As an example, multiple sclerosis (MS) has a small but significant shift for the codon employment in the AU3 codon direction (inset in Fig. 8b), while Parkinson’s disease and amyotrophic lateral sclerosis (ALS) in the gray matter correlate to a codon employment shift towards the GC3 codon direction, probably in the effort of promoting GP2 genes, and thereby inducing the differentiation of neuronal precursors (for a more detailed discussion about the codon employment shift in different diseases see Additional files 8, 9, 10, 11, 12, 13, 14, 15, 16 and 17). The gene discussed is GP2; the disease is Parkinson disease.