LecturePatient will present as → a 2-month-old infant with blond hair, blue eyes, and fair skin. He has microcephaly and a progressive impairment of cerebral function. On physical examination you notice an eczematous rash and the patient is vomiting. In addition he has a musty, mousy odor.
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Phenylketonuria (PKU) is an autosomal recessive disorder and inborn error of metabolism involving absent or virtually absent phenylalanine hydroxylase (PAH) enzyme activity.
- Phenylalanine and its metabolites accumulate in the central nervous system, causing mental retardation and movement disorders.
- Infants are normal at birth - after a few months, mental retardation is evident.
- Presents as blond, blue-eyed, with fair skin, mental retardation, eczema, and a musty, mousy body odor of phenylacetic acid.
- Neonates are screened for PKU 24 to 48 h after birth.
Routine neonatal screening
- In the US and many developed countries, all neonates are screened for PKU 24 to 48 h after birth with one of several blood tests; abnormal results are confirmed by directly measuring phenylalanine levels.
- Phenylketonuria is said to be present when plasma phenylalanine levels exceed 20 mg/dl.
Treatment is lifelong dietary phenylalanine restriction.
- All natural protein contains about 4% phenylalanine. Therefore dietary staples include low-protein natural foods (eg, fruits, vegetables, certain cereals).
- The sweetener aspartame can act as poisons for people with phenylketonuria.
Question 1 |
Which of the following is not true regarding phenylketonuria?
It is an autosomal dominant disorder | |
It is almost always associated with intellectual disability Hint: See A for explantion | |
Incidence in the US is 350 cases per 1 million live births Hint: See A for explantion | |
It is due to deficiency of the enzyme phenylalanine hydroxylase Hint: See A for explantion |
Question 1 Explanation:
Phenylketonuria is an autosomal recessive disorder. All other statements are correct.
Question 2 |
The skin findings of a patient with phenylketonuria include all of the following except
Fair skin and hair Hint: See C for explanation | |
Atopic dermatitis | |
Psoriasis | |
Scleroderma like plaques |
Question 2 Explanation:
Psoriasis is not a skin manifestation of phenylketonuria.
Children with PKU tend to have a lighter skin, hair, and eye color than unaffected family members, and some may develop a rash similar to infantile eczema.
Question 3 |
Classic phenylketonuria is said to be present when plasma phenylalanine levels exceed
5 mg/dl Hint: See D for explanation | |
10 mg/dl Hint: See D for explanation | |
15 mg/dl Hint: See D for explanation | |
20 mg/dl |
Question 3 Explanation:
Classic phenylketonuria is said to be present when plasma phenylalanine levels exceed 20 mg/dl.
Question 4 |
When is PKU testing performed
24 weeks gestation | |
24 to 48 h after birth | |
48 to 72 h after birth | |
at the first well child visit |
Question 4 Explanation:
In the US and many developed countries, all neonates are screened for PKU 24 to 48 h after birth. Tandem mass spectrometry is the method of choice. It has a low false-positive rate, and excellent accuracy and precision.
Question 5 |
How often should the phenylalanine levels of infants undergoing treatment for phenylketonuria be monitored?
Weekly | |
Twice a week Hint: for neonates | |
Monthly Hint: for children older than age 2 up till adulthood. | |
Biweekly Hint: for toddlers |
There are 5 questions to complete.
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