spatial tasks (Rutter 1978, 1983). Asperger syndrome is a neurobiological disorder that has many clinical symptoms in common with autism. Individuals exhibit decreased social awareness and ability to cope with change. They can often display obsessive and repeti- tive behaviour. The etiology of autism is unclear, but genetic factors are extremely important. Indeed, autism is one of the most strongly genetic of all child psychiatric disorders. Inheritability estimates of 91–93% for an underlying liability to autism have been estimated in several UK studies (Rutter et al., 1993). These au- thors also point out that in regard to siblings the rate is extremely high in relation to the rarity of autism in the general population, an increase in risk of some 50–100 times. Autistic behavior has been attributed to an abnor- mal functional imbalance among the neurotransmitter amines dopamine, noradrenaline, and serotonin. Cook (1990) stated in his review that neurochemistry in autism has been the most validated in childhood neu- ropsychiatric disorders. Of the neurotransmitters, hy- perserotonemia in particular shows a familial pattern and is found consistently in over 25% of children and adolescents with autism. Other research groups have INTRODUCTION Since the first reports describing childhood autism (Kanner 1943) there have been several attempts to find a common cause or biochemical marker among the many children that display symptoms of autism. In Kanner’s original study he observed that although the parents of autistic children on the whole appeared in- telligent, there were signs of obsessive behavior in the family background and the children were generally di- agnosed as schizophrenic (Kanner 1943). Autism is indeed a difficult disorder to characterize because the children often display differing clinical features. Com- mon factors, however, are defects in communication and socialization. Autistic children often perform poorly in tasks requiring sequential skill and concep- tualization but are more able to carry out nonverbal Plasma Amino Acid Levels in Children with Autism and Their Families Sarah Aldred, 1 Kieran M. Moore, 2 Michael Fitzgerald, 2 and Rosemary H. Waring 3 Plasma amino acid levels were measured in autistic and Asperger syndrome patients, their siblings, and parents. The results were compared with values from age-matched controls. Patients with autism or Asperger syndrome and their siblings and parents all had raised glutamic acid, phenylalanine, asparagine, tyrosine, alanine, and lysine ( p  .05) than controls, with reduced plasma glutamine. Other amino acids were at normal levels. These results show that children with autistic spectrum disorders come from a family background of dysregulated amino acid metabolism and provide further evidence for an underlying biochemical basis for the condition. KEY WORDS: Autism; Asperger syndrome; plasma; amino acids; glutamate/glutamine ratio. Journal of Autism and Developmental Disorders, Vol. 33, No. 1, February 2003 (© 2003) 93 0162-3257/03/0200-0093/0 © 2003 Plenum Publishing Corporation 1 Pharmaceutical Sciences Research Institute, Aston University, Birmingham, B4 7ET, United Kingdom. 2 Lucena Clinic, Child and Adolescent Mental Health Services, Bless- ington Rd, Tallaght, Dublin 24, Ireland. 3 School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT. United Kingdom; e-mail: R.H.Waring @bham.ac.uk