Abstract Long Evans cinnamon (LEC) rat is an animal model for human Wilson disease (WD) due to a deletion in Atp7b, the copper transporter defective in WD patients. Previously, we have demonstrated presence of an alternative product termed PIneal Night-specific ATPase (PINA) generated by an intronic promoter in Atp7b gene. Analysis of LEC rat in this study demonstrates that PINA is absent in the LEC pineal establishing its usefulness for investigating PINA function. Studies of the LEC pineal, however, revealed an additional defect in serotonin N-acetyltransferase (NAT), the key enzyme in melatonin production. Linkage studies confirm that the NAT phenotype is entirely independent of PINA mutation in the pineal gland of LEC rats, and sequence analysis demonstrates that NAT defect is due to a point mutation in NAT coding region. In addition, we demonstrate that the cinnamon coat color of the LEC rat is unlinked to PINA and NAT deficiencies in these animals. To facilitate further functional analysis of PINA in pineal physiology, we crossed LEC rats with PVG rats that are wildtype for PINA, NAT and coat color, and obtained rats that are defective only in PINA/Atp7b locus (termed LPP rats) and normal for NAT activity and coat color. Furthermore, we have identified the deletion breakpoint of Atp7b gene in LPP rats, which allows simplified genotyping of mutant animals. The separation of PINA mutation from both NAT and coat color mutations in the new LPP rats will permit better functional studies of PINA in pineal circadian physiology.