PAH and Hyperphenylalaninemia: Hyperphenylalaninemia (HPA), a disorder resulting in levels of phenylalanine that are excessive, is caused by a deficiency of the hepatic phenylalanine-4-hydroxylase (PAH) or its cofactor tetrahydrobiopterin (BH4), and clinically presents with a number of neurological signs and symptoms, such as irritability, hyperkinesis, and severe cognitive deficiency, often associated with TBM (Blau et al., 2014).