Comparison of phenylalanine tolerance in singleton and twin pregnancies in patients with phenylketonuria

Objectives

Empirical determination of phenylalanine (Phe) tolerance in patients with phenylketonuria (PKU) relies on frequent assessment of blood Phe concentrations in relation to Phe intake from detailed meal records. This study aimed to determine Phe tolerance in twin pregnancies.

Methods

The reviewed cases included three women with PKU who each had a singleton and twin pregnancy (i.e., they were pregnant twice). All patients were under regular supervision to maintain Phe concentrations in a steady state and determine safe Phe intake. Restriction of Phe in the patient’s diet was determined depending on the amount of Phe intake, which allowed for stable blood Phe concentrations within the target range.

Results

In all three patients with PKU, the ratio of Phe tolerance during the course of the twin and singleton pregnancies was <1 for most of the pregnancy. The ratio of the increase in Phe tolerance between 29 and 34 weeks of gestation and that between 15 and 28 weeks of gestation was 0.66 and 1.17, 0.51 and 0.14, and 0.76 and 1.42 in the twin and singleton pairs of pregnancies, respectively.

Conclusions

Our study shows that Phe tolerance in a twin pregnancy is not greater than that in a singleton pregnancy.

Low increase in phenylalanine tolerance during pregnancies in PKU woman with high prepregnancy BMI and postconceptional initiation of diet: A case report

Background

Women with untreated phenylketonuria (PKU) are at an increased risk to have offspring with multiple abnormalities due to teratogenic effects of hyperphenylalaninaemia. Treatment goals include blood phenylalanine concentrations between 120 and 360 µmol/L, however, there are limited pieces of evidence for the practical management of pregnant PKU patient and prediction of phenylalanine tolerance changes during a course of pregnancy.

Case

We report the case of a mother with classical PKU (p.R408W/p.R408W) and the course of her two pregnancies with low phenylalanine tolerance increase (347mg and 227mg) despite the rewarding collaboration with a nutritionist.

Conclusion

This case report does not confirm the observation that a very low phenylalanine tolerance increase in pregnancy of PKU patient is a marker of coexisting PKU-affection in fetus.

Diversity of phenylalanine tolerance in pregnant phenylketonuria patients homozygous for the p.R408W mutation: the need for improved understanding of phenylalanine homeostasis

Dietetic treatment of phenylketonuria (PKU) includes a low-phenylalanine (phe) diet that provides sufficient phe for maintenance and growth plus special phe-free formulas with amino acids to meet requirements for protein, energy and micronutrients.

Weaning practices in phenylketonuria vary between health professionals in Europe

Background

In phenylketonuria (PKU), weaning is considered more challenging when compared to feeding healthy infants. The primary aim of weaning is to gradually replace natural protein from breast milk or standard infant formula with solids containing equivalent phenylalanine (Phe). In addition, a Phe-free second stage L-amino acid supplement is usually recommended from around 6 months to replace Phe-free infant formula. Our aim was to assess different weaning approaches used by health professionals across Europe.

Methods

A cross sectional questionnaire (survey monkey®) composed of 31 multiple and single choice questions was sent to European colleagues caring for inherited metabolic disorders (IMD). Centres were grouped into geographical regions for analysis.

Results

Weaning started at 17–26 weeks in 85% (n = 81/95) of centres, >26 weeks in 12% (n = 11/95) and < 17 weeks in 3% (n = 3/95). Infant's showing an interest in solid foods, and their age, were important determinant factors influencing weaning commencement. 51% (n = 48/95) of centres introduced Phe containing foods at 17–26 weeks and 48% (n = 46/95) at >26 weeks. First solids were mainly low Phe vegetables (59%, n = 56/95) and fruit (34%, n = 32/95).

A Phe exchange system to allocate dietary Phe was used by 52% (n = 49/95) of centres predominantly from Northern and Southern Europe and 48% (n = 46/95) calculated most Phe containing food sources (all centres in Eastern Europe and the majority from Germany and Austria). Some centres used a combination of both methods.

A second stage Phe-free L-amino acid supplement containing a higher protein equivalent was introduced by 41% (n = 39/95) of centres at infant age 26–36 weeks (mainly from Germany, Austria, Northern and Eastern Europe) and 37% (n = 35/95) at infant age > 1y mainly from Southern Europe. 53% (n = 50/95) of centres recommended a second stage Phe-free L-amino acid supplement in a spoonable or semi-solid form.

Conclusions

Weaning strategies vary throughout European PKU centres. There is evidence to suggest that different infant weaning strategies may influence longer term adherence to the PKU diet or acceptance of Phe-free L-amino acid supplements; rendering prospective long-term studies important. It is essential to identify an effective weaning strategy that reduces caregiver burden but is associated with acceptable dietary adherence and optimal infant feeding development.

Early feeding practices in infants with phenylketonuria across Europe

Background

In infants with phenylketonuria (PKU), dietary management is based on lowering and titrating phenylalanine (Phe) intake from breast milk or standard infant formula in combination with a Phe-free infant formula in order to maintain blood Phe levels within target range. Professionals use different methods to feed infants with PKU and our survey aimed to document practices across Europe.

Methods

We sent a cross sectional, survey monkey® questionnaire to European health professionals working in IMD. It contained 31 open and multiple-choice questions. The results were analysed according to different geographical regions.

Results

Ninety-five centres from 21 countries responded. Over 60% of centres commenced diet in infants by age 10 days, with 58% of centres implementing newborn screening by day 3 post birth. At diagnosis, infant hospital admission occurred in 61% of metabolic centres, mainly in Eastern, Western and Southern Europe. Breastfeeding fell sharply following diagnosis with only 30% of women still breast feeding at 6 months.

53% of centres gave pre-measured Phe-free infant formula before each breast feed and 23% alternated breast feeds with Phe-free infant formula. With standard infant formula feeds, measured amounts were followed by Phe-free infant formula to satiety in 37% of centres (n = 35/95), whereas 44% (n = 42/95) advised mixing both formulas together. Weaning commenced between 17 and 26 weeks in 85% centres, ≥26 weeks in 12% and < 17 weeks in 3%.

Discussion

This is the largest European survey completed on PKU infant feeding practices. It is evident that practices varied widely across Europe, and the practicalities of infant feeding in PKU received little focus in the PKU European Guidelines (2017). There are few reports comparing different feeding techniques with blood Phe control, Phe fluctuations and growth. Controlled prospective studies are necessary to assess how different infant feeding practices may influence longer term feeding development.

[Singleton and twin pregnancies of PKU patients - individual variability of phenylalanine tolerance: experience of a single treatment center (Preliminary report)]

Phenylketonuria (PKU) is the autosomal recessive deficiency of phenylalanine hydroxylase resulting in the accumulation of phenylalanine (Phe) in blood and in the brain. Phe restriction in a patient's diet is determined depending on the amount of Phe intake which allows for stable blood Phe levels within the therapeutic range of 120-360µmol/L. In clinical practice the empirical determination of Phe tolerance relies on frequent assessment of blood Phe concentrations in relation to Phe intake from food records. Untreated maternal PKU may lead to maternal PKU syndrome in offspring. The objective of the study was to compare Phe tolerance during the course of singleton and multiple pregnancies of PKU patients. Case subjects and methods: The cases reviewed included three sets of classical PKU-affected Polish women on a low-phenylalanine diet during the course of singleton and twin pregnancies and their PKU-unaffected newborns. All the patients were under regular supervision of a metabolic dietitian to stabilize blood Phe levels and determine Phe tolerance. Data on pregnancy weight gain, the gestational age when the diet initiated, the percent of Phe assessments < 120 µmol/L and > 360 µmol/L, as well as offspring birth measurements were analyzed.

RESULTS

The total increase in Phe tolerance and its pattern during the course of singleton and twin pregnancies differed remarkably in each patient. Three PKU women (Q383X/R408W, EX3DEL/EX3DEL, R281L/R408W) increased their Phe tolerance in singleton and twin pregnancies by 579%/468%, 674%/261%, and 427%/236%, respectively. During the last 10 weeks of singleton and twin pregnancy Phe tolerance showed an increase by 62%/149%, 33%/64%, and 37%/40%, respectively. The analysis of predictors for Phe tolerance showed that an individual's weight gain and the fetal weight gain as estimated from liveborn birth-weight data had no predictive capacity.

CONCLUSIONS

Individual Phe tolerance in singleton pregnancies of PKU patients does not predict tolerance in twin pregnancy. Further research on the growing population of multiple pregnancy PKU patients is necessary to provide evidence-based guidelines to optimize the treatment of PKU in females of childbearing age.

[High plasma folate in patients with phenylketonuria]

Phenylketonuria is an inborn error of metabolism treated with a closely monitored low phenylalanine diet. Protein substitutes used for treatment are supplemented with vitamins and micronutrients.

AIM

The aim of this study was to investigate plasma folic acid concentrations in children with phenylketonuria.

MATERIALS AND METHODS

Retrospective analysis of medical records of 73 patients with phenylketonuria and 28 with mild hyperphenylalaninemia (on normal diet) was carried out. Intake of folic acid was calculated on the basis of protein substitute intake. Folate concentrations were analyzed according to their intake, and concentration of homocysteine and phenylalanine.

RESULTS

In 76.7% patients with phenylketonuria intake of folic acid exceeded recommended dietary allowance. Serum folic acid concentrations above upper reference level were detected in 75.3% patients with phenylketonuria and only in 25% patients with hyperphenylalaninemia (p<0.0001). Strong positive correlation between daily intake of folic acid (with protein substitute) and concentration plasma folic acid (corr=0.55, p<0.0001) has been observed.

CONCLUSIONS

Low phenylalanine diet using protein substitutes currently available in Poland predisposes to high concentration of plasma folic acid. The security of folic acid hipersupplementation in patients with phenylketonuria requires further detailed research.