DDC and schizophrenia: Polymorphisms in DDC, the gene the encoding dopa decarboxylase which converts L-DOPA into dopamine, have been associated with the age of onset of schizophrenia in male patients (Borglum et al., 2001), although other studies found no association in paranoid schizophrenia (Hoogendoorn et al., 2005; Talkowski et al., 2008).