In the patients affected by CEP and PCT the expression levels of DBP and NFIL3 were significantly higher with regard to the patients affected by AIP, while significantly lower expression levels of ARNTL, CLOCK, CRY1, CRY2, CSNK1E, DBP NFIL3, NR1D1, PER2, and SIRT1 were found in symptomatic patients when compared to asymptomatic patients. The gene discussed is PER2; the disease is porphyria cutanea tarda.