Excretion of 6-hydroxymelatonin sulfate (6-OHMS) in siblings during childhood and adolescence.

The analysis was performed to support the assumption that in inter-individual variations melatonin production is determined genetically. Sixty-six siblings from 31 families (27 girls, 39 boys, 3-18 years) contributed to this study with 3 to 15 urine samples collected once a year over 24 h. The samples were stored at -20 degrees C and analyzed for the daily output of the melatonin metabolite 6-hydroxymelatonin sulfate (6-OHMS) by an enzyme-linked immunosorbent assay (ELISA). The results indicate that 6-OHMS excretion was significantly correlated in siblings (r = 0.37, p = 0.01), suggesting a possible genetic background of melatonin production. However, prospective studies controlling also lifestyle factors such as diet are required to further confirm the hypothesis.