Examples include aromatic L-amino acid decarboxylase (AADC) deficiency, lysosomal storage disorders such as Tay-Sachs Disease (TSD), neuronal ceroid lipofuscinoses (Batten Disease), mucopolysaccharidoses, and leukodystrophies (Canavan Disease), Huntington’s disease and neuromuscular disorders such as spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD). Here, DDC is linked to Tay-Sachs disease.