Noticeably, western blot showed that TH levels were reduced in the midbrain of 15-month-old mice compared to that in 2-month-old mice; however, such age-associated changes were not evident in the KO mice (Fig. 7F, G), suggesting that aging is the most prominent risk factor for PD and that Maged1 knockout could block age-related DA degeneration. The gene discussed is TH; the disease is Parkinson disease.