Summary

INTRODUCTION

Phenylketonuria (PKU) is an autosomal recessive genetic disorder where phenylalanine is not converted to tyrosine in the liver as phenylalanine hydroxylase is absent. Excess phenylalanine accumulates in the body and forms phenyl pyruvic acid, which damages central nervous system (CNS) cells. Normal treatment for PKU involves limiting intake of Phenylalanine. Before, PKU babies were immediately weaned from breastfeeding and fed with phenylalanine-free formula and standard formula but after researchers discovered that breast milk had lower levels of phenylalanine than standard formula, PKU babies could alternatively be fed with breast milk and phenylalanine-free formula.

 However, fewer PKU babies were breastfed than normal babies and PKU babies were weaned earlier than normal babies.

As there are no studies about breastfeeding incidence and period of PKU babies in America, thus the aim of this experiment is to find out if breastfeeding is applicable for American PKU babies by comparing average phenylalanine levels in breastfed and formula-fed PKU babies.

Methods:

This study was done in 2 hospitals with a total of 560 patient beds. One of the hospital is a children’s hospital and is only pediatric metabolic clinic program in the state. Hence, all infants diagnosed with PKU are referred to. The retrospective chart review took place from 2006 to 2008. Serial information on the Phe levels, infants’ medical, dietary and clinical records that provided assessments of the infant from both dietitian and medical perspectives provided the data. Using a medical record abstraction tool, data were collected. The frequency of measuring phenylalanine levels is based on the infant’s age and phenylalanine tolerance. This is done by using Guthrie cards (specific filter paper onto which blood from a heel-prick is saturated). Generally, phenylalanine levels will be assessed from every other day to twice a week depending on phenylalanine level in blood. From 2002 till now, tandem mass spectrometry is used to determine phenylalanine levels. Before that, phenylalanine levels have been measured using an amino acid analyser. Being more sensitive and specific, tandem mass spectrometry has improved the detection of inborn errors of metabolism such as PKU.

RESULTS

5 levels of Phe levels were taken from each infant (inclusive of the two newborn-screen results and confirmatory test, which were elevated, thus skewing the data and hence were taken out of consideration) to measure mean Phe levels for breastfed and formula- fed PKU infants. Results show that more breastfed PKU babies (80%) than formulae-fed PKU babies (72%) had a good mean Phe levels (120–360 μmol/L). This means that breastfed PKU babies had a better chance of having desirable Phe levels. Formula-fed babies had a higher chance of having too low mean Phe levels and the chances of having too high Phe levels were the same for both groups. Infants with PKU living in the central and coastal regions of Oregon have significantly higher mean Phe levels.

Discussion:

Despite it being breast-fed or bottle-fed, most infants have similar phenylalanine levels during the first year of life. Overall, more breast-fed infants with PKU had phenylalanine levels within the normal range (120–360 μmol/L). This supports previous research that breast-fed infants with PKU can have phenylalaninelevels within the desired therapeutic range. We can only hypothesize why infants with PKU living in the central and coastal regions of Oregon have significantly higher mean Phe levels. Some possible causes are no/little access to the tertiary clinic, lack of a professional support or parental understanding for managing phenylalanine levels and the need to ensure phenylalanine level remains normal. To clarify why infants diagnosed with PKU have higher phenylalanine levels in the regions mentioned above, more research have to be done.