Maternal phenylketonuria

Maternal genetic disorders and fetal development

With improvements in early diagnosis and management of genetic diseases, more women with genetic disorders are reaching reproductive age and becoming pregnant. While pregnancy can have a significant impact on a woman's health when there is an underlying genetic disorder, there can also be fetal effects, including embryopathy, fetal growth restriction, and brain injury. Some maternal genetic disorders are associated with adverse perinatal outcomes, including a high risk of perinatal loss and preterm birth. In this article, we review several maternal genetic disorders associated with fetal risk that are important for clinicians and patients to understand and manage appropriately. These include phenylalanine hydroxylase (PAH) deficiency and other inborn errors of metabolism, tuberous sclerosis complex, myotonic dystrophy, cystic fibrosis, Turner syndrome, sickle cell disease, and connective tissue disorders.

The complete European guidelines on phenylketonuria: diagnosis and treatment

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism caused by deficiency in the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. If left untreated, PKU results in increased phenylalanine concentrations in blood and brain, which cause severe intellectual disability, epilepsy and behavioural problems. PKU management differs widely across Europe and therefore these guidelines have been developed aiming to optimize and standardize PKU care. Professionals from 10 different European countries developed the guidelines according to the AGREE (Appraisal of Guidelines for Research and Evaluation) method. Literature search, critical appraisal and evidence grading were conducted according to the SIGN (Scottish Intercollegiate Guidelines Network) method. The Delphi-method was used when there was no or little evidence available. External consultants reviewed the guidelines. Using these methods 70 statements were formulated based on the highest quality evidence available. The level of evidence of most recommendations is C or D. Although study designs and patient numbers are sub-optimal, many statements are convincing, important and relevant. In addition, knowledge gaps are identified which require further research in order to direct better care for the future.

Phenylketonuria: tyrosine supplementation in phenylalanine-restricted diets

Treatment of phenylketonuria (PKU) consists of restriction of natural protein and provision of a protein substitute that lacks phenylalanine but is enriched in tyrosine. Large and unexplained differences exist, however, in the tyrosine enrichment of the protein substitutes. Furthermore, some investigators advise providing extra free tyrosine in addition to the tyrosine-enriched protein substitute, especially in the treatment of maternal PKU. In this article, we discuss tyrosine concentrations in blood during low-phenylalanine, tyrosine-enriched diets and the implications of these blood tyrosine concentrations for supplementation with tyrosine. We conclude that the present method of tyrosine supplementation during the day is far from optimal because it does not prevent low blood tyrosine concentrations, especially after an overnight fast, and may result in largely increased blood tyrosine concentrations during the rest of the day. Both high tyrosine enrichment of protein substitutes and extra free tyrosine supplementation may not be as safe as considered at present, especially to the fetus of a woman with PKU. The development of dietary compounds that release tyrosine more slowly could be beneficial. We advocate decreasing the tyrosine content of protein substitutes to approximately 6% by wt (6 g/100 g protein equivalent) at most and not giving extra free tyrosine without knowing the diurnal variations in the blood tyrosine concentration and having biochemical evidence of a tyrosine deficiency. We further advocate that a better daily distribution of the protein substitute be achieved by improving the palatability of these products.

The international study of pregnancy outcome in women with maternal phenylketonuria: report of a 12-year study

OBJECTIVE

The purpose of this report was to update the results of the Maternal Phenylketonuria Collaborative Study, which was established to assess the efficacy of a phenylalanine-restricted diet in preventing morbidity among the offspring of women with hyperphenylalaninemia.

STUDY DESIGN

During a 12-year period 576 women with hyperphenylalaninemia were enrolled in this study. Outcome measures were stratified according to classification of maternal hyperphenylalaninemia and the time at which dietary control of phenylalanine level was achieved.

RESULTS

Optimal physical and cognitive fetal outcomes occurred when maternal blood phenylalanine level <600 micromol/L was achieved by 8 to 10 weeks' gestation and maintained throughout pregnancy (trimester average, </=600 micromol/L).

CONCLUSIONS

The achievement of blood phenylalanine level control through a phenylalanine-restricted diet significantly diminished the occurrence of congenital abnormalities among offspring of women with hyperphenylalaninemia and improved early intellectual progress of these offspring.

Gestational carrier--a reproductive haven for offspring of mothers with phenylketonuria (PKU): an alternative therapy for maternal PKU

Maternal phenylketonuria, PKU, has a detrimental effect on embryogenesis. Infant pathology is independent of fetal genotype, but is directly correlated with excessive phenylalaninaemia throughout pregnancy. Although normal children have been delivered by affected mothers who either had benign hyperphenylalaninaemia or in whom strict diet has apparently maintained maternal phenylalaninaemia in the low normal range from before conception, more abnormal than normal births have been reported. In addition, attempts at dietary management are often unsuccessful; most reported cases documented various severe pathological consequences of maternal PKU. Currently available methods provide viable alternative treatment. In vitro fertilization using the parental gametes, followed by implantation of the pre-embryo in a surrogate mother, would avoid a metabolic environment impairing normal development, and therefore should be recommended as alternative therapy for potential mothers with PKU.

Nurses' role in preventing birth defects in offspring of women with phenylketonuria

Most women who began nutrition support as neonates for a diagnosis of phenylketonuria, an inherited defect in phenylalanine metabolism, are of normal intelligence, no longer require a restricted diet, and wish to have children of their own. Phenylketonuria that is untreated when a woman conceives and during gestation results in poor reproductive outcomes. Treatment with and careful monitoring of a phenylalanine-restricted diet can improve reproductive outcome. Nurses have the primary responsibility in locating women of childbearing age with phenylketonuria; developing strategies to improve palatability of the diet, thereby enhancing compliance; providing ongoing monitoring and support of the mother-child dyad; and counseling couples at risk.

Management of inborn errors of metabolism during pregnancy

An increasing number of women with inherited metabolic disorders survive, conceive and have children. In order to safeguard the health of the mother and the developing embryo, fetus, and newborn during pregnancy, delivery, and the neonatal period it is necessary to be aware of the range of metabolic disorders, the risks to mothers and children, and appropriate management strategies. The roles of the Paediatrician, Obstetrician and Dietitian in the management of Maternal Hyperphenylalaninaemia and phenylketonuria are reviewed.

A preliminary report of the collaborative study of maternal phenylketonuria in the United States and Canada

The Maternal Phenylketonuria Collaborative Study (MPKUCS), encompassing all the United States and provinces of Canada, is a prospective, longitudinal investigation designed to ascertain the efficacy of phenylalanine-restricted therapy in protecting the fetus from high maternal phenylalanine concentrations in women with hyperphenylalaninaemia. Preliminary findings are reported for 147 pregnancies for whom the recommended therapeutic range of blood phenylalanine was 120-360 mumols/L. Sixty-three pregnancies had complete data for analysis. Dietary control was attempted prior to conception in 10 out of 63 women. Significant negative correlations were noted in length, weight and head circumference and blood phenylalanine concentrations during pregnancy. Average reported phenylalanine levels by trimester for 63 hyperphenylalaninaemic pregnancies resulting in live births revealed that no group requiring treatment achieved levels below 360 mumols/L until the third trimester. Median birth measurement percentiles revealed that all groups studied generally had smaller head size compared with birth length and weight. Those started on diet after the first trimester achieved a head circumference below the 10th percentile. The implication of small head circumference for subsequent intellectual development is unclear at this time. Furthermore, the study must evaluate more offspring of women having optimal preconception and pregnancy restriction of phenylalanine.

Maternal phenylketonuria: successful outcome in four pregnancies treated prior to conception

The management of four pregnancies in two phenylketonuric women is described. A successful outcome in these pregnancies is ascribed to the initiation of treatment prior to conception and the maintenance of tight control with serum phenylalanine between 100 and 400 mumol/l throughout the gestation period. A trial of diet is desirable before a decision is made about pregnancy and before contraception is ceased. Close contact must be maintained with female phenylketonurics throughout their reproductive life to ensure that this process is followed.

The effects of fetal energy depletion on amniotic fluid concentrations of amino acids, organic acids and related metabolites

Concentrations of amino and organic acids, phosphate, sulphate, gluconic acid and gluconolactone were measured in amniotic fluid samples which contained either normal or raised hypoxanthine concentrations. In this way, the effect of mild fetal ATP depletion could be determined. The effects of this mild asphyxia were to raise concentrations of phenylalanine, tyrosine, lysine, glycine, phosphate, sulphate, gluconic acid and glucono-1,5-lactone. However, concentrations of a variety of other metabolites were unchanged; thus no diagnostic confusion should arise with organic acidurias in mild asphyxia in contrast to the biochemical mimickry produced by severe asphyxia. Since clinically normal parturition can produce changes in amniotic fluid, urine from newborn or cord blood may not reflect the metabolic balance in utero.