LOW SERUM TRYPTOPHAN TO LARGE NEUTRAL AMINO-ACIDS RATIO IN IDIOPATHICINFANTILE-AUTISM

The serum tryptophan to large neutral amino acids ratio (Try/LNAA) is considered a reliable marker of tryptophan availability for brain sero tonin synthesis. A dysfunction of brain serotonergic activity has been postulated to exist in autistic disorder and supported by recent stud ies. On this basis, we determined the serum amino acids levels in 40 c hildren with idiopathic infantile autism as well as in 46 control chil dren. A significantly lower serum Try/LNAA ratio was observed in the a utistic subjects compared to the normal controls. In 14 autistic child ren (35%) this ratio was 2 SD below the mean value obtained in the con trol group. These results suggest that a low brain tryptophan avalaibi lity due to a low serum Try/LNAA ratio could be one of the possible me chanisms involved in the alteration of serotonergic function in autism .