TH and Alzheimer disease: These conditions include disorders of biogenic amine synthesis, such as tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC) defects, and disorders of tetrahydrobiopterin cofactor metabolism, comprising autosomal-dominant (AD) GTPCH deficiency and 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency (Morales-Briceño et al. 2020; Leuzzi et al. 2021).