Table 1.

Melatonin level assessment in the group of patients with autism spectrum disorder (ASD).

References	Number of Patients	Material	Results
Nir I et al., 1995 [49]	10 patients with ASD 5 controls	serum	1. Similar results of mean daily melatonin levels were measured in serum in the group of patients with ASD and the control group. 2. Patients with ASD showed lower melatonin levels at night and higher during the day relative to the control group.
Tordjman S et al., 2005 [47]	49 patients with ASD 88 controls	urine	1. Low melatonin levels were observed in 63% (31/49) of patients with ASD. 2. In pre-pubertal period, a reduction in 6-SM was apparently observed in patients with ASD relative to the control group.
Melke J et al., 2008 [37]	43 patients with ASD 34 parents 48 controls	plasma	1. Low melatonin levels were observed in 65% of patients with ASD. 2. There is a genetic potential for reduced melatonin levels in ASD, as asymptomatic parents also have abnormally low melatonin levels. 3. The results suggest that in patients with ASD and low melatonin levels we can get sleep improvement through supplementation.
Tordjman S et al., 2012 [43]	43 patients with ASD 26 controls	urine	Patients with ASD showed lower levels of nocturnal 6-SM excretion in urine than those in the control group.
Pagan C et al., 2014 [41]	278 patients with ASD 129 unaffected siblings 377 parents 416 controls	plasma	Melatonin levels in patients with ASD and their relatives were significantly lower than in the control group.
Abdulamir HA et al., 2016 [50]	60 patients with ASD 26 controls	serum	1. Patients with ASD presented lower levels of melatonin than the control group. 2. A relationship has been demonstrated between the severity of autism and lower melatonin levels.
Benabou M et al., 2017 [51]	157 patients with ASD 100 unaffected siblings 264 parents	plasma	Phenotypic variation and changes in melatonin levels in patients with ASD and their families are the result of environmental and genetic factors.
Braam W et al., 2018 [11]	60 mothers of a child with ASD 15 controls	urine	1. Mothers of children with ASD had significantly lower levels of 6-SM in urine compared to the control group. 2. Mothers of children with ASD were older at the time of child birth compared to mothers of children without ASD.
Maruani A et al., 2019 [52]	78 patients with ASD 90 unaffected relatives 47 controls	plasma	1. Patients with ASD presented lower levels of melatonin than their relatives and people from the control group. 2. Lower levels of melatonin were observed in relatives of patients with ASD, however, the result was not statistically significant.