Phenylketonuria (NORD)
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Phenylketonuria (NORD)
Genetics
Genetic disorders
Achondroplasia
Alagille syndrome (NORD)
Familial adenomatous polyposis
Familial hypercholesterolemia
Hereditary spherocytosis
Huntington disease
Li-Fraumeni syndrome
Marfan syndrome
Multiple endocrine neoplasia
Myotonic dystrophy
Neurofibromatosis
Polycystic kidney disease
Treacher Collins syndrome
Tuberous sclerosis
von Hippel-Lindau disease
Albinism
Alpha-thalassemia
Beta-thalassemia
Cystic fibrosis
Friedreich ataxia
Gaucher disease (NORD)
Glycogen storage disease type I
Glycogen storage disease type II (NORD)
Glycogen storage disease type III
Glycogen storage disease type IV
Glycogen storage disease type V
Hemochromatosis
Krabbe disease
Leukodystrophy
Mucopolysaccharide storage disease type 1 (Hurler syndrome) (NORD)
Niemann-Pick disease type C
Niemann-Pick disease types A and B (NORD)
Phenylketonuria (NORD)
Polycystic kidney disease
Primary ciliary dyskinesia
Sickle cell disease (NORD)
Tay-Sachs disease (NORD)
Wilson disease
Cri du chat syndrome
Williams syndrome
Angelman syndrome
Prader-Willi syndrome
Beckwith-Wiedemann syndrome
Mitochondrial myopathy
Klinefelter syndrome
Turner syndrome
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Friedreich ataxia
Huntington disease
Myotonic dystrophy
Down syndrome (Trisomy 21)
Edwards syndrome (Trisomy 18)
Patau syndrome (Trisomy 13)
Alport syndrome
Fragile X syndrome
Fabry disease (NORD)
Glucose-6-phosphate dehydrogenase (G6PD) deficiency
Hemophilia
Lesch-Nyhan syndrome
Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)
Muscular dystrophy
Ornithine transcarbamylase deficiency
Wiskott-Aldrich syndrome
X-linked agammaglobulinemia
Autosomal trisomies: Pathology review
Miscellaneous genetic disorders: Pathology review
Muscular dystrophies and mitochondrial myopathies: Pathology review
Assessments
Phenylketonuria (NORD)
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External References
First Aid
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2016
Cofactors
phenylketonuria p. 81
Congenital heart disease p. 304-306
maternal phenylketonuria p. 82
Eczema
phenylketonuria p. 82
Microcephaly
maternal phenylketonuria p. 82
Phenylketonuria p. 82, 82
Pregnancy p. 657
maternal phenylketonuria p. 81
Seizures p. 535
phenylketonuria p. 82
Transcript
Content Reviewers
Phenylketonuria or PKU is a rare metabolic disease that can lead to severe brain disorders caused by the accumulation of the amino acid phenylalanine to toxic levels in the blood and brain.
Amino acids are the basic building blocks that make up proteins. Phenylalanine, or Phe, is one of the essential amino acids. It is necessary for life, but our bodies can't make it; therefore, Phe must be acquired through foods that contain protein. Normally, once Phe enters the body, most of it is converted to tyrosine by the enzyme phenylalanine hydroxylase. Tyrosine is then turned into neurotransmitters important for normal brain development and function.
PKU is an autosomal recessive genetic disorder that affects function of the phenylalanine hydroxylase enzyme. The phenylalanine hydroxylase gene is located on chromosome 12 and over 600 mutations have been described. The degree of enzyme function can vary. When untreated, people with PKU develop symptoms such as severe intellectual disability, psychiatric disorders, and seizures. A pregnant woman with PKU must pay special attention to her Phe levels to reduce the risk of Maternal PKU Syndrome that can result in heart defects, microcephaly, and developmental disability in her baby.
In PKU, elevated Phe levels and reduced tyrosine levels can change the way the brain functions. This is because Phe uses the same transporters to get across the blood-brain barrier as other amino acids including- tyrosine and tryptophan. Tyrosine is needed to synthesize dopamine and norepinephrine, and tryptophan is needed to synthesize the neurotransmitter serotonin. As Phe levels rise, it occupies all the transporters, making it hard for tyrosine and tryptophan to get across the blood-brain barrier. As a result, dopamine, norepinephrine, and serotonin levels in the brain begin to fall, leading to abnormal brain development and intellectual disability.
Summary
Phenylketonuria (PKU) is an autosomal recessive amino acid metabolism disorder involving impaired metabolism of the amino acid phenylalanine, caused by the absence or reduced activity of phenylalanine hydroxylase. In PKU toxic levels of phenylalanine and phenylketone build up in the body and tyrosine levels drop.
Symptoms include a musty odor of sweat and urine, intellectual disability, seizures, behavioral problems, and other neurological symptoms. In pregnant females, PKU can affect the fetus - causing heart disease, growth problems, intellectual disability, and microcephaly. Treatment is based on a diet with low levels of phenylalanine and supplementing with tyrosine and tetrahydrobiopterin.
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