A review of studies on the body fluid levels of neuroactive amino acids, including glutamate, glutamine, taurine, gamma-aminobutyric acid (GABA), glycine, tryptophan, d-serine, and others, in autism spectrum disorders (ASD) is given. The results reported in the literature are generally inconclusive and contradictory, but there has been considerable variation among the previous studies in terms of factors such as age, gender, number of subjects, intelligence quotient, and psychoactive medication being taken. Future studies should include simultaneous analyses of a large number of amino acids [including d-serine and branched-chain amino acids (BCAAs)] and standardization of the factors mentioned above. It may also be appropriate to use saliva sampling to detect amino acids in ASD patients in the future—this is noninvasive testing that can be done easily more frequently than other sampling, thus providing more dynamic monitoring.

Neuroactive steroids (rapidly acting steroids that act as allosteric modulators of neurotransmitter receptors such as the ɣ-aminobutyric acid A (GABA A ) receptor and the NMDA glutamate receptor) are involved in brain development and have been proposed to be important in the etiology and/or pharmacotherapy of a number of psychiatric and neurologic disorders, but there is limited information available on their association with autism spectrum disorders (ASD). This paper reviews the possible involvement of neuroactive steroids (NASs) and some related steroids, including testosterone, androstenedione and estradiol steroids in the etiology of ASD. NASs include progesterone, pregnanolone, pregnenolone, pregnenolone sulfate, allopregnanolone, tetrahydrodeoxycorticosterone (THDOC), dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS). Studies on the levels of NASs and related steroids in blood, urine, saliva, and amniotic fluid in ASD are also reviewed. The results on plasma levels of NASs in ASD reported in the literature are generally inconclusive, probably because of differences among studies in terms of experimental design and factors such as age, gender, number of subjects, and medication being taken and differences in time of day at which samples are taken and storage conditions of samples. Future studies on levels of NASs in ASD should include careful consideration of the factors mentioned above, the possible advantages of saliva sampling and the use of assay procedures that provide simultaneous analysis of levels of a large number of these steroids.