Phenylketonuria Clinical Presentation
- Author: Georgianne L Arnold, MD; Chief Editor: Luis O Rohena, MD more...
Most individuals with phenylketonuria (PKU) appear normal at birth. If newborn screening fails, progressive developmental delay is the most common presentation. Other findings in untreated children in later infancy and childhood may include vomiting, mousy odor, eczema, seizures, self-mutilation, and severe behavioral disorders.
Older individuals who cease dietary treatment in childhood may have evidence of demyelination on MRI. Occasionally, deterioration of cognitive performance or motor skills also may be present. Intelligence quotients (IQs) may drop by 10 points or more if the diet is stopped in midchildhood.
The clinical manifestations of PKU are largely of historical interest, because the damaging features of the disease are virtually always prevented through early diagnosis and treatment. Skin findings are as follows:
- Fair skin and hair – This is the most characteristic skin manifestation, resulting from impairment of melanin synthesis (see the image below); it can be striking in black and Japanese patients, although not all untreated patients are fair, and treated patients often have typical pigmentation
- Eczema (including atopic dermatitis)
- Light sensitivity
- Increased incidence of pyogenic infections
- Increased incidence of keratosis pilaris
- Decreased number of pigmented nevi
- Sclerodermalike plaques
- Hair loss
Other manifestations of untreated PKU are as follows:
- Intellectual disability (the most common finding overall)
- Musty or mousy odor
- Epilepsy (50%)
- Extrapyramidal manifestations (eg, parkinsonism)
- Eye abnormalities (eg, hypopigmentation)
Subtle attention and performance deficits in organization and planning persist in treated patients. These deficits are in some cases related to phenylalanine levels and may interfere with academic achievement.
A few patients experience psychological problems, including poor self-esteem. Agoraphobia and more severe problems have been described, especially in women who have discontinued the treatment. Because phenylalanine competes with tryptophan (the precursor of serotonin) for entry into the brain, psychological symptoms may have a biological basis and improved dietary control is recommended.
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