural problems, irrespective of social impairment. Terms will remain pejorative as long as we associate social stigma with a group of disadvantaged people."

The researchers will interview the parents of children falling in the lowest 5 per cent of scores, along with a control group. "Families have two effects on their children: they transmit genes and they form the environment of the child growing up. It’s very hard to separate these out. Early studies of MMR found it very hard to disentangle whether effects were to do with the lower ability of parents that was genetically transmitted, or to do with the environment parents who are socially disadvantaged can provide for their children."

The parental interviews will aim to separate the independent contribution of parental learning ability, as opposed to what is transmitted by other environmental measures such as socioeconomic status and chronic adversity. The involvement the parents have in their child’s cognitive development will be assessed by a series of specific questions, for example, how their child would get information for a school project, what involvement the parents would have with schoolwork, and how often.

On the genetic side, recent research has shown that the most common heritable form of MMR is likely to be fragile X syndrome, a chromosomal disorder associated with a fragile site on the X chromosome. (Down’s syndrome is the most common genetic cause, but is generally a newly occurring abnormality, not an inherited one.) "Fragile X is terribly important," explains Professor Simonoff. "It occurs in one in 4000-5000 males, and fewer females. It used to be thought that 'pathological causes' - such as genetic disorders or severe obstetric complications - gave rise to severe mental retardation, whereas mild mental retardation was due to sociocultural influences. In fact, if you look at children with fragile X, something like 60 per cent may have IQs in the MMR range."

There are a wide range of other genetic abonormalities, each less common than fragile X but collectively responsible for the majority of cases of severe learning disability. It will be important to find out how significant these are in MMR. According to Professor Simonoff, there are two alternative hypotheses behind the research: "One is that the individuals who have a genetic predisposition to MMR will be quite distinct from those with an environmental propensity. So there will be a genetic subgroup cutting across parental background, social class and childhood experience. Then there would be another subgroup who are primarily 'environmentally induced'. They will be a group in which there is greater parental learning disability, and greater social disadvantage. The alternative hypothesis is that a genetic predisposition and environmental risk leads to an increasingly greater risk of MMR. We really want to see if these two causes are independent or additive."

The aim of the study is to understand better the causes of mental retardation so that interventions can be targeted more effectively. For example, if genetic and environmental risk both increase the chances of having a learning problem, then lowering environmental risk will reduce learning problems, regardless of whether there are underlying medical risk factors. The study is also exploring the link between learning and mental health problems, as up to 30 per cent of children with learning disability are emotionally or behaviourally disturbed. This research will help to determine whether some groups of children with MMR are more likely to develop mental health problems; this could in the future lead to earlier intervention.

The study is taking place in Croydon because the borough is broadly representative of the UK. Moreover, says Professor Simonoff, "Not every borough could be as helpful as the Education Authority and individual schools in Croydon, who make all the difference to the success of the study."

Autism on the increase

Professor Simonoff is also involved in a Trust-funded project with Gillian Baird on the prevalence of autism in children. Autism is a behaviourally defined life-long developmental disorder of brain function. The main features are impairments in the child’s social interaction, a deficit in ‘social knowing’, language and play, with restricted and often repetitive interests and behaviours, unusual mannerisms, and either abnormally heightened or reduced sensory responses.

However, these features, as Dr Baird points out, may be manifest in very different ways. "You might have one autistic child who has no language, and another autistic child who talks a great deal but doesn't understand the rules of conversations. Or one child with an extensive fantasy world and another child with no pretend play at all." There is some overlap with general learning difficulty (MMR). "It is generally accepted that most autism is associated with an additional learning problem and that children with severe learning difficulties have a higher likelihood of some features of autism," says Dr Baird, "but you can find autistic behavioural features across a wide range of intellectual ability."

Dr Baird is a paediatrician who became interested in childhood neurodisability after working with children with a wide range of disabilities, including cerebral palsy, deafness and blindness. She was also, she says, extremely fortunate to spend time working with Dr Lorna Wing. "She was a clinical leader in identifying the core clinical features and later, in her work in Camberwell in the 1970s and 1980s, in formulating the spectrum of autism, which current genetic studies have in many ways confirmed."

Autism is being diagnosed more and more. "Everyone is noticing an apparent increase, community medical services, preschool placements, playgroups. What we don’t know is why. Are there more children with autism, are we better at recognising it, or has the diagnostic threshold changed?"

Dr Baird and colleagues have returned to a cohort of 40 000 children in the South Thames region, 16 000 of whom they first examined in the early 1990s. "We had developed a screening test for autism that would enable the early signs to be detected at 18 months. Most parents say that looking back they first began to notice something 'different' at that age. The screening test, developed by Simon Baron-Cohen, was used on 18-month-olds with an already diagnosed autistic older sibling and then in a population study as part of routine health surveillance."

Child health service records for the same South Thames region show 58 children per 10 000 have a diagnosis of autism. This is much higher than the generally accepted prevalence of 16 in 10 000, and higher than the number detected by the test. "Our screening was partially successful," explains Dr Baird, "because nearly all the children we picked up in that test did go on to develop autism. However, we missed a large number of children too; the test turned out to be specific, but not sensitive. We felt it essential at this stage to seek funding to enable us to see every child now diagnosed locally with an autistic spectrum disorder, using what would be regarded as the gold-standard research assessments, including developmental histories, current histories, and a videotaped observation of play and interaction to establish a research diagnosis. We will also use a panel of experts from the US, UK and Denmark to look at a selection of cases to see if they agree with our diagnoses, and try and obtain a consensus."

The main aim of the study is to be certain of the prevalence of autism. This clearly has profound implications for the planning of health and education services for this group of children. The reasons for any true increase would, however, need further study.

"We are clearly better at picking up the subtler varieties of autism," says Professor Simonoff, "and it may be that this increase is due to a threshold change. But there is also a lurking suspicion that there may be an actual increase in autism. The point is that we don’t know, and can't begin to look at this until we can be completely sure of the prevalence. Dr Baird's study, using the gold-standard diagnostic criteria, will enable us to do that."

External links

• Department of Child and Adolescent Psychiatry at the Institute of Psychiatry
• Autism99 Information Centre: Includes a paper published by Dr Gillian Baird
• National Autistic Society: Information about autism and Asperger syndrome
• Dr Lorna Wing: Articles published online
• Autism Research Centre at the University of Cambridge. Research interests and publications of Dr Simon Baron-Cohen

Further reading

Simonoff E, Bolton P, Rutter M (1996). Genetic influences in mental retardation. Journal of Child Psychology and Psychiatry. 37: 259-280.