NPAS2 and bipolar disorder: After Bonferroni correction, the rs6738097 variant in NPAS2 gene remained significantly associated and an additive effect was shown by the epistasis analysis between the rs6738097 variant in the NPAS2 gene and the rs1554338 variant in the CRY2 gene, proposing genetic variations in the NPAS2 gene as a valuable biomarker for a seasonal pattern of occurrence in bipolar disorder [86].