Amino Acid Disorders

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Disease Name Phenylketonuria
Alternate name(s) Hyperphenylalaninemia, Phenylalanine hydroxylase deficiency, Følling disease
Acronym PKU
Disease Classification Amino Acid Disorder
Variants Yes
Variant name

Benign phenylketonuria, Mild phenylketonuria, Variant phenylketonuria, Biopterin-responsive phenylketonuria

Tetrahydrobiopterin deficiencies:
GTP cyclohydrolase I deficiency, 6-Pyruvoyl-tetrahydropterin synthase deficiency, Dihydropteridine reductase deficiency, Pterin-4_-carbinolamine dehydratase deficiency

Symptom onset Infancy
Symptoms Mental retardation, decreased pigmentation relative to family members, eczematous rash, seizures, abnormal gait, and unusual “mousy” odor to urine.
Natural history without treatment Mental retardation in the moderate to severe range, hyperactivity, eczema, mild neurologic manifestations, possible abnormal gait microcephaly.
Natural history with treatment If diet instituted early, normal IQ and development can be expected.
Treatment Dietary restriction of phenylalanine with supplementary formula for tyrosine and essential amino acids.
Other “Mousy” or “musky” smelling urine. Females with PKU are at-risk to have children affected by maternal PKU (increased levels of phenylalanine are teratogenic).
Physical phenotype No abnormalities present at birth. May develop widely-spaced incisors, pes planus, epicanthus and microcephaly.
Inheritance Autosomal recessive
General population incidence 1:10,000
Ethnic differences Yes
Population Turks, Irish
Ethnic incidence Turks (1:2600), Irish (1:4500)
Enzyme location Liver
Enzyme Function Converts phenylalanine to tyrosine
Missing Enzyme Phenylalanine hydroxylase
Metabolite changes Increased plasma phenylalanine, increased phenylpyruvic acid in urine, decreased plasma tyrosine.
Gene PAH (E.C
Gene location 12q24.1
DNA testing available Yes
DNA testing detail Direct and linkage testing available. Over 380 mutations have been identified in PAH gene and direct DNA testing is available on limited clinical basis.
Prenatal testing DNA testing is possible if mutations known. RFLP analysis is successful in 75% of families.
MS/MS Profile N/A
Genetests Link
Support Group

National Urea Cycle Disorders Foundation

National Coalition for PKU and Allied Disorders

Children Living with Inherited Metabolic Diseases

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