Disruption of cholesterol homeostasis in the developing brain as a potential mechanism contributing to the developmental neurotoxicity of ethanol: an hypothesis

While excess cholesterol may have deleterious consequences, as in the case of atherosclerosis, too little cholesterol may endanger the development of the brain. Different degrees of mental retardation are often observed in inborn errors of cholesterol synthesis, such as the Smith-Lemli-Opitz syndrome or in maternal phenylketonuria, where the metabolite of accumulating phenylalanine, phenylacetate, is an inhibitor of cholesterol synthesis. Lack of cholesterol during brain development as a consequence of these genetic defects leads to severe brain damage, microencephaly and mental retardation, which are also hallmarks of the fetal alcohol syndrome (FAS). The brain relies on the in situ synthesis of cholesterol, which occurs mostly in astrocytes. Astrocyte-produced cholesterol is utilized for cell proliferation, or is released, via astrocyte-secreted high density lipoprotein-like particles containing apolipoprotein E, outside the cell, where it is taken up and utilized by neurons for dendrite outgrowth and to form synapses. We propose the hypothesis that ethanol may disrupt cholesterol homeostasis during brain development, and that this effect may be responsible, at least in part, for the central nervous system dysfunctions observed in the FAS, which include altered astrocyte proliferation, neuronal death and diminished synaptic contacts.

Effect of high maternal blood phenylalanine on offspring congenital anomalies and developmental outcome at ages 4 and 6 years: the importance of strict dietary control preconception and throughout pregnancy

OBJECTIVES

The Maternal Phenylketonuria Study was designed to determine the effect of a phenylalanine (Phe)-restricted diet in reducing the morbidity on the fetus. Congenital abnormalities were noted, with the focus on the effect of congenital heart defects (CHDs) and microcephaly (MICRO) on developmental outcome at 4 and 6 years of age.

STUDY DESIGN

Women with blood Phe levels >240 micromol/L (n=526; to convert micromol/L to mg/dL, divide by 60) were enrolled; 382 contributed 572 pregnancies. The women had 413 offspring examined at birth and annually. At 4 years, the McCarthy General Cognitive Index was administered, and at 6 years, the Wechsler Intelligence Scale for Children Revised was administered.

RESULTS

Microcephaly was noted in 137 (33%) of the offspring, and 32 (7.7%) had CHD. Maternal blood Phe levels were higher for infants with CHD and MICRO than for infants with CHD only (P=.02). Mean Phe levels at 4 to 8 weeks gestation predicted CHD (P<.0001). The McCarthy General Cognitive Index score was lower with CHD (P=.005) and MICRO (P=.0017), as was the Wechsler Intelligence Scale for Children Revised full-scale IQ score (P=.0002 for CHD and P=.0001 for MICRO). None of the subjects who had offspring with CHD had Phe control between 120 and 360 micromol/L during the first 8 to 10 weeks of gestation.

CONCLUSIONS

Women with phenylketonuria need to be educated regarding diet for life. This should help improve diet control before conception and throughout pregnancy.

The National Institute of Child Health and Human Development and phenylketonuria

The National Institute of Child Health and Human Development (NICHD) was established shortly after the Guthrie test for screening newborn infants for phenylketonuria (PKU) was introduced. The NICHD supported the study demonstrating the long-term efficacy of screening and a low-phenylalanine diet in preventing mental retardation. With the identification of the adverse impact on fetal development of high intrauterine phenylalanine exposure from a mother with PKU, the NICHD organized and supported the study reported here, demonstrating the protective effect of phenylalanine restriction of the mother's diet during pregnancy. The study provides clear guidance for the management of pregnancy in women with PKU.

Relation of prenatal phenylalanine exposure to infant and childhood cognitive outcomes: results from the International Maternal PKU Collaborative Study

OBJECTIVE

The primary aims of this study were to model the form of the relation between prenatal exposure to phenylalanine (Phe) and measures of offspring intellectual development and to estimate the developmental relations of maternal demographic, pregnancy-related, and perinatal variables on offspring intelligence during infancy and childhood.

METHODS

The participants were the 413 children and their mothers from the International Maternal PKU Collaborative Study.

RESULTS

Results supported a nonlinear relation between prenatal Phe exposure and offspring cognitive outcomes, with damage to the developing fetus if average Phe levels are above approximately 360 micromol/L. Moreover, prenatal Phe exposure had a strong effect on offspring outcomes at 1 year of age and was the only one of the background, pregnancy-related, or perinatal variables to influence directly offspring outcomes at 2, 4, and 7 years of age.

CONCLUSION

The present study was able to document the importance of prenatal exposure to Phe for predicting offspring cognitive outcomes in the presence of other predictors of these outcomes.

The Maternal Phenylketonuria Project: a summary of progress and challenges for the future

The results of the International Collaborative Study of Maternal phenylketonuria have shown that dietary phenylalanine restriction of women with hyperphenylalaninemia during pregnancy decreases the incidence of mental retardation, microcephaly, congenital heart disease, and intrauterine growth retardation in their offspring. The best results are achieved when treatment is initiated before conception. Psychosocial problems are the most pervasive obstacle to the achievement of optimum dietary treatment. Novel, nondietary approaches to the treatment of maternal phenylketonuria are under development.

Cognitive and behavioral development in maternal phenylketonuria offspring

OBJECTIVE

To assess cognitive and behavioral outcome in treated maternal phenylketonuria (PKU) offspring.

METHODS

In this prospective, longitudinal study, 228 children who were born to mothers with treated PKU or untreated mild hyperphenylalaninemia were compared with 70 control subjects at 7 years of age.

RESULTS

Offspring cognitive outcome negatively correlated with the number of gestational weeks that elapsed until maternal metabolic control was achieved (r = -0.61). Behavioral outcome was similarly affected. Postnatal measurement of stimulation in the home was also related to offspring IQ.

CONCLUSIONS

Children who are born to mothers who have PKU and attain metabolic control before or very early in pregnancy seem to begin life with undiminished potential. Delay in attainment of maternal metabolic control is associated with declines in offspring developmental outcome. The postnatal environment also significantly affects outcome. Interventions to improve dietary compliance before and throughout pregnancy as well as interventions to improve the postnatal home environment may reduce the risks associated with maternal PKU.

Historical background for the maternal PKU syndrome

OBJECTIVE

To provide information on the history of maternal phenylketonuria.

METHODS

A review of the literature and personal observations were conducted.

RESULTS

Compilation of sequential information about the development of our understanding of maternal PKU was produced.

CONCLUSIONS

The history of maternal PKU reflects continuous additions to our understanding of this teratogenic syndrome.

Developmental neurotoxicity: do similar phenotypes indicate a common mode of action? A comparison of fetal alcohol syndrome, toluene embryopathy and maternal phenylketonuria

Developmental neurotoxicity can be ascribed to in utero exposure to exogenous substances or to exposure of the fetus to endogenous compounds that accumulate because of genetic mutations. One of the best recognized human neuroteratogens is ethanol. The Fetal Alcohol Syndrome (FAS) is characterized by growth deficiency, particular facial features, and central nervous system (CNS) dysfunctions (mental retardation, microencephaly and brain malformations). Abuse of toluene by pregnant women can lead to an embryopathy (fetal solvent syndrome, (FSS)) whose characteristics are similar to FAS. Phenylketonuria (PKU) is a genetic defect in phenylalanine (Phe) metabolism. Offspring of phenylketonuric mothers not under strict dietary control are born with maternal PKU (mPKU), a syndrome with similar characteristics as FAS and FSS. While ethanol has been shown to cause neuronal death, no such evidence is available for toluene or Phe and/or its metabolites. On the other hand, alterations in astrocyte proliferation and maturation have been found, mostly in in vitro studies, which may represent a potential common mode of action for at least some of the CNS effects found in FAS, mPKU, and FSS. Further in vivo and in vitro studies should validate this hypothesis and elucidate possible molecular targets.

[Maternal phenylketonuria]

The child of a phenylketonuric woman is exposed during pregnancy to a high risk of growth retardation and malformation. The frequency of these abnormalities is proportional to the maternal phenylalanine blood concentrations. If a strict low protein diet is followed before conception and throughout gestation the risks of abnormalities are not higher than in the normal population. The maternal blood phenylalanine levels must be maintained between 120 and 250 mumol/l and the tyrosine blood levels between 45 and 90 mumol/l. Weekly blood analyses are mandatory. Regular dietary controls are necessary to assure that the adequate energetic intake and the correct amounts of vitamins and minerals recommended for a pregnant woman are sustained. A case report is the opportunity to discuss certain practical aspects concerning the monitoring of the pregnancy of a phenylketonuric woman and to make general recommendations.

Effect of phenylalanine and its metabolites on the proliferation and viability of neuronal and astroglial cells: possible relevance in maternal phenylketonuria

Phenylketonuria is a genetic defect that, without strict dietary control, results in the accumulation of phenylalanine (Phe) in body fluids. If a low-Phe diet is not maintained during pregnancy, the offspring of phenylketonuric women are born with mental retardation and microcephaly. Primary cultures of rat cerebellar granule cells, rat cortical astrocytes, human fetal astrocytes, and human neuroblastoma (SY5Y) cells and human astrocytoma (1321N1) cells were used to test the hypothesis that the microencephaly may be a result of neuronal cell death and reduced astrocyte proliferation. Exposure to Phe or to six Phe metabolites [phenylacetic acid (PAA), phenyllactic acid, hydroxyphenylacetic acid, phenylpyruvic acid, phenylethylamine (PEA), and mandelic acid] did not result in astroglial or neuronal cell cytotoxicity. Treatment of 1321N1 cells, human fetal astrocytes, or rat astrocytes with 5 mM Phe for 24 h decreased DNA synthesis 19 +/- 4, 30 +/- 4, and 60 +/- 6%, respectively. This effect was concentration dependent, and flow cytometry revealed that Phe treatment resulted in the accumulation of cells in the G(0)/G(1) phase of the cell cycle. In addition, in 1321N1 cells, exposure to 5 mM PAA, and in rat astrocytes, exposure to 0.5 mM PEA inhibited cell proliferation 42 +/- 4 and 55 +/- 4%, respectively. These metabolites also resulted in the accumulation of cells in the G(0)/G(1) phase of the cell cycle. In human fetal astrocytes, 0.5 mM PEA and 0.5 mM PAA resulted in a 41 +/- 12 and 52 +/- 11% reduction proliferation, respectively.

The International Collaborative Study of Maternal Phenylketonuria: status report 1998

The Maternal Phenylketonuria Study began in 1984 and during the intervening years, 572 pregnancies in hyperphenylalaninemic women and 99 controls and their outcomes have been evaluated. Among hyperphenylalaninemic women who delivered a live infant, only 15.9% were treated and in metabolic control preconceptually, however, another 18.4% were in control by 10 weeks. Compared to the results reported by Lenke and Levy in 1980, there is a marked improvement in outcome with treatment. Microcephaly was unusual in preconceptually treated pregnancies with well controlled phenylalanine restricted diets. Even in pregnancies that established control after conception but before the 8th week, congenital heart disease did not occur in the offspring, however, it did occur in 12% of pregnancies not achieving control until after 10 weeks of pregnancy.

CONCLUSION

The recommended level of blood phenylalanine during pregnancy is 120-360 mumol/l. Best results were obtained by close cooperation between the attending obstetrician and a metabolic team experienced in the care of persons with phenylketonuria.

[Phenylketonuria: a children's disease in adulthood]

The prognosis for patients with phenylketonuria (PKU) has improved greatly with early institution of treatment after birth. It was assumed that the diet could be terminated after adolescence but there are strong indications that hyperphenylalaninaemia can have detrimental effects in adult patients. Hyperphenylalaninaemia can cause reversible white matter abnormalities, and is also associated with psychiatric illness, which improves with lowering of the plasma phenylalanine level. Even optimally treated patients generally have a decreased performance with neuropsychological tests compared with subjects without PKU. Elevation of the plasma phenylalanine level leads to worsening of neuropsychological performance, lowering of the level leads to improved performance. Strict metabolic control is necessary during pregnancy in women with PKU in view of the increasing frequency of congenital abnormalities with increasing phenylalanine level. The complexity and demanding nature of the diet treatment make specialised facilities for optimal medical and paramedical care mandatory.

[Embryonic pathology caused by maternal phenylketonuria. A cause of underdiagnosed mental retardation. A report of 8 cases]

OBJECTIVE

Maternal phenylketonuria (MPKU) is characterized by intrauterine growth retardation, microcephaly, congenital malformations (mainly cardiac defects), dysmorphic facial features and mental retardation. There are women of child-bearing age that do not know that they are affected by phenylketonuria (PKU) and their pregnancies could result in damage to the fetus expressed as different neurological and congenital abnormalities.

PATIENTS AND METHODS

We report 8 patients from 4 families. The first family had two offspring with intrauterine growth retardation, microcephaly and psychomotor retardation. The second family consisted of a daughter with mental retardation (without further data), a second baby which died during the first day of life, and a third child which died at 7 months of age with cardiac defects, microcephaly and dysmorphic features. Another child had intrauterine growth retardation, microcephaly psychomotor retardation, dysmorphic features and cardiac defects (coarctation of the aorta and subaortic stenosis). The third family had a son with microcephaly and mental retardation. The fourth family had a boy that died at 3 weeks of age with microcephaly, dysmorphic facial features, congenital heart disease (mitral atresia and septal defects) and Meckel diverticulum and a girl 5 years of age with intrauterine growth retardation, microcephaly and mental retardation. In all cases the mothers were unaware that they were affected by PKU and had mild intellectual defects. Two of them had PKU phenotypes.

CONCLUSIONS

The offspring of PKU mothers untreated during pregnancy are affected by characteristic embriopathies related to the level of phenylalanine during pregnancy. In Spain, massive routine newborn screening was introduced around 1980-1985 and at present there are women of child-bearing age and are unaware that they are affected by the disease and that their pregnancies may result in fetal damage, as we demonstrate in these 8 patients. When faced with women with mental handicap or with antecedents of offspring with mental retardation, cardiac defects, microcephaly or intrauterine growth retardation, the determination of maternal phenylalanine concentrations is recommended. These teratogenic pathologies tend to disappear, but for the moment it is necessary to prevent this teratogenicity. The diagnosis is easy, avoids complementary exams, may help family studies and allows the implementation of dietary restriction during the subsequent pregnancy that would prevent fetal damage.

[Pregnancy and the child of a mother with phenylketonuria]

Pregnant women with hyperphenylalaninemia are at high risk of spontaneous abortion and of giving birth to infants with congenital malformations, microcephaly and mental defect. Among mothers whose phenylalaninemia is greater than 1200 mumol/L (20 mg/100 mL), 95% have at least one child with mental retardation. A low phenylalanine diet with a good control of phenylalaninemia, started before conception, reduces this risk, better results being obtained when plasma phenylalanine levels are maintained below 360 mumol/L (6 mg/100 mL) as compared with levels maintained between 360 to 600 mumol/L (6-10 mg/100 mL). Thus, systematic contraception and planned pregnancies must be recommended in all hyperphenylalanemic young women. This implies early information of phenylketonuric teenage girls and their parents. In addition, efforts must be made to join and inform all women having had hyperphenylalaninemia at birth, whether they received a dietary treatment or not. It is also important that general practitioners, pediatricians and obstetricians be aware of the high recurrence risk in hyperphenylalanemic women who gave birth to a microcephalic or malformed infant.

MRI characterization of cerebral dysgenesis in maternal PKU

MPKU pregnancies, with or without dietary treatment to reduce maternal plasma phenylalanine (phe), show variable, increased non-physiologic levels, as the putative cause of fetal teratogenicity. Cerebral dysgenesis with clinical neonatal microcephaly and congenital heart disease indicates altered organ morphogenesis. Although there is not an established precise relationship between maternal phe levels and outcome, dietary restriction before or early in gestation is universally advised. Both human experience and animal research have suggested differential organ responses to high and low phe levels. Structural microencephaly may be due to reduced brain volume or abnormal regional brain development. Infants in MPKU are also at risk to develop PKU. Microencephaly was evident by MRI in 8 of 21 infants born to 12 MPKU mothers; 2 infants of one mother developed PKU. All levels of gestational plasma phe were associated with otherwise structurally normal infant microencephalic brains appropriate for age in myelination. CHD occurred in one microencephalic infant of a classic MPKU treated in the first trimester. Maternal, cord and neonatal plasma phenylalanine at delivery did not correlate with teratogenic effects. Only untreated 'classic' MPKU fetal effects appear predictable.

The international collaborative study of maternal phenylketonuria: status report 1994

Neonatal screening for phenylketonuria (PKU) has created a problem as females with PKU are reaching child-bearing age. Surveys have revealed that maternal phenylalanine blood concentrations greater than 1200 mumol/l are associated with fetal microcephaly, congenital heart defects and intrauterine growth retardation. It is estimated that as many as 3000 hyperphenylalaninemic females may be at risk of producing these fetal abnormalities. To examine this problem, the international maternal PKU collaborative study was developed to evaluate the efficacy of a phenylalanine-restricted diet in reducing fetal morbidity. Preliminary findings have indicated that phenylalanine restriction should begin before conception for females with PKU planning a pregnancy. Dietary control should maintain maternal blood phenylalanine levels between 120 and 360 mumol/l and should provide adequate energy, protein, vitamin and mineral intake. Pregnant hyperphenylalaninemic females who achieved metabolic control after conception or by the 10th week of pregnancy had a better offspring outcome than anticipated. The results of 402 pregnancies are reviewed.

Phenylketonuria due to phenylalanine hydroxylase deficiency: an unfolding story. Medical Research Council Working Party on Phenylketonuria

Efficient neonatal screening for phenylketonuria and the availability of complex diets for lifelong use have virtually eliminated severe mental handicap from the disease. Nevertheless, there remains a high risk of fetal damage in offspring of women with the disease, and the possibility that the diets themselves may be harmful cannot be excluded. Search for a preventive treatment for the disease has been greatly aided by advances in molecular genetics. For example, in mice modified liver cells have been implanted, which have not only corrected the phenylalanine defect but have remained healthy for the normal life span of the animal. Overall, however, prevention and treatment have not progressed as quickly as was hoped, and research and development must be pursued vigorously to take account of contemporary perceptions of the disorder.

[Phenylketonuria yesterday and today. Evaluation of the work of systematic neonatal screening]

Phenylketonuria is due in the very great majority of cases to a deficiency in phenylalanine hydroxylase, an enzyme whose cofactor is biopterin. Prenatal screening consists in measuring the concentration of phenylalanine in a sample of dried blood taken after birth (levels are already raised by day 3). Screening, organized by the Association française pour le dépistage et la prévention des handicaps de l'enfant, is very thorough (cover greater than 99%). Treatment involves observance of dietary restriction for at least five years. Results are good. Questions concerning the useful duration of dietary treatment, the level of phenylalanine that should not be exceeded, and the future of girls with PKU remain controversial. When adult, such girls may give birth to retarded children if they do not resume dietary restriction before becoming pregnant. Now that problems of screening, its organization, and the management of diet have been solved, these questions are the new challenge that faces us.

Maternal phenylketonuria collaborative study, obstetric aspects and outcome: the first 6 years

OBJECTIVE

The purpose of this study was to evaluate the efficacy of a phenylalanine-restricted diet in reducing fetal morbidity associated with maternal hyperphenylalaninemia in women of childbearing age with blood phenylalanine levels greater than 240 mumol/L (greater than 4 mg/dl) on an unrestricted diet.

STUDY DESIGN

Two hundred thirteen pregnant women with hyperphenylalaninemia that resulted in 134 live births have been enrolled in the study. Outcome measures were subject to the chi 2 test, Fisher exact test, analysis of variance, t test, or Wilcoxon nonparametric test for analysis.

RESULTS

Optimal fetal outcome appeared to occur when blood phenylalanine levels less than 600 mumol/L (less than 10 mg/dl) were achieved by 8 to 10 weeks' gestation and maintained throughout pregnancy (trimester averages of less than or equal to 360 mumol/L (less than or equal to 6 mg/dl). Initiation of dietary therapy during the third trimester of pregnancy appears to have little beneficial effect on the fetus.

CONCLUSIONS

Preconceptual counseling and early entrance into a prenatal care program is essential in achieving optimal fetal outcome in women with hyperphenylalaninemia.