Maternal phenylketonuria and phenylalanine restricted diet. Studies of 7 pregnancies and of offsprings produced

Noninherited risk factors and congenital cardiovascular defects: current knowledge: a scientific statement from the American Heart Association Council on Cardiovascular Disease in the Young: endorsed by the American Academy of Pediatrics

Prevention of congenital cardiovascular defects has been hampered by a lack of information about modifiable risk factors for abnormalities in cardiac development. Over the past decade, there have been major breakthroughs in the understanding of inherited causes of congenital heart disease, including the identification of specific genetic abnormalities for some types of malformations. Although relatively less information has been available on noninherited modifiable factors that may have an adverse effect on the fetal heart, there is a growing body of epidemiological literature on this topic. This statement summarizes the currently available literature on potential fetal exposures that might alter risk for cardiovascular defects. Information is summarized for periconceptional multivitamin or folic acid intake, which may reduce the risk of cardiac disease in the fetus, and for additional types of potential exposures that may increase the risk, including maternal illnesses, maternal therapeutic and nontherapeutic drug exposures, environmental exposures, and paternal exposures. Information is highlighted regarding definitive risk factors such as maternal rubella; phenylketonuria; pregestational diabetes; exposure to thalidomide, vitamin A cogeners, or retinoids; and indomethacin tocolysis. Caveats regarding interpretation of possible exposure-outcome relationships from case-control studies are given because this type of study has provided most of the available information. Guidelines for prospective parents that could reduce the likelihood that their child will have a major cardiac malformation are given. Issues related to pregnancy monitoring are discussed. Knowledge gaps and future sources of new information on risk factors are described.

Cognitive development in offspring of untreated and preconceptionally treated maternal phenylketonuria

A survey is given of literature reports on the effect of performance in offspring from 26 maternal PKU pregnancies treated prior to conception. The survey includes two women who were referred to us for genetic counselling because they had both given birth to microcephalic, mentally retarded children. The women were discovered to suffer from unrecognized maternal PKU with fasting phenylalanine concentration of 1.1-1.5 mmol/L. A strict diet was introduced prior to planned pregnancy and after some months on diet (phenylalanine concentrations less than 0.6 mmol/L) they became pregnant again. Serum phenylalanine levels were monitored weekly throughout pregnancy, and adjustments in the diet were made to keep serum phenylalanine concentration within the range of 0.18-0.42 mmol/L. The outcome of the pregnancies were healthy children who have developed normally. Their IQs are 105 and 119 at ten and four years of age, respectively and their head circumferences are normal. Our data show that the effect of preconceptional dietary treatment was children with a normal performance, contrary to their older siblings born following untreated pregnancies. These results are in agreement with the survey of ten years' promising experiences with preconceptional treatment in maternal PKU. The data may help to motivate young PKU women to accept planned pregnancies and to encourage them to return to the strict diet, which has prevented them from being retarded.

Newborn screening for hyperphenylalaninemia on day 5: is 240 mumol/liter the most appropriate cut-off level?

In most countries, including the UK, Sweden, Japan, and the FRG, blood samples for newborn screening are not taken until Day 5, in contrast to Day 3 in the United States. This results in fundamentally different conditions with respect to the amount of phenylalanine ingested by the newborn until the day of sampling. Nevertheless those countries who routinely screen on Day 5 have adopted the U.S. cut-off level of 240 mumol/liter (4 mg/dl). This study is the first to compare, via direct evaluation of a regional screening program, whether a higher or a lower cut-off level would be more appropriate for phenylalanine screening on Day 5. In a prospective study on phenylalanine screening with 132,638 infants (cut-off level 120 mumol/liter) the number of recalls was 152. Among them 14 cases with a permanent disorder of phenylalanine metabolism were detected. With the officially recommended cut-off level of 240 mumol/liter as well as with the 360 mumol/liter level used in some centers, the recall rate would have been lower, specificity higher, and the predictive values of a positive result higher. On the other hand sensitivity would have been significantly lower (only 80%). Because in newborn screening the crucial point is sensitivity, our data suggest that in phenylalanine screening done on Day 5 cut-off levels of 240 or 360 mumol/liter are less appropriate than a lower cut-off level. With higher cut-off levels a large proportion of patients (one-fifth) with a permanent disorder of phenylalanine metabolism would be missed.

Maternal phenylketonuria--the Irish experience

The outcome of 48 pregnancies in 18 women with elevated phenylalanine was studied. The women were divided into two groups, diet and non-diet. All the women on diet had severe hyperphenylalaninaemia and only six were on the amino acid mixture at conception. In the non-diet group four women had concentrations of less than 1000 mumols/L and five had severe hyperphenylalaninaemia. Three deaths and one stillbirth occurred in the non-diet group. Microcephaly occurred in 24 children; 11 in the diet group and 13 in the non-diet group. There were five miscarriages in the non-diet group and one in the diet group. Diet is beneficial when started early but planned pregnancies, good motivation and compliance were difficult to achieve in this group of women despite every reasonable effort by the PKU clinic.

Maternal phenylketonuria and hyperphenylalaninemia: implications for medical practice in the United States

The risk of maternal phenylketonuria and hyperphenylalaninemia syndrome, a preventable cause of severe birth defects and retardation with a near 100% recurrence risk if untreated, is increasing in the United States. The reasons for this are reviewed. Women with hyperphenylalaninemia and those with phenylketonuria diagnosed and treated at birth are intellectually normal, as are some women with undiagnosed phenylketonuria. Both groups are at risk for maternal phenylketonuria syndrome in their offspring if blood phenylalanine levels are not controlled by diet during pregnancy. The problems and pitfalls of suspecting, diagnosing, and managing the condition are discussed. Suggested strategies for reversing the increasing trend include the greater use of genetic registers, increased clinical awareness, and some form of rescreening. The advantages and costs of rescreening a subset of pregnant women or all pregnant women at or before their first registration are examined.

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.

Pre-conceptual dietary management for maternal phenylketonuria

Experience of preconceptual dietary management of maternal hyperphenylalaninaemia is limited. Two Edinburgh mothers with hyperphenylalaninaemia and borderline IQ have received dietary advice to maintain normal plasma Phe concentration both before conception and during pregnancy, in an attempt to prevent foetal abnormality. Satisfactory compliance was only obtained after intensive in-patient instruction and the diets were maintained for long periods prior to conception. Intellectual and psychological factors were very important and the availability of "same day" biochemical reports useful in encouraging the mothers. Both infants have normal Phe concentrations and satisfactory growth and development parameters at present. Further follow-up continues but these cases provide further evidence in favour of the use of preconceptual dietary advice in the management of maternal hyperphenylalaninaemia.