• although newborn screening for PKU has been routine throughout North America since the 1960's, it is not routine in undeveloped countries (beware immigrants, foreign visitors)
• PKU is caused by phenylalanine hydroxylase (PAH) deficiency which catalyzes the conversion of phenylalanine to tyrosine
• neonates with PKU typically show no physical signs of hyperphenylalaninemia
• children with untreated PKU have impaired brain development with poor brain growth, seizures, behavior problems, and severe mental retardation
• affected individuals exude a pungent, musty odor due to elevated phenylalanine levels which also causes skin conditions such as eczema
• because there is absent tyrosine production with reduced tyrosinase, the hair and skin are very lightly pigmented
• early diagnosis and management with a low-phenylalanine diet eliminates these complications; and once treated, affected children are healthy and do not require hosopitalizations

References

Rimoin DL, Connor JM, Pyeritz RE, eds. Emergy adn Rimoin's Principles and Practice of Medical Genetics. 4th ed. New York, NY: Churchill Livingstone; 2002

Ryan S, Scriver CR. Phenylalanine hydroxylase deficiency. GeneReviews. Seattle, Wash: Children's Health System and University of Washington; 2003.