Outcome of pregnancy in the rat with mild hyperphenylalaninaemia and hypertyrosinaemia: implications for the management of "human maternal PKU"

L-tyrosine supplementation does not ameliorate skeletal muscle dysfunction in zebrafish and mouse models of dominant skeletal muscle α-actin nemaline myopathy

L-tyrosine supplementation may provide benefit to nemaline myopathy (NM) patients, however previous studies are inconclusive, with no elevation of L-tyrosine levels in blood or tissue reported. We evaluated the ability of L-tyrosine treatments to improve skeletal muscle function in all three published animal models of NM caused by dominant skeletal muscle α-actin (ACTA1) mutations. Highest safe L-tyrosine concentrations were determined for dosing water and feed of wildtype zebrafish and mice respectively. NM TgACTA1^D286G-eGFP zebrafish treated with 10 μM L-tyrosine from 24 hours to 6 days post fertilization displayed no improvement in swimming distance. NM TgACTA1^D286G mice consuming 2% L-tyrosine supplemented feed from preconception had significant elevations in free L-tyrosine levels in sera (57%) and quadriceps muscle (45%) when examined at 6–7 weeks old. However indicators of skeletal muscle integrity (voluntary exercise, bodyweight, rotarod performance) were not improved. Additionally no benefit on the mechanical properties, energy metabolism, or atrophy of skeletal muscles of 6–7 month old TgACTA1^D286G and KIActa1^H40Y mice eventuated from consuming a 2% L-tyrosine supplemented diet for 4 weeks. Therefore this study yields important information on aspects of the clinical utility of L-tyrosine for ACTA1 NM.

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.

Maternal and fetal tyrosinemia type I

A 22 year-old woman with tyrosinemia type I (HT1) married her first cousin who is heterozygous for the same FAH mutation for which the patient is homozygous. During her pregnancy she was treated with diet (prescribed tyrosine intake 300 mg/day), and nitisinone (60 mg/day). Median plasma tyrosine levels were 560 μmol/L (range: 375-838, n = 21) and nitisinone 51 μmol/L (range: 41-57, n = 3) during pregnancy. She gave birth to a clinically healthy girl affected with tyrosinemia type 1. Birth was normal (birth weight 2615 g) and the baby had normal liver function, normal plasma alpha-fetoprotein concentrations, low urinary excretion of phenolic acids and no detectable succinylacetone. At birth, the baby had hypertyrosinemia (860 μmol/L in blood cord) and nitisinone levels of 14 μmol/L. Following molecular confirmation of the diagnosis of HT1 specific treatment began on day 15 by which time she had detectable urinary succinylacetone.

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.

Maternal tyrosinaemia II: management and successful outcome

A 25-year-old woman with tyrosinaemia type II was treated from the 5th week of pregnancy with a protein-restricted diet supplemented with a tyrosine/phenylalanine-free amino acid mixture. Tyrosine concentrations were maintained in the range 100-200 mumol/l by restricting natural protein intake to 0.16 g/kg per 24 h in early pregnancy, with increases up to 0.38 g/kg per 24 h in the last trimester. This treatment maintained plasma phenylalanine concentrations in the range 20-40 mumol/l. Maternal weight gain and fetal growth were normal, and the mother remained asymptomatic throughout the pregnancy. A normal infant was born at term with length, weight and head circumference between the 25-50th per centiles.

Pregnancy in phenylketonuria: dietary treatment aimed at normalising maternal plasma phenylalanine concentration

The transport characteristics of the placenta, which favour higher phenylalanine concentrations in the fetus than in the mother, and regression data of head circumference at birth against phenylalanine concentration at conception in maternal phenylketonuria (PKU), suggest that treatment of maternal PKU should ideally aim to maintain plasma phenylalanine concentration within the normal range throughout pregnancy. A patient with classical PKU was treated from before conception by aiming to maintain plasma phenylalanine concentration within the range 50-150 mumol/l and tyrosine within the range 60-90 mumol/l. The diet was supplemented with phenylalanine-free amino acids (100-180 g/day) and tyrosine (0-5 g/day). Plasma amino acid concentrations were monitored weekly by amino acid analyser. Dietary phenylalanine intake ranged from 6 mg/kg/day at conception to 30 mg/kg/day at delivery. Normal weight gain and fetal growth were maintained throughout the pregnancy. A normal baby was born at term with a head circumference of 35.5 cm; at 1 year of age no abnormality is detectable. These results show that with careful monitoring and compliance it is possible, and may be advisable, to maintain plasma phenylalanine concentration within the normal range in the management of PKU pregnancy.

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.

Reduced myelinogenesis and recovery in hyperphenylalaninemic rats. Correlation between brain phenylalanine levels, characteristic brain enzymes for myelination, and brain development

In a previous paper (Burri et al., 1990), we have shown that experimental hyperphenylalaninemia (hyper-Phe) in 3-17 d-old rats leads to reduced myelinogenesis. Such treated rats recover during a 6 w low phenylalanine (Phe) period between days 17 and 59. In order to get more detailed information about the disturbed myelinogenesis and recovery, we measured in hyper-Phe rats the developmental pattern of two brain enzymes typical for myelination, cerebroside sulfotransferase (CST), and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP), and other developmental parameters. Further, we correlated brain Phe levels with the brain damage in hyper-Phe rats, and we measured brain acetylcholinesterase (AChE) as a neuronal marker. Experimental hyper-Phe rats, injected between postnatal days 3 and 17 with alpha-methylphenylalanine and phenylalanine, showed a delayed age-dependent increase of CST activity, compared to that of controls. In hyper-Phe rats, CST peak activity was reached 2-4 d later, and was lower than in controls. The age-dependent decrease of the CST activity, however, started in test and control rats at the same time, at day 21. Between days 24 and 59, hyper-Phe rats had normal CST activity. CNP activity in hyper-Phe rats was lower than in controls from day 10 to 35, and recovered to normal values between days 35 and 59. Our results indicate that recovery from reduced myelinogenesis is possible after the period of fast myelination without compensatory increased CST activity. Further, the brain damage in test rats with Phe levels higher than average is more severe than in test rats with Phe levels lower than average; and there is no effect of hyperphenylalaninemia on brain neurons containing AChE.

Maternal phenylketonuria (PKU)--a review

This review points out the very high incidence of damage to the fetus in untreated maternal phenylketonuria (PKU). In classical cases, 92% of the offspring are mentally retarded, 73% have microcephaly, 40% are growth retarded at birth, and 12% have congenital anomalies. Less severe types of PKU and its variants and patients treated with a low phenylalanine diet during pregnancy have a much lower incidence of these defects in their offspring. Very promising results have been obtained in a small number of preconception and early first trimester treated patients under very strict dietary control. Nutrition of the mother and fetus is a major concern during the application of this restrictive diet and must be monitored closely to avoid fetal damage from malnutrition. A 7-year collaborative study of maternal PKU began in November 1984 in the US and Canada, but even in this well publicized study, many patients are presenting late for treatment. It is suggested that premarital and/or prenatal screening for maternal PKU should be initiated for the next generation.