Bulletin

Issue: September 2004

Research in Action

Searching for biological markers of autism

A multidisciplinary research group at La Trobe University has made a major contribution in the search for biological markers in autism spectrum disorders.

Developmental psychologist, Dr Cheryl Dissanayake, medical geneticist, Dr Danuta Loesch, and statisticians, Dr Richard Huggins and Dr Quang Bui, have discovered that children within the autism spectrum have faster physical growth rates during their first three years of life.

Recent publications on enlarged head circumference and brain size in children with autism aged between two and four years stimulated the interest of Drs Dissanayake and Loesch. These findings were outlined at the inaugural World Autism Congress in Melbourne in 2002 by American autism authority, Professor Eric Courchesne of the University of California at San Diego.

Dr Loesch is a world authority on the effects of the genetic abnormality on physical, cognitive, and behavioural measures in Fragile X disorder, the commonest form of inherited mental retardation.

She was intrigued by a similarity of Professor Courchesne's findings on the pattern of brain growth of children with autism with her own published data on body growth in children around the age of puberty with Fragile X syndrome. However, there had been no comparable studies of growth in children with autism.

Drs Dissanayake and Loesch undertook such a study in a pilot sample of young children using standard physical measurements collected by maternal and child health nurses as routine developmental check-ups between birth and three years - the period during which behavioural features which characterise autism become evident.

'We obtained infant and early childhood measurements of head circumference and stature of 16 children with high functioning autism and 12 children with the form of autism spectrum disorder defined as Asperger's Disorder - plus 19 normally developing children as a control group - to investigate whether growth abnormality in these groups is limited to the head and brain or may be more generalised,' Dr Dissanayake said.

The statisticians, Drs Huggins and Bui, used a 'linear mixed effects approach' to model growth over the three years. They found that growth rates in both head circumference and body height were elevated in the two clinical groups relative to the typically developing children, particularly between two to three years of age. However, the growth rates of the children with high functioning autism and Asperger's Disorder were identical.

One conclusion was that, because of similarities in growth of head circumference and body height and similarities in their behaviour, Asperger's Disorder was unlikely to be a discrete diagnostic entity, separate from Autistic Disorder.

Dr Loesch: 'The most exciting finding however, albeit preliminary, is that in autism, abnormal growth is not limited to the brain but may involve other body systems, highlighting the possibility that autism is associated with generalised growth dysregulation. Generally this finding strongly supports the role of biological mechanisms in the development of autism.'

Dr Dissanayake said the group now wanted to replicate these findings, and extend them by investigating growth during pre-adolescence and adolescence.

'This is a critical growth period, and we have recently applied for major funding to conduct this study. If our results are confirmed by replication on a larger scale, we can then start to look at the mechanisms that control growth and attempt to ascertain which candidate genes may be involved, enabling us to discover which biochemical and genetic mechanisms may be associated with autism.' •

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