Levodopa (L-dopa), the dopamine precursor and the gold standard for the treatment of PD (Salat and Tolosa, 2013) is usually taken in combination with a dopa decarboxylase inhibitor, such as carbidopa to prevent early conversion into dopamine prior to reaching the brain (van Kessel et al., 2019). The gene discussed is DDC; the disease is Parkinson disease.