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Clinical Case Presentation # 5. Building Blocks of Life Phenylketonuria . There will be a test at the end of this presentation!. 24 year old female Weighs 55 kg. Chief Complaint (CC) Here for a check-up. Has some cold sensitivity on lower left molar History of Chief Complaint (HCC)

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Clinical Case Presentation # 5

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clinical case presentation 5

Clinical Case Presentation# 5

Building Blocks of Life Phenylketonuria

24 year old female weighs 55 kg
24 year old femaleWeighs 55 kg
  • Chief Complaint (CC)
    • Here for a check-up. Has some cold sensitivity on lower left molar
  • History of Chief Complaint (HCC)
    • Noticed cold sensitivity over past couple of months
  • Social History (SH)
    • No history of smoking/illicit drug use.

Drinks vodka and grapefruit juice 5 x/wk


Nutritional History (NH)

    • Eats a very strict diet which is low in protein and high in carbohydrates. She eats/drinks frequently (approx 6 times/day), and takes phenylalanine free amino acid supplement drinks 4 times a day (directly from the bottle).
  • Family History (FH)
    • Mother is homozygous for PKU gene
    • mutation
Dental History (DH)
    • Last check-up 5 years ago. Had a number of amalgam fillings 7 years ago. Brushes twice a day, doesn’t floss.
  • Medical History (MH)
    • Phenylketonuria. Monthly blood testing (Guthrie test) reveals phenylalanine levels within normal limits over last 5 years.
  • Medications
    • None
  • Review of Systems (RS)
    • Fair skin, blonde hair, dry skin, eczema, below average IQ.
examination findings
Examination Findings
  • Extra-oral exam WNL
  • Generalized enamel erosion of all tooth surfaces.
  • Lower left first molar sensitive to ice applied to the occlusal aspect.
  • Low plaque index
Diagnosis and Risk AssessmentAre any of the conditions in the history connected to the enamel erosion ?
  • Phenylketonuria ?
  • Vodka and grapefruit juice?
  • Low protein diet ?
  • High carbohydrate diet ?
  • Frequent eating/drinking ?
  • Long-time between dental check-ups ?
  • Doesn’t floss ?
  • Below average IQ ?
differential diagnosis
Differential Diagnosis
  • Bulemia nervosa: gastric acid regurgitation
  • Erosion due to chronic consumption of low pH drinks
  • Saliva with poor buffering capacity
  • Poor oral hygiene
  • Salivary pH at rest is 6.5, stimulated is 7.0
  • Patient drinks daily: 4 servings of lemonade (pH3.1), and 4 servings of supplement drink (pH 4.1). She never uses a straw.
  • No history of vomiting or gastric reflux.
phenylketonuria pku
Phenylketonuria (PKU)
  • PKU is an inborn error of metabolism from deficiency of the enzyme, phenylalanine hydroxylase (found in the liver), or more rarely, of its tetrahydrobiopterin cofactor .
  • The incidence of PKU is approximately 1 in 14,000 in only the white population of the United States (Celtic origin).
  • The hydroxylation of PHE is a required step in both the normal degradation of the carbon skeleton of this amino acid and the synthesis of tyrosine.
  • The normal blood level of PHE is 30-120 μM (0.5 to 2.0 mg/dL), but it is >1200 μM (20 mg/dL) in phenylketonurics.
  • Leads to excessive urinary excretion of phenylpyruvate and phenyllactate, and, if untreated leads to severe mental retardation.
  • Newborn screening for PKU is mandatory in the United States. Prenatal diagnosis is now possible using DNA probes
clinical manifestations
Clinical manifestations
  • Decreased pigmentation: PHE is a competitive inhibitor of tyrosinase in melanocytes.
  • Neurological defects: attributed to toxic effects of phenylalanine, possibly because of reduced transport and metabolism of other aromatic amino acids in the brain due to competition from the high phenylalanine concentration. Patients may have low IQ, spasticity and a history of seizures.

PKU can be caused by an intron mutation that leads to aberrant splicing. (A) Normal primary transcript and mRNA. (B) Mutation of G to A in intron 12 results in the skipping of exon 12. Most mutations causing PKU occur in coding regions.


Treatment & Prognosis

  • Phenylketonuria is treatable by a low phenylalanine diet continued indefinitely. Patients with PKU should avoid artificial sweeteners (Aspartame). If the Phe levels are kept normal, prognosis is excellent.
  • Gene therapy is in development.
  • The plant enzyme phenylalanine ammonia lyase (PAL) will survive in the gut long enough to deplete the phenylalanine derived from food protein and so reduce the rise in blood phenylalanine that otherwise occurs after a protein meal. Studies are in progress.
answer the following
Answer the following
  • What are this patient’s risk factors for enamel erosion ?
  • What is the pathogenesis of PKU ?
  • As a dentist, what recommendations would you make to patients &/or parents of patients with PKU ?