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If a child is not diagnosed during the routine newborn screening test and a phenylalanine-restricted diet is not introduced, then phenylalanine levels in the blood will increase over time. Toxic levels of phenylalanine (and insufficient levels of tyrosine ) can interfere with infant development in ways that have permanent effects.
Fumarylacetoacetate hydrolase (FAH) is a protein homodimer which cleaves fumarylacetoacetate at its carbon-carbon bond during a hydrolysis reaction. [8] As a critical enzyme in phenylalanine and tyrosine metabolism, 4-Fumarylacetoacetate hydrolase catalyzes the final step in the catabolism of 4-fumarylacetoacetate and water into acetoacetate, fumarate, and H + respectively. [9]
Phenylalanine is a precursor for tyrosine, the monoamine neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), and the biological pigment melanin. It is encoded by the messenger RNA codons UUU and UUC. Phenylalanine is found naturally in the milk of mammals.
Tetrahydrobiopterin deficiency (THBD, BH 4 D) is a rare metabolic disorder that increases the blood levels of phenylalanine.Phenylalanine is an amino acid obtained normally through the diet, but can be harmful if excess levels build up, causing intellectual disability and other serious health problems.
Phenylalanine concentrations are routinely screened in newborns by the neonatal heel prick (Guthrie test), which takes a few drops of blood from the heel of the infant. Standard phenylalanine concentrations in unaffected persons are about 2-6mg/dl (120–360 μmol/L) phenylalanine concentrations in those with untreated hyperphenylalaninemia can ...
Tyrosine is semi-essential; therefore, it can be synthesized by the animal, but only from phenylalanine. Phenylketonuria, a genetic disorder that occurs as a result of the inability to breakdown phenylalanine, is due to a lack of the enzyme phenylalanine hydroxylase. A dietary lack of tryptophan can cause stunted skeletal development. [9]
4-Hydroxyphenylpyruvic acid (4-HPPA) is an intermediate in the metabolism of the amino acid phenylalanine. The aromatic side chain of phenylalanine is hydroxylated by the enzyme phenylalanine hydroxylase to form tyrosine. The conversion from tyrosine to 4-HPPA is in turn catalyzed by tyrosine aminotransferase. [2]
Patients received amino acid supplements lacking tyrosine and phenylalanine, most often by drinking a specially engineered formula, in order to acquire sufficient protein. It is recommended that tyrosine levels remain below 500 μmol/L. [5] Phenylalnine is the precursor to tyrosine. The ideology behind maintaining low tyrosine levels is two-fold.