In this study we investigated the relationship between melatonin pathway and multiple sclerosis (MS) in a high-risk Finnish population by studying the single nucleotide polymorphisms (SNPs) in the genes coding for critical enzymes and receptors involved in the melatonin pathway. A total of 590 subjects (193 MS patients and 397 healthy controls) were genotyped for seven SNPs in four genes including tryptophan hydroxylases (TPH)1 and 2, arylalkylamine N-acetyltransferase (AANAT) and melatonin receptor 1B (MTNR1B). An overrepresentation of T allele carriers of a functional polymorphism (G-703T, rs4570625) in the promoter region of TPH2 gene was observed in the progressive MS subtypes. The haplotype rs4570625-rs10506645TT of TPH2 gene was associated with the risk of severe disability in primary progressive MS (PPMS), while haplotype rs4570625-rs10506645TC appeared to be protective against disability in secondary progressive MS (SPMS). In the MTNR1B gene, the haplotype rs10830963-rs4753426GC was associated with the risk of SPMS, whereas another haplotype rs10830963-rs4753426GT showed an association with the risk of PPMS. These data showing the association of polymorphisms in the TPH2 and MTNR1B genes with the progressive subtypes of MS and disability suggest dysregulation in melatonin pathway. Melatonin pathway seems to be involved in disease progression, and therefore its potential effects in overcoming MS-related neurodegeneration may be worth evaluating in future clinical trials.
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