A number of conditions may be associated with an increased plasma phenylalanine.
DIfferential diagnosis of hyperphenylalaninemia:
(1) decreased activity of phenylalanine hydroxylase (PAH)
(1a) classic phenylketonuria with no PAH activity
(1b) partial PAH activity
(2) disorder of BH4 metabolism
(2a) guanosine triphosphate cyclohydrolase (GTPCH) deficiency
(2b) 6-pyruvoyl tetrahydropterin synthase (PTPS) deficiency
(2c) pterin-4 acarbinolamine dehydratase (PCBD) deficiency
(2d) dihydropteridine reductase (DHPR) deficiency
(3) transient elevation of plasma phenylalanine
(3a) liver disease
(3b) prematurity
(3c) sepsis
(3d) severe burns
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Specialty: Endocrinology, Clinical Laboratory, Genetics
