Maternal PKU: Defining phenylalanine tolerance and its variation during pregnancy, according to genetic background

Benefits of a prolonged-release amino acid mixture in four pregnant women with phenylketonuria

Background: Maternal phenylketonuria (mPKU) is a pathologic condition occurring in the fetus of a mother with PKU that is caused by prolonged elevated intrauterine blood phenylalanine (Phe) levels, which can lead to congenital abnormalities and mental retardation of newborns. Management of PKU during pregnancy can be challenging as protein substitutes may exacerbate nausea, vomiting, and gastrointestinal symptoms. Aim: To report the successful management of four PKU pregnant women. Methods: The patients were administered with prolonged-release amino acid supplementation and were recommended to follow a strict diet. Blood Phe concentration, adherence to diet, and occurrence of adverse events were monitored. Results: All patients achieved safe levels of blood Phe concentration (120-360 µmol/L) since preconception and during pregnancy (mean Phe concentration values of 143.34 ± 137.59, 226.48 ± 194.57, 186.68 ± 133.67, and 187.47 ± 42.59 µmol/L). During the first trimester of pregnancy, all patients manifested gastrointestinal symptoms such as nausea, gastrointestinal reflux, and abdominal bloating, which were managed by either changing protein substitute or extending the time window between different meals and amino acid mixtures administration. The four women continued their pregnancies without experiencing further complications and delivered neonates with normal growth parameters and no malformations. Conclusion: Findings of this case series suggest that the intake of a prolonged-release amino acid mixture in granules is well tolerated by pregnant PKU patients, eventually leading to good metabolic control and fetal growth within normal ranges.

Updating an Overview of Teratology

In this chapter, the authors aim to update an overview of the principles of teratology, beginning with the definition of teratology, the critical point at which this process occurs, and some of the most common etiological agents that improve our understanding of teratology.Modern teratology has greatly improved in recent years with advances in new methods in molecular biology, toxicology, animal laboratory science, and genetics, increasing our knowledge of ambient influences. Nevertheless, there is a lot to do to reduce the influence of hazardous intervening agents, whether they target our genetics or not, that can negatively affect pregnancy and induce congenital development disorders, including morphological, biochemical, or behavioral defects.Certain agents might indeed be related to certain defects, but we have not been able to identify the cause of most congenital defects, which highlights the importance of finding and testing out new genetics techniques and conducting laboratory animal science to unravel the etiology and pathogenicity of each congenital defect.

Phenylketonuria and the brain

Classic phenylketonuria (PKU) is caused by defective activity of phenylalanine hydroxylase (PAH), the enzyme that coverts phenylalanine (Phe) to tyrosine. Toxic accumulation of phenylalanine and its metabolites, left untreated, affects brain development and function depending on the timing of exposure to elevated levels. The specific mechanisms of Phe-induced brain damage are not completely understood, but they correlate to phenylalanine levels and on the stage of brain growth. During fetal life, high levels of phenylalanine such as those seen in maternal PKU can result in microcephaly, neuronal loss and corpus callosum hypoplasia. Elevated phenylalanine levels during the first few years of life can cause acquired microcephaly, severe cognitive impairment and epilepsy, likely due to the impairment of synaptogenesis. During late childhood, elevated phenylalanine can cause alterations in neurological functioning, leading to ADHD, speech delay and mild IQ reduction. In adolescents and adults, executive function and mood are affected, with some of the abnormalities reversed by better control of phenylalanine levels. Altered brain myelination can be present at this stage. In this article, we review the current knowledge about the consequences of high phenylalanine levels in PKU patients and animal models through different stages of brain development and its effect on cognitive, behavioural and neuropsychological function.

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.