The Work of Managing Phenylketonuria and Breastfeeding

Research Article

Ann Nurs Res Pract. 2016; 1(2): 1006.

The Work of Managing Phenylketonuria and Breastfeeding

Banta-Wright SA1,2*, Houck GM³, Kodadek SM4, Steiner RD5,6 and Knaf¹ KA7

1School of Nursing, George Fox University, USA

2Department of Pediatric Medicine, Randall Children’s Hospital, USA

3School of Nursing, University of Washington, USA

4School of Nursing, Oregon Health & Science University, USA

5School of Medicine, Oregon Health & Science University, USA

6School of Medicine and Public Health, University of Wisconsin, USA

7School of Nursing, University of North Carolina, USA

*Corresponding author: Sandra Banta-Wright, School of Nursing, George Fox University, 414 North Meridian Street, Newberg, Oregon 97132, USA

Received: July 07, 2016; Accepted: August 02, 2016; Published: August 04, 2016


Purpose: To describe the demands of breastfeeding in the context of Phenylketonuria (PKU) and mothers’ efforts to manage the complicated feeding regimen.

Design and Methods: A qualitative design and methods were used to interview mothers (n=10) who had previously completed an online international survey about their feeding experiences with their infants with PKU. Mothers were recruited to participate in in-depth telephone interviews to further explore their breastfeeding experiences of their infants with PKU. Mothers were eligible for participating in the study if they were 21 years of age or older, had initiated breastfeeding an infant with PKU, and the infant was less than three years of age. There were no restrictions on the length of time mothers’ breastfed.

Results: The work of adapting breastfeeding to maintain phenylalanine levels was the central theme of the breastfeeding experience. Mothers described two major components of the work and effort needed to breastfeed infants with PKU: maintaining phenylalanine levels and adapting breastfeeding.

Practice Implications: Mothers used various strategies to sustain breastfeeding while adhering to the PKU management plan in order to successfully manage their infants’ PKU and breastfeeding.

Keywords: Breastfeeding; Inborn error of metabolism; Infant-newborn; Lactation; Phenylalanine; Phenylketonuria


IRB: Institutional Review Board; kg: Kilogram; PAH: Phenylalanine Hydroxylase; Phe: Phenylalanine; PKU: Phenylketonuria; μmol/L: Micromole per Liter


Phenylketonuria (PKU) is the most common inborn error in amino acid metabolism [1]. Although the occurrence of PKU varies across groups, it is present in every ethnic and racial group. Normally, the enzyme Phenylalanine Hydroxylase (PAH) metabolizes Phenylalanine (Phe) into tyrosine in the liver. In PKU, PAH is defective and results

in excessive concentrations of Phe in the blood and eventually toxic concentrations in the brain. The different mutations in the gene-coding PAH enzyme determines the clinical presentation and severity of the disorder. The combinations of the different mutations result in varying degrees of residual PAH activity [2]. The residual PAH enzyme reflects Phe tolerance.

Untreated PKU results in the slow insidious loss of neurocognitive skills resulting in permanent cognitive impairment as the child grows. Classical signs include eczema like skin rash, excessive restlessness, and a “musty” or “mousy” odor of the body, urine and perspiration due to phenylacetate accumulation. In addition, individuals affected with PKU have a lighter coloration of skin, hair, and eyes. Developmental problems, irritable behavior, gait disturbances, psychiatric symptoms, and impaired cognition become clinically present with increasing toxic accumulation within the body and brain.

Newborns with PKU appear normal at birth. In the past as they grew, these children were identified after the insidious insult had occurred and they had suffered permanent neurocognitive sequela [3]. Robert Guthrie’s introduction of a simple diagnostic screening test for PKU allowed for mass screening and identification of PKU before the presence of clinical signs became detectable [4]. Early identification and prompt dietary intervention with a Phe-restricted diet means children with PKU can avoid the neurocognitive insult. The Phe-restricted diet limits daily dietary Phe intake and requires a supplementation of synthetic amino acid fortified medical foods and beverages to ensure low-Phe to Phe- free protein sources with adequate nutritional value for normal growth and development.

During the early years of PKU management, infants diagnosed with PKU were immediately weaned from breastfeeding. The dietary treatment consisted of a low-Phe medical formula in conjunction with standard commercial infant formula. This combination was believed to be the only effective way to manage the infant’s Phe intake and allow for precise titration and measurement of Phe based on serial infant heel sticks [5]. This management strategy thus precluded breastfeeding infants with PKU [6-9].

However, breast milk has many advantages when offered as a primary source of nutrition for infants with PKU. These include the normal benefits of breastfeeding and breast milk for any infant [10,11]. In addition, Phe concentration is lower in mature breast milk (2,482 μmol/L) [12,13] than standard commercial infant formula, such as Mead Johnson Enfamil® (4,419 μmol/L) [8] making it possible to utilize a higher proportion of natural protein. For infants with PKU, Phe restriction means breast milk must be limited and adjusted based upon weekly blood Phe levels. Breast milk intake, whether from breastfeeding or breast milk feedings, must be adapted to maintain desired Phe levels (120-360 μmol/L) [14,15] that are dependent upon the infant’s residual PAH activity. Therefore, the addition of Phe-free medical formula is essential in order to provide adequate caloric and protein intake while maintaining Phe restriction for normal cognitive and behavioral development.

Results from numerous studies [8, 9,16-20] consistently reported breast milk supplemented with Phe-free medical formula was an acceptable dietary treatment for infants with PKU because Phe levels could be maintained within the desired range despite the challenge that Phe intake was difficult to determine precisely in the context of breastfeeding. Yet, there are no universal approach to breastfeeding infants with PKU and supplementing with Phe-free medical formula. Consequently, mothers typically offer breast milk by one of three options based upon recommendations from their metabolic health care providers, usually a dietitian. Mothers provided 1) a fixed volume of Phe-free medical beverage followed by breastfeeding until satiety [9,21]; 2) a fixed volume of expressed breast milk or a fixed time limitation of breastfeeding followed by Phe-free medical beverage until satiety [22]; and 3) alternating feedings between breastfeeding and Phe-free medical beverage [19].

Studies reveal few mothers of infants with PKU persist in breastfeeding after diagnosis [7,9,16,18,19,23-27]. Overall, the incidence, prevalence, and duration of breastfeeding when infants have PKU are lower when compared to other full-term infants who do not have PKU. For example, in an Israeli study, breastfeeding rates were significantly lower in infants with PKU than in the general Israeli population [26]. In a more recent study involving mothers from the United States and Canada, the prevalence of breastfeeding infants with PKU before and after diagnosis revealed significantly fewer mothers were breastfeeding after diagnosis [25]. However, there are no published reports describing mothers’ experiences breastfeeding infants with PKU to help understand how women sustain breastfeeding within this unique population. Therefore, the purpose of this study was to examine the demands of breastfeeding in the context of PKU and mothers’ efforts to manage the complex feeding regimen.



This study utilized a two-phase mixed methodology. Phase one was the quantitative phase with an Internet survey completed by mothers residing in the United States and Canada about their experiences feeding infants with PKU. Mothers were recruited from a variety of social media options including the PKU listserv, Facebook, Twitter, and national/regional PKU associations. The goal of the quantitative phase was to explore the rate of breastfeeding before and after diagnosis of PKU in the sample. In the phase one sample, 103 mothers had one child with PKU while 16 mothers had two or more children with PKU. Overall, mothers with one child with PKU were in their thirties (n=64, mode=34) but ranged from age 21 to 63 years, were married/partnered, and well-educated as all mothers were high school graduates and more than two-thirds (n=72) were college graduates. Initially 89 mothers with one child breastfed, but after the PKU diagnosis, only 72 mothers continued to breastfeed. This decrease in breastfeeding was significant (McNemar’s χ2 = 30.333, p < .001; n = 72 versus n = 89) [25].

Phase two of the study was qualitative telephone interviews with a subset of mothers from phase one to provide a more detailed understanding of the maternal experience of breastfeeding infants with PKU and the meaning that the mothers attributed to their experiences. The study was approved by the institutional review board (IRB) of Oregon Health & Sciences University.

Sample and setting

Mothers were eligible for participating in the qualitative phase two if they were 21 years of age or older and had initiated breastfeeding an infant with PKU. There were no restrictions on the length of time mothers’ breastfed. In addition, the breastfed infant with PKU needed to be less than 36 months old at the time of the telephone interview. Of the 103 mothers who participated in the Internet survey and expressed a willingness to be interviewed, 23 mothers met the sample criteria for phase two of the study. This subset of mothers was predominantly Caucasian, well-educated, in their 30’s, and had breastfed for at least four months. Ten mothers were purposely recruited to participate in the telephone interviews to reflect a broad range of demographic variables: 1) urban versus rural residence, 2) ethnicity, 3) gravida status, 4) education, 5) marital status, 6) employment, and 7) household income. Demographic characteristics of the mothers and infants are presented in the Table 1.