Test reveals infant's rare disorder
The baby's birth brought a lot of excitement and joy to his parents and immediate family, but his arrival was smooth and blissfully uneventful for the delivering obstetrician and the hospital's neonatology team. During the first week of life, the newborn continued to behave himself, breast feeding and sleeping and filling his diapers like a champ.
It wasn't until day seven that the fateful call came through to the pediatrician's office. The department of public health phoned the physician to report an abnormality in the state-required newborn screen, which, per hospital routine, had been performed after the baby reached 24 hours of age. The screening test - a simple heel stick blood test collected on filter paper and sent off to the state laboratory - revealed the little boy suffered from a rare congenital metabolic condition known by the shorthand PKU.
The appropriately concerned parents made an appointment with a well-known metabolic expert at the genetics department of the city's pediatric hospital. The boy was just beginning what was to be a lifetime of careful laboratory monitoring and frequent visits to the downtown specialist. His mom and dad were also initiated as PKU parents, getting a quick but thorough education on the modified diet their child would need to prevent the development of subsequent mental retardation.
PKU, or phenylketonuria, is inherited as an autosomally recessive condition, so both parents must carry the abnormal gene in order for the child to be affected. Johns Hopkins University geneticists report that this condition occurs in approximately one in 10,000 births, and is caused by a deficiency of the liver enzyme phenylalanine hydroxylase. Because of this deficiency, children with PKU have a limited ability to convert the essential amino acid phenylalanine into tyrosine. Left untreated, PKU results in a buildup of phenylalanine and its breakdown products, which are neurotoxic at high levels and therefore negatively impact the child's developing brain.
Researchers at the National Institutes of Health explain that the mainstay of PKU treatment requires strict adherence to a low phenylalanine diet not only during childhood, but ideally as a "diet for life." Pregnant women with PKU must be especially careful to follow the recommended diet both before conception and during pregnancy so that high levels of phenylalanine and its metabolites will not build up and harm the developing fetus.
The PKU diet involves limiting but not entirely eliminating phenylalanine, since a certain amount of this essential amino acid is needed for normal growth and development. Several specialized formulas have been developed to provide low-phenylalanine protein sources during infancy, as well as to serve as protein supplements during later childhood, adolescence and adulthood.
Academic pediatricians from the University of Texas at Galveston list sugar, oil, pure starch, and water as the only recognized phenylalanine-free foods. Foods high in protein, including meat, fish, eggs, dairy products, nuts, dried beans and dried peas, are naturally high in phenylalanine. Low-protein foods such as fruits, vegetables and cereals can function as controlled sources of phenylalanine.
The Texas group cautions that the artificial sweetener Aspartame is 56 percent phenylalanine and should always be avoided by individuals with PKU. Aspartame is used in many low-calorie foods and drinks and is also found as an ingredient in several over-the-counter vitamins and in certain prescription medications.
• Dr. Helen Minciotti is a mother of five and a pediatrician with a practice in Schaumburg. She formerly chaired the Department of Pediatrics at Northwest Community Hospital in Arlington Heights.