DDC and aromatic L-amino acid decarboxylase deficiency: Key markers of AADC deficiency in CSF analysis include: (1) low levels of 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), (2) high levels of 3-ortho-methyldopa (3-OMD), L-dopa and 5-OH tryptophan due to metabolic block with reduced/absent AADC activity, (3) normal pterins, including neopterin and biopterin.