Background: Several reports indicate that nocturnal production of melatonin is reduced in autism. Our objective was to examine whether melatonin production is decreased during the whole 24-h cycle, whether the melatonin circadian rhythm is inverted, and whether the reduction in melatonin production is related to the severity of autistic behavioral impairments.
Method: Day and nighttime urinary excretion of 6-sulphatoxymelatonin (6-SM) was examined during a 24-h period in post-pubertal individuals with autism (N=43) and typically developing controls (N=26) matched for age, sex and pubertal stage.
Results: Low 6-SM excretion (mean ± SEM) was observed in autism, both at daytime (0.16 ± 0.03 vs. 0.36 ± 0.05 μg/h, p<0.01), nighttime (0.52 ± 0.07 vs. 1.14 ± 0.23 μg/h, p<0.05), and during 24h (8.26 ± 1.27 vs. 18.00 ± 3.43 μg/24-h collection, p<0.001). Intra-individual nighttime-daytime differences (delta values) in 6-SM excretion were smaller in individuals with autism than in controls (0.36 ± 0.07 vs. 0.79 ± 0.23 μg/h, p<0.05). Nocturnal excretion of 6-SM was negatively correlated with autism severity in the overall level of verbal language (Spearman ρ=-0.30, p<0.05), imitative social play (Spearman ρ=-0.42, p<0.05), and repetitive use of objects (Spearman ρ=-0.36, p<0.05).
Conclusion: A deficit in melatonin production is present both at daytime and at nighttime in individuals with autism, particularly in the most severely affected individuals. These results highlight interest in potential therapeutic uses of melatonin in autistic disorder, especially in individuals with severe autistic impairment and/or low urinary 6-SM excretion.
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