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

BACKGROUND AND AIMS: Phenylketonuria (PKU)-affected women may become pregnant, and dietary phenylalanine (Phe) intake must be adjusted according to Phe tolerance. We report our experience with maternal PKU in relation to genotype PKU heterogeneity. METHODS AND RESULTS: A total of 10 pregnancies in 7 PKU women (7 different genotypes) were followed up as part of personalized care. Phe tolerance during preconception and pregnancy was assessed by strict dietary control and weekly Phe measurement (blood spots) in relation to genotype. Most women had stopped PKU diet during childhood or adolescence and six pregnancies were unplanned; a phenylalanine-restricted diet was reinstituted soon after conception. Women were classified according to their Phe levels at birth screening and genotype. Phe tolerance increased systematically in the course of pregnancy in all cases, but the increase was different in subjects with classic PKU (cPKU) when compared with cases with mild hyperphenylalaninemia (mHPA), both on average (+297 mg/day in cPKU vs. 597 in mHPA; P = 0.017) and as percentage (+107% in cPKU vs. +17% in mHPA). Notably, Phe tolerance also varied in the same women in the course of different pregnancies, when body weight gain was also different. Two newborns from the same cPKU mother (unplanned pregnancies on free diet) were affected by congenital alterations. CONCLUSIONS: Several factors influence metabolic phenotype in maternal PKU, to an unpredictable extent even in the same woman. The number of maternal PKU cases is growing in dedicated Nutrition Units, and the burden associated with careful management of this condition for the health care system should be adequately considered.

Management of Women With Phenylalanine Hydroxylase Deficiency (Phenylketonuria): ACOG Committee Opinion Summary, Number 802.

Phenylalanine hydroxylase (PAH) deficiency is an autosomal recessive disorder of phenylalanine metabolism that is characterized by insufficient activity of PAH, a hepatic enzyme. Throughout this document, PAH deficiency is used instead of the older nomenclature of phenylketonuria, in order to reflect the spectrum of PAH deficiency and in accordance with the terminology established by the American College of Medical Genetics and Genomics. Aspects of PAH deficiency management that are particularly relevant to obstetrician-gynecologists or other obstetric care providers include the prevention of embryopathy associated with maternal hyperphenylalaninemia and PAH deficiency and the risk of genetic transmission of PAH deficiency. Family planning and prepregnancy counseling are recommended for all reproductive-aged women with PAH deficiency. The fetal brain and heart are particularly vulnerable to high maternal concentrations of phenylalanine. The crucial role played by maternal dietary restriction before and during pregnancy should be stressed in counseling patients with PAH deficiency; the goal should be to normalize blood phenylalanine levels (less than 6 mg/dL) for at least 3 months before becoming pregnant and to maintain at 2-6 mg/dL during pregnancy, in order to optimize developmental outcomes for the fetus. Although phenylalanine levels are increased in the breast milk of patients with PAH deficiency, breastfed infants who do not have PAH deficiency have normal enzyme levels and no dietary restriction. Breastfeeding is safe for infants born to women who have PAH deficiency provided the infants do not have PAH deficiency. Coordinated medical and nutritional care, as well as follow-up with the patient's metabolic geneticist or specialist, are important in the postpartum period. Because newborns with PAH deficiency appear normal at birth and early detection can improve developmental outcomes for children, newborn screening for PAH deficiency is mandated in all states. This Committee Opinion has been revised to include updates on advances in the understanding and management of women with PAH deficiency and recommendations on prepregnancy counseling, serial fetal growth assessments, and fetal echocardiography.

Management of Women With Phenylalanine Hydroxylase Deficiency (Phenylketonuria): ACOG Committee Opinion, Number 802.

Phenylalanine hydroxylase (PAH) deficiency is an autosomal recessive disorder of phenylalanine metabolism that is characterized by insufficient activity of PAH, a hepatic enzyme. Throughout this document, PAH deficiency is used instead of the older nomenclature of phenylketonuria, in order to reflect the spectrum of PAH deficiency and in accordance with the terminology established by the American College of Medical Genetics and Genomics. Aspects of PAH deficiency management that are particularly relevant to obstetrician-gynecologists or other obstetric care providers include the prevention of embryopathy associated with maternal hyperphenylalaninemia and PAH deficiency and the risk of genetic transmission of PAH deficiency. Family planning and prepregnancy counseling are recommended for all reproductive-aged women with PAH deficiency. The fetal brain and heart are particularly vulnerable to high maternal concentrations of phenylalanine. The crucial role played by maternal dietary restriction before and during pregnancy should be stressed in counseling patients with PAH deficiency; the goal should be to normalize blood phenylalanine levels (less than 6 mg/dL) for at least 3 months before becoming pregnant and to maintain at 2-6 mg/dL during pregnancy, in order to optimize developmental outcomes for the fetus. Although phenylalanine levels are increased in the breast milk of patients with PAH deficiency, breastfed infants who do not have PAH deficiency have normal enzyme levels and no dietary restriction. Breastfeeding is safe for infants born to women who have PAH deficiency provided the infants do not have PAH deficiency. Coordinated medical and nutritional care, as well as follow-up with the patient's metabolic geneticist or specialist, are important in the postpartum period. Because newborns with PAH deficiency appear normal at birth and early detection can improve developmental outcomes for children, newborn screening for PAH deficiency is mandated in all states. This Committee Opinion has been revised to include updates on advances in the understanding and management of women with PAH deficiency and recommendations on prepregnancy counseling, serial fetal growth assessments, and fetal echocardiography.

RNA-Seq analysis in an avian model of maternal phenylketonuria.

Cardiac malformations (CVMs) are a leading cause of infant morbidity and mortality. CVMs are particularly prevalent when the developing fetus is exposed to high levels of phenylalanine in-utero in mothers with Phenylketonuria. Yet, elucidating the underlying molecular mechanism leading to CVMs has proven difficult. In this study we used RNA-Seq to investigate an avian model of MPKU and establish differential gene expression (DEG) characteristics of the early developmental stages HH10, 12, and 14. In total, we identified 633 significantly differentially expressed genes across stages HH10, 12, and 14. As expected, functional annotation of significant DEGs identified associations seen in clinical phenotypes of MPKU including CVMs, congenital heart defects, craniofacial anomalies, central nervous system defects, and growth anomalies. Additionally, there was an overrepresentation of genes involved in cardiac muscle contraction, adrenergic signaling in cardiomyocytes, migration, proliferation, metabolism, and cell survival. Strikingly, we identified significant changes in expression with multiple genes involved in Retinoic Acid (RA) metabolism and downstream targets. Using qRTPCR, we validated these findings and identified a total of 42 genes within the RA pathway that are differentially expressed. Here, we report the first elucidation of the molecular mechanisms of cardiovascular malformations in MPKU conducted at early developmental timepoints. We provide evidence suggesting a link between PHE exposure and the alteration of RA pathway. These results are promising and offer novel findings associated with congenital heart defects in MPKU.

Maternal phenylketonuria syndrome: studies in mice suggest a potential approach to a continuing problem.

BackgroundUntreated phenylketonuria (PKU), one of the most common human genetic disorders, usually results in mental retardation. Although a protein-restricted artificial diet can prevent retardation, dietary compliance in adults is often poor. In pregnant PKU women, noncompliance can result in maternal PKU syndrome, where high phenylalanine (Phe) levels cause severe fetal complications. Enzyme substitution therapy using Phe ammonia lyase (PAL) corrects PKU in BTBR Phe hydroxylase (Pahenu2) mutant mice, suggesting a potential for maternal PKU syndrome treatment in humans.MethodsWe reviewed clinical data to assess maternal PKU syndrome incidence in pregnant PKU women. We treated female PKU mice (on normal diet) with PAL, stabilizing Phe at physiological levels, and mated them to assess pregnancy outcomes.ResultsPatient records show that, unfortunately, the efficacy of diet to prevent maternal PKU syndrome has not significantly improved since the problem was first noted 40 years ago. PAL treatment of pregnant PKU mice shows that offspring of PAL-treated dams survive to adulthood, in contrast to the complete lethality seen in untreated mice, or limited survival seen in mice on a PKU diet.ConclusionPAL treatment reduced maternal PKU syndrome severity in mice and may have potential for human PKU therapy.

Methylome repatterning in a mouse model of Maternal PKU Syndrome.

Maternal PKU Syndrome (MPKU) is an embryopathy resulting from in utero phenylalanine (PHE) toxicity secondary to maternal phenylalanine hydroxylase deficient phenylketonuria (PKU). Clinical phenotypes in MPKU include mental retardation, microcephaly, in utero growth restriction, and congenital heart defects. Numerous in utero toxic exposures alter DNA methylation in the fetus. The PAH(enu2) mouse is a model of classical PKU while offspring born of hyperphenylalaninemic dams model MPKU. We investigated offspring of PAH(enu2) dams to determine if altered patterns of DNA methylation occurred in response to in utero PHE exposure. As neurologic deficit is the most prominent MPKU phenotype, methylome patterns were assessed in brain tissue using methylated DNA immunoprecipitation and paired-end sequencing. Brain tissues were assessed in E18.5-19 fetuses of PHE unrestricted PAH(enu2) dams, PHE restricted PAH(enu2) dams, and heterozygous(wt/enu2) control dams. Extensive methylome repatterning was observed in offspring of hyperphenylalaninemic dams while the offspring of PHE restricted dams displayed attenuated methylome repatterning. Methylation within coding regions was dominated by noncoding RNA genes. Differential methylation of promoters targeted protein coding genes. To assess the impact of methylome repatterning on gene expression, brain tissue in experimental and control animals were queried with microarrays assessing expression of microRNAs and protein coding genes. Altered expression of methylome-modified microRNAs and protein coding genes was extensive in offspring of hyperphenylalaninemic dams while minimal changes were observed in offspring of PHE restricted dams. Several genes displaying significantly reduced expression have roles in neurological function or genetic disease with neurological phenotypes. These data indicate in utero PHE toxicity alters DNA methylation in the brain which has downstream impact upon gene expression. Altered gene expression may contribute to pathophysiology of neurologic presentation in MPKU.

Use of sapropterin dihydrochloride in maternal phenylketonuria. A European experience of eight cases.

Sapropterin dihydrochloride (SD) is the first drug treatment for phenylketonuria (PKU), but due to the lack of data, its use in maternal PKU must be undertaken with caution as noted in the FDA and EMEA labels. We collected data from eight pregnancies in PKU women treated with SD and we analysed the phenotypes of these patients, their tetrahydrobiopterin (BH4) responsiveness, the indications for SD treatment, the efficacy (metabolic control, phenylalanine (Phe) tolerance and offspring outcome) and the safety data. Results showed that in the seven patients known to be responsive to BH4, the use of SD during pregnancy was efficient in terms of metabolic control and Phe tolerance. The indications for giving SD included the failure of the low-Phe diet (n = 3), the fact that some of these women had never experienced the low Phe diet (n = 2), one unexpected pregnancy in a woman currently on SD and one pregnancy where the foetus was known to have PKU. The offspring of these seven pregnancies were all normal babies with normal birth measurements and outcomes. No side effect related to SD was observed in these seven cases. In the eighth case, SD was prescribed as a rescue treatment without previous knowledge of the BH4 responsiveness to a woman who was already 8 weeks pregnant without diet. The birth occurred at 33 weeks of gestational age with Potter syndrome (probably related to the absence of metabolic control during the first trimester) and the baby died in the first hours of life. In conclusion, the data presented here provides the first evidence that treatment with pharmacological doses of SD appears to be efficient and safe in women with PKU during pregnancy. Its use should, however, be restricted to those women previously identified to be clear responders to BH4.

Undiagnosed phenylketonuria in parents of phenylketonuric patients, is it worthwhile to be checked?

In our phenylketonuria (PKU) cohort of 120 patients, we uncovered a couple of cases of undiagnosed mild phenylketonuria (mPKU)/hyperphenylalaninemia (mHPA) in maternal parents of the PKU cohort. This finding prompted us to evaluate the risk of either mild phenylketonuria or mild hyperphenylalaninemia in the parent population whose children were diagnosed with hyperphenylalaninemia (HPA). Taking into account the phenylalanine hydroxylase (PAH) mutation carrier frequency and the PAH mild mutation rate, we estimated that the prevalence of the parental mPKU/mHPA varied widely, from 1/74 in Turkey to 1/708 in Lithuania. The benefits of the parental detection procedure described here are the prevention of further maternal PKU syndrome, the follow-up of the newly detected patients and the accuracy of the genetic counseling provided to these families. This very simple procedure should be incorporated into neonatal PKU management of the hospitals in countries where a routine systematic neonatal screening is operational.

Cardiac teratogenicity in mouse maternal phenylketonuria: defining phenotype parameters and genetic background influences.

Maternal phenylketonuria (MPKU) is a syndrome including cardiovascular malformations (CVMs), microcephaly, intellectual impairment, and small size for gestational age, caused by in-utero exposure to elevated serum phenylalanine (Phe) due to PKU in the mother. It is becoming a public health concern as more women with PKU reach child bearing age. Although a mouse model of PKU, BTBR Pah(enu2), has been available for 20 years, it has not been well utilized for studying MPKU. We used this model to delineate critical parameters in Phe cardiovascular teratogenicity and study the effect of genetic background. Dosing and timing experiments were performed with the BTBR Pah(enu2) mouse. A dose response curve was noted, with CVM rates at maternal serum Phe levels <360 µM (control), 360-600 µM (low), 600-900 µM (mid), and >900 µM (high) of 11.86%, 16.67%, 30.86%, and 46.67% respectively. A variety of CVMs were noted on the BTBR background, including double outlet right ventricle (DORV), aortic arch artery (AAA) abnormalities, and ventricular septal defects (VSDs). Timed exposure experiments identified a teratogenic window from embryonic day 8.5-13.5, with higher rates of conotruncal and valve defects occurring in early exposure time and persistent truncus arteriosus (PTA) and aortic arch branching abnormalities occurring with late exposure. Compared to the BTBR strain, N10+ Pah(enu2) congenics on the C3H/HeJ background had higher rates of CVMs in general and propensity to left ventricular outflow tract (LVOT) malformations, while the C57B/L6 background had similar CVM rates but predominately AAA abnormalities. We have delineated key parameters of Phe cardiovascular teratogenicity, demonstrated the utility of this MPKU model on different mouse strains, and shown how genetic background profoundly affects the phenotype.

Tetralogy of Fallot variant with pulmonary atresia (pseudotruncus arteriosus) in a case of maternal PKU syndrome.

The authors report on a child with a rare variant of the Tetralogy of Fallot with pulmonary atresia also known as Pseudotruncus arteriosus, who was born by a mother affected by classic phenylketonuria (PKU), diet free of phenylalanine until the age of seven years. According to the authors, this is the first example of such rare variant in an offspring of maternal PKU syndrome.

Phenylalanine tolerance in three phenylketonuric women pregnant with fetuses of different genetic PKU status.

Pregnancy management in phenylketonuric women includes continuous dietary control starting before conception, aiming to maintain blood phenylalanine concentrations in a desirable range, irrespective of the fetal genetic PKU status. While the maternal phenylalanine hydroxylase (PAH) genotype will influence metabolic control, an effect of the fetal genetic PKU status on maternal metabolic control during pregnancy has not been described. We monitored three pregnancies of women with classical PKU by dietary protocols of daily phenylalanine intake, phenylalanine blood concentrations, and obstetric care. Patients 1 and 2 carried a heterozygous (not PKU-affected) fetus, while patient 3 was pregnant with a PKU-affected fetus (PAH p.R408W and p.R408W). The expected increase in phenylalanine tolerance during the course of pregnancy was observed in patients 1 and 2 in whom phenylalanine intake could be steadily increased from 400 to 1700 mg/day while phenylalanine blood concentrations remained in the desired range. Gain of body weight was 13.0 and 17.7 kg, respectively. In patient 3, the phenylalanine tolerance did not rise above 600 mg/day, and phenylalanine blood concentrations were above the desired range on several occasions. Caloric intake was therefore encouraged, which led to a weight gain of 20.0 kg. The course of pregnancy was otherwise normal in all three cases, and infants with normal birth weight and head circumference were born. The different phenylalanine tolerance in pregnancies with PKU-affected and non-affected fetuses suggests that PAH genotype and metabolic situation of the fetus influence maternal metabolic control. A phenylalanine tolerance remaining low in the third trimester of pregnancy may indicate fetal PKU.

Factors influencing outcomes in the offspring of mothers with phenylketonuria during pregnancy: the importance of variation in maternal blood phenylalanine.

BACKGROUND: Developmental delay in the offspring of women with phenylketonuria (PKU) can be prevented by maintaining maternal blood phenylalanine (Phe) within a target range (100-250 micromol/L). OBJECTIVE: We aimed to analyze outcomes in the offspring of women with PKU during pregnancy and to identify prognostic factors. DESIGN: Occipitofrontal circumference at birth (OFC-B); developmental scores [developmental quotient (DQ) and intelligence quotient (IQ)]at 1, 4, 8, and 14 y; and the time of starting a Phe-restricted diet (before or after conception) were collected. The influence of maternal Phe concentrations during pregnancy on offspring outcomes also was assessed. RESULTS: The study included 105 children born to 67 mothers with PKU. Mean (+/-SD) OFC-B z scores did not differ between the preconception and postconception diet groups (0.42 +/- 1.24 and -0.96 +/- 1.19, respectively). DQ at 1 y and IQ at 8 y were higher in offspring from the preconception diet group than in offspring from the postconception diet group [DQ: 107 +/- 13.8 and 99.3 +/- 13.3, respectively (P = 0.014); IQ: 110.6 +/- 14.8 and 91.2 +/- 23.9, respectively (P = 0.005)]. Maternal Phe concentrations correlated negatively with DQ and IQ scores, and variations (SD) in all maternal blood Phe correlated negatively with 4-, 8-, and 14-y IQ scores (r = -0.385, -0.433, and -0.712; P = 0.002, 0.008, and 0.031, respectively), even when concentrations were consistently within the target range. CONCLUSIONS: The study suggests that women with PKU should start a Phe-restricted diet before conception. Maintenance of maternal blood Phe within the target range predicts good offspring outcomes, but variations even within that range should be avoided.

Finding the fertile woman with phenylketonuria.

This review highlights two groups of women with phenylketonuria (PKU) who are at risk of producing offspring with maternal phenylketonuria (MPKU) embryopathy: (I) those not yet diagnosed; (II) those lost to follow-up. The world literature is reviewed, including that published from the International MPKU Collaborative Study (MPKUCS) and evidence is presented to support our hypothesis that at least 10% of subjects with untreated "classical PKU" will have relatively normal intellectual function and that a significantly higher percentage of the less severe "variants" (who make up approximately 50% of the total) will have IQ's measured within the normal range. The offspring of the females with these PKU variants, however, are not as fortunate-most suffering profound damage in-utero if the pregnant woman is not treated. However, the offspring of the mildest variant (untreated) "non-PKU mild hyperphenylalaninemia (MHP)" - blood phenylalanine 200-600 micromol/L - appear to be unaffected. This latter variant makes up 10-15% of the total. Many of these women, born before neonatal screening began in the jurisdiction of their birth, are unaware of their disease. Others, whose diet was discontinued in childhood, may not remember why they were on special diets. Our literature review has revealed reports, since 1990, of 60 women with previously undiagnosed PKU, most with relatively normal intellectual function, who produced 119 offspring, virtually all profoundly damaged. It is pointed out that the recent trend, in industrialized countries, of delayed child-bearing may be a factor. Reports are presented from various jurisdictions showing that up to 10% of known women with PKU in the reproductive age group have been lost to follow-up. "Selective Prenatal Screening or Case-Finding" for fertile women with PKU is recommended and a template is presented.

Maternal phenylketonuria syndrome and case management implications.

Well-established dietary protocols have prevented mental retardation for infants born with phenylketonuria (PKU). Dietary protocols for managing females with PKU in their reproductive years exist but are not followed by most of them. Infants who are born to mothers with PKU who are not on dietary treatment usually have serious medical problems, such as mental retardation, heart defects, and other serious congenital anomalies (e.g., orofacial clefting and bladder exstrophy)--a condition known as maternal PKU syndrome. The focus of this article is to review the pathophysiology, associated developmental issues, and existing management protocols used to manage these two separate but highly connected disorders.

Tetrahydrobiopterin and maternal PKU.

A 29-year-old woman with PKU is presented, who was successfully treated with phenylalanine restriction as well as oral BH4 during this pregnancy, with a normal outcome. Her PAH mutation was R408W/F39L. Remarkably, the blood phenylalanine control was easily accomplished during this pregnancy. The lack of nausea and vomiting during the first trimester suggests that the occurrence of CHD in babies born to women with PKU may be reduced with BH4.