Reproductive fitness in maternal homocystinuria due to cystathionine beta-synthase deficiency

Inborn errors of metabolism and pregnancy

As the diagnosis and treatment of patients with inborn errors of metabolism has improved dramatically over the years, more people with these conditions are surviving into child-bearing years. Given the changes in metabolism throughout pregnancy, this time presents a unique challenge in their care. Overall metabolic shifts in pregnancy go from anabolism to catabolism driven by endocrinologic changes, along with changes in rates of gluconeogenesis, glucose consumption, amino acid transport, protein consumption, and lipid breakdown, result in a complicated metabolic picture. Additionally, maternal inborn errors of metabolism can affect a fetus, as in phenylketonuria, and fetal inborn errors of metabolism can affect the mother, as in certain fatty acid oxidation disorders. Data on these conditions is often very limited. A summary of the current literature, risks associated with pregnancy in inborn errors of metabolism, and suggestions for management of these conditions will be presented.

Cystathionine Beta-Synthase Deficiency: Three Consecutive Cases Detected in 40 Days by Newborn Screening in Emilia Romagna (Italy) and a Comprehensive Review of the Literature

Cysthiatonine beta-synthase (CBS) deficiency (CBSD) is an autosomal recessive rare disorder caused by variations on CBS that leads to impaired conversion of homocysteine (Hcy) to cystathionine. Marked hyperhomocysteinemia is the hallmark of the disease. The administration of pyridoxine, the natural cofactor of CBS, may reduce total plasma Hcy. Patient phenotype is classified on pyridoxine responsivity in two groups: pyridoxine-responsive and non-responsive patients. Ectopia lentis, bone deformities, developmental delay, and thromboembolism are the classic signs and symptoms of the disease. Early diagnosis and treatment impact patients' natural history. Therapy aims to lower promptly and maintain Hcy concentrations below 100 μmol/L. Depending on the patient's phenotype, the treatment goals could be obtained by the administration of pyridoxine and/or betaine associated with a methionine-restricted diet. CBSD could be diagnosed in the early days of life by expanded newborn screening (ENS), however, the risk of false negative results is not negligible. In Emilia-Romagna (Italy), during the first 10 years of screening experience, only three cases of CBSD identified have been diagnosed, all in the last two years (incidence 1:118,000 live births). We present the cases and a comprehensive review of the literature to emphasize the role of ENS for early diagnosis of CBSD and its potential pitfalls, reiterating the need for a more effective method to screen for CBSD.

The challenges of pregnancy management in pyridoxine nonresponsive homocystinuria: The Irish experience

Many patients with inborn errors of metabolism, due to early diagnosis and improved management, are living longer with less disease burden. Several are now having families of their own. This poses challenges both for the metabolic control of the mother and potential secondary effects on the fetus, as well as the risk of inheriting the inborn error. Classical homocystinuria (HCU, OMIM 236200) is a rare multisystem condition with intellectual, skeletal, ocular, and thromboembolic complications. Ireland has included HCU in the National Newborn Bloodspot Screening Program since 1971. The European network and registry for homocystinurias and methylation defects (E-HOD) guidelines outline the requirements for management and monitoring of this condition and associated complications. Pregnancy alone has many potential complications. When combined with an underlying condition such as HCU, which is prothrombotic and requires a highly medicalized diet, there are significantly increased risks to both mother and baby. Colleagues previously published an Irish case of maternal HCU with successful pregnancy outcome. We add five pregnancies to two women with classical HCU to the literature. We use these to highlight the importance of careful metabolic control and managing the predictable HCU associated risks during pregnancy and the postpartum period. Our cases demonstrate the potential for healthy pregnancies in HCU and that this is best achieved with a motivated clinical team and good patient engagement. Only small numbers of pregnancies in HCU have been reported and we are still learning best practice, but proactive management is essential, as in any inborn error of metabolism.

Current perspective and scope of fetal therapy: part 2

Fetal therapy has been defined as any therapeutic intervention either invasive or noninvasive for correcting or treating any fetal malformation or condition. Invasive fetal therapy have its own set of maternal and fetal complications and invasive approach is not feasible in many of fetal conditions that are candidate for fetal therapy. Many such fetal conditions have been treated successfully by medical or noninvasive management. In medical fetal therapy, mothers are treated with medications which are transferred to fetus through placenta and exert positive effect on the fetus, thus avoiding complications that are seen secondary to invasive fetal therapy. The fetal conditions that have been managed with medical therapy includes fetal and neonatal alloimmune thrombocytopenia, neural tube defect, congenital adrenal hyperplasia, perinatal infections, respiratory distress syndrome, inborn error of metabolism, and congenital cystic adenomatoid malformation. This review will cover the medical or noninvasive aspect of fetal therapy and will highlight the progress made in the management of these fetal conditions.

[Interest of vitamin b6 for treatment of nausea and/or vomiting during pregnancy]

In France there is no official recommendation for the drug management of nausea and vomiting during pregnancy. In the USA, Canada and Australia, vitamin B6 is officially recommended in the treatment of mild to moderate pregnancy sickness and vomiting. Indeed, some studies have shown some effectiveness of oral vitamin B6, most often in combination with doxylamine, in comparison with a placebo. In addition, the harmlessness of oral vitamin B6 during pregnancy has been established for doses up to 40-60mg/day, mainly in combination with doxylamine (40mg/40mg). Thus, in France, as in other countries, vitamin B6 could be integrated into the therapeutic arsenal of mild to moderate nausea and vomiting during pregnancy according to the following dosage schedule: oral intake of 10mg four times a day of a compounded preparation of vitamin B6, alone or in combination with doxylamine.

Nutrition and medical support during pregnancy and lactation in women with inborn errors of intermediary metabolism disorders (IEMDs)

The establishment of expanded newborn screening (NBS) not only results in the early diagnosis and treatment of neonates with inborn errors of intermediary metabolism disorders (IEMDs) but also helps the affected females to reach the reproductive age under medical and dietetic support, as well as to give birth to normal infants. In this review, we aimed to focus on laboratory investigation tests, dietetic management and medical support for most known IEMD pregnant and lactating women, such as those suffering from aminoacidopathies, carbohydrate metabolic diseases and fatty acid (FAO) oxidation disorders.

Genetic variation affecting DNA methylation and the human imprinting disorder, Beckwith-Wiedemann syndrome

Background

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder with a population frequency of approximately 1 in 10,000. The most common epigenetic defect in BWS is a loss of methylation (LOM) at the 11p15.5 imprinting centre, KCNQ1OT1 TSS-DMR, and affects 50% of cases. We hypothesised that genetic factors linked to folate metabolism may play a role in BWS predisposition via effects on methylation maintenance at KCNQ1OT1 TSS-DMR.

Results

Single nucleotide variants (SNVs) in the folate pathway affecting methylenetetrahydrofolate reductase (MTHFR), methionine synthase reductase (MTRR), 5-methyltetrahydrofolate-homocysteine S-methyltransferase (MTR), cystathionine beta-synthase (CBS) and methionine adenosyltransferase (MAT1A) were examined in 55 BWS patients with KCNQ1OT1 TSS-DMR LOM and in 100 unaffected cases. MTHFR rs1801133: C>T was more prevalent in BWS with KCNQ1OT1 TSS-DMR LOM (p < 0.017); however, the relationship was not significant when the Bonferroni correction for multiple testing was applied (significance, p = 0.0036). None of the remaining 13 SNVs were significantly different in the two populations tested. The DNMT1 locus was screened in 53 BWS cases, and three rare missense variants were identified in each of three patients: rs138841970: C>T, rs150331990: A>G and rs757460628: G>A encoding NP_001124295 p.Arg136Cys, p.His1118Arg and p.Arg1223His, respectively. These variants have population frequencies of less than 1 in 1000 and were absent from 100 control cases. Functional characterization using a hemimethylated DNA trapping assay revealed a reduced methyltransferase activity relative to wild-type DNMT1 for each variant ranging from 40 to 70% reduction in activity.

Conclusions

This study is the first to examine folate pathway genetics in BWS and to identify rare DNMT1 missense variants in affected individuals. Our data suggests that reduced DNMT1 activity could affect maintenance of methylation at KCNQ1OT1 TSS-DMR in some cases of BWS, possibly via a maternal effect in the early embryo. Larger cohort studies are warranted to further interrogate the relationship between impaired MTHFR enzymatic activity attributable to MTHFR rs1801133: C>T, dietary folate intake and BWS.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0546-4) contains supplementary material, which is available to authorized users.

Impact of pregnancy on inborn errors of metabolism

Once based mainly in paediatrics, inborn errors of metabolism (IEM), or inherited metabolic disorders (IMD) represent a growing adult medicine specialty. Individually rare these conditions have currently, a collective estimated prevalence of >1:800. Diagnosis has improved through expanded newborn screening programs, identification of potentially affected family members and greater awareness of symptomatic presentations in adolescence and in adulthood. Better survival and reduced mortality from previously lethal and debilitating conditions means greater numbers transition to adulthood. Pregnancy, once contraindicated for many, may represent a challenging but successful outcome. Successful pregnancies are now reported in a wide range of IEM. Significant challenges remain, given the biological stresses of pregnancy, parturition and the puerperium. Known diagnoses allow preventive and pre-emptive management. Unrecognized metabolic disorders especially, remain a preventable cause of maternal and neonatal mortality and morbidity. Increased awareness of these conditions amongst all clinicians is essential to expedite diagnosis and manage appropriately. This review aims to describe normal adaptations to pregnancy and discuss how various types of IEM may be affected. Relevant translational research and clinical experience will be reviewed with practical management aspects cited. Based on current literature, the impact of maternal IEM on mother and/or foetus, as well as how foetal IEM may affect the mother, will be considered. Insights gained from these rare disorders to more common conditions will be explored. Gaps in the literature, unanswered questions and steps to enhance further knowledge and systematically capture experience, such as establishment of an IEM-pregnancy registry, will be summarized.

Potential Misdiagnosis of Hyperhomocysteinemia due to Cystathionine Beta-Synthase Deficiency During Pregnancy

Extreme hyperhomocysteinemia with low cystathionine and cysteine is virtually diagnostic of cystathionine beta-synthase (CBS) deficiency since remethylation defects and hypermethioninemia due to other inborn errors cause elevated serum cystathionine. However, a pregnant CBS deficient patient was found to have elevated cystathionine in addition to elevated total homocysteine and methionine at 23 weeks of gestation and post-delivery cystathionine decreased to the lower level of normal. A second patient with cystathionine values during gestation also showed a rise from the low pre-pregnant value to massive elevation by delivery. Her infant had severe hyperhomocysteinemia in cord blood with a massive elevation of cystathionine, S-adenosylmethionine, and S-adenosylhomocysteine. The infant corrected her homocysteine value by 2 months and is not affected. This data demonstrates that the fetus when exposed to high homocysteine and methionine has increased synthesis of cystathionine which cannot be cleared because the fetus lacks cystathionine gamma-lyase, and thus cystathionine is returned to the mother's circulation. This situation could lead to a misdiagnosis of the cause of hyperhomocysteinemia in a previously undiagnosed pregnant CBS deficient patient. Assays combining homocysteine with cystathionine measurements are commonly available from commercial laboratories in the USA. The recognition of CBS deficiency vs. remethylation disorders is important in order to maximize treatment. The cord blood values revealed a major disturbance in methionine metabolism including a potential for impaired transmethylation reactions in the fetus due to the buildup of S-adenosylhomocysteine. It is possible that monitoring maternal cystathionine during gestation could provide another measure of fetal exposure to homocysteine.

Guidelines for the diagnosis and management of cystathionine beta-synthase deficiency

Cystathionine beta-synthase (CBS) deficiency is a rare inherited disorder in the methionine catabolic pathway, in which the impaired synthesis of cystathionine leads to accumulation of homocysteine. Patients can present to many different specialists and diagnosis is often delayed. Severely affected patients usually present in childhood with ectopia lentis, learning difficulties and skeletal abnormalities. These patients generally require treatment with a low-methionine diet and/or betaine. In contrast, mildly affected patients are likely to present as adults with thromboembolism and to respond to treatment with pyridoxine. In this article, we present recommendations for the diagnosis and management of CBS deficiency, based on a systematic review of the literature. Unfortunately, the quality of the evidence is poor, as it often is for rare diseases. We strongly recommend measuring the plasma total homocysteine concentrations in any patient whose clinical features suggest the diagnosis. Our recommendations may help to standardise testing for pyridoxine responsiveness. Current evidence suggests that patients are unlikely to develop complications if the plasma total homocysteine concentration is maintained below 120 μmol/L. Nevertheless, we recommend keeping the concentration below 100 μmol/L because levels fluctuate and the complications associated with high levels are so serious.

An Overview of Biochemical Genetics

Biochemical genetics focuses on the pathophysiology, diagnosis, and treatment of inherited metabolic disorders. While individually rare, the combined incidence of these diseases makes them a significant source of morbidity and mortality, particularly among infants and young children, and new conditions continue to be identified. Inherited metabolic disorders may present as an acute, life-threatening illness or with more chronic, progressive symptoms. Population-scale newborn screening allows for early detection and treatment for >40 different metabolic disorders. This introductory unit is intended to provide an overview of the different clinical categories of metabolic disorders, including a description of modern diagnostic methods and treatment options.

Medical Problems in Obstetrics: Inherited Metabolic Disease

An increasing number of women with rare inherited disorders of metabolism are becoming pregnant. Although, in general, outcomes for women and their children are good, there are a number of issues that need to be considered. Currently, limited specific guidance on the management of these conditions in pregnancy is available. Prepregnancy counselling with information on inheritance, options for reproduction, teratogenicity risk, potential impact on maternal health and long-term health of children should be offered. With appropriate specialist management, the teratogenic risk of conditions such as maternal phenylketonuria (PKU) can be eliminated, and the risk of metabolic decompensation in disorders of energy metabolism or intoxication significantly reduced. Multidisciplinary management, and close liaison between obstetricians and other specialists, is required for those women in whom there is cardiac, renal, respiratory, joint or other organ involvement.

Pregnancy in women with inherited metabolic disease

An increasing number of women with rare inherited disorders of metabolism are becoming pregnant. Whilst, in general, outcomes for women and their children are good, there are issues that need to be considered. Due to the rarity of many conditions, there is limited specific guidance available on best management. Prepregnancy counselling with information on inheritance, options for reproduction, teratogenicity risk, potential impact on maternal health and long-term health of children should be offered. With appropriate specialist management, the teratogenic risk of conditions such as maternal phenylketonuria (PKU) can be eliminated, and the risk of metabolic decompensation in other disorders of intoxication or energy metabolism significantly reduced. Newer therapies, such as enzyme replacement therapy, appear to be safe in pregnancy, but specific advice should be sought. Multidisciplinary management, and close liaison between obstetricians and other specialists is required for women in whom there is cardiac, renal, respiratory, joint or other organ involvement.

A series of pregnancies in women with inherited metabolic disease

In this case series we report 12 pregnancies, in women treated at four centres, illustrating some of the issues that may be encountered during pregnancy by women with inherited metabolic disease. We discuss how specific pregnancy, labour and delivery issues for mothers with methylmalonic acidemia, homocystinuria, propionic acidemia, glutaric acidemia type 1, ornithine transcarbamylase (OTC) deficiency and 3-hydroxy-3-methylglutaric(HMG)-CoA lyase deficiency were managed and the outcome for the mother and child in each case. Eight of the 12 pregnancies resulted in the successful delivery of a liveborn infant. Several women experienced decompensation of their condition during pregnancy or the post-partum period. There was one maternal death in a women with 3-hydroxy-3-methylglutaric(HMG)-CoA lyase deficiency. Pre-pregnancy counselling and co-management of high risk medical patients by obstetricians and specialist physicians with an understanding of the relationship between pregnancy and inherited metabolic disease is essential.

An overview of biochemical genetics

Biochemical genetics focuses on the pathophysiology, diagnosis, and treatment of inherited metabolic disorders. While individually rare, the combined incidence of these diseases is likely greater than 1:3000 live births. These conditions may present in the neonatal period as an acute, life-threatening illness, or may manifest later in childhood with symptoms of progressive neurodegeneration, skeletal abnormalities, and/or dysmorphia. The purpose of this introductory unit is to provide an overview of the different clinical categories of metabolic disorders, modern diagnostic methods, and treatment options.

Maternal homocystinuria and Moebius syndrome? Vascular aetiology

A case of Moebius syndrome is reported in an infant of a mother known to have pyridoxine-unresponsive homocystinuria. The authors suggest that Moebius syndrome could result from early vascular insufficiency or disruption occurring early in development related to maternal homocystinuria. Moebius syndrome consists of congenital complete or partial facial nerve palsy with or without paralysis of other cranial nerves and often in association with other malformations of the limbs and orofacial structures, but usually without gross structural brain abnormalities.

Hypermethioninemias of genetic and non-genetic origin: A review

This review covers briefly the major conditions, genetic and non-genetic, sometimes leading to abnormally elevated methionine, with emphasis on recent developments. A major aim is to assist in the differential diagnosis of hypermethioninemia. The genetic conditions are: (1) Homocystinuria due to cystathionine β-synthase (CBS) deficiency. At least 150 different mutations in the CBS gene have been identified since this deficiency was established in 1964. Hypermethioninemia is due chiefly to remethylation of the accumulated homocysteine. (2) Deficient activity of methionine adenosyltransferases I and III (MAT I/III), the isoenzymes the catalytic subunit of which are encoded by MAT1A. Methionine accumulates because its conversion to S-adenosylmethionine (AdoMet) is impaired. (3) Glycine N-methyltrasferase (GNMT) deficiency. Disruption of a quantitatively major pathway for AdoMet disposal leads to AdoMet accumulation with secondary down-regulation of methionine flux into AdoMet. (4) S-adenosylhomocysteine (AdoHcy) hydrolase (AHCY) deficiency. Not being catabolized normally, AdoHcy accumulates and inhibits many AdoMet-dependent methyltransferases, producing accumulation of AdoMet and, thereby, hypermethioninemia. (5) Citrin deficiency, found chiefly in Asian countries. Lack of this mitochondrial aspartate-glutamate transporter may produce (usually transient) hypermethioninemia, the immediate cause of which remains uncertain. (6) Fumarylacetoacetate hydrolase (FAH) deficiency (tyrosinemia type I) may lead to hypermethioninemia secondary either to liver damage and/or to accumulation of fumarylacetoacetate, an inhibitor of the high K(m) MAT. Additional possible genetic causes of hypermethioninemia accompanied by elevations of plasma AdoMet include mitochondrial disorders (the specificity and frequency of which remain to be elucidated). Non-genetic conditions include: (a) Liver disease, which may cause hypermethioninemia, mild, or severe. (b) Low-birth-weight and/or prematurity which may cause transient hypermethioninemia. (c) Ingestion of relatively large amounts of methionine which, even in full-term, normal-birth-weight babies may cause hypermethioninemia.

An overview of biochemical genetics

Biochemical genetics is focused on the pathophysiology, diagnosis, and treatment of inborn errors of metabolism, which result in potentially toxic accumulation of substrate or secondary metabolites, and/or inhibition of reaction products. Early-onset metabolic disorders often present during infancy as acute, life-threatening illnesses; other forms of inborn errors appear later in childhood and are often characterized by progressive neurodegeneration. This unit provides an overview of modern biochemical genetic diagnostic methods used to evaluate a patient's metabolic status via measurement of reaction products or a specific enzyme activity. One such technique, tandem mass spectrometry (MS/MS), has revolutionized population-scale newborn screening for metabolic disorders by providing rapid, accurate, multianalyte quantification on small samples. The combination of expanded newborn screening and novel therapeutic approaches, such as enzyme-replacement therapy, offers significant improvement in the management of metabolic disorders.

Impact of folate and homocysteine metabolism on human reproductive health

Folates belong to the vitamin B group and are involved in a large number of biochemical processes, particularly in the metabolism of homocysteine. Dietary or genetically determined folate deficiency leads to mild hyperhomocysteinemia, which has been associated with various pathologies. Molecular mechanisms of homocysteine-induced cellular dysfunction include increased inflammatory cytokine expression, altered nitric oxide bioavailability, induction of oxidative stress, activation of apoptosis and defective methylation. Whereas the involvement of folate metabolism and homocysteine in ageing-related diseases, in several developmental abnormalities and in pregnancy complications has given rise to a large amount of scientific work, the role of these biochemical factors in the earlier stages of mammalian reproduction and the possible preventive effects of folate supplementation on fertility have, until recently, been much less investigated. In the present article, the possible roles of folates and homocysteine in male and female subfertility and related diseases are systematically reviewed, with regard to the epidemiological, pathological, pharmacological and experimental data of the literature from the last 25 years.

Pregnancy issues in inherited metabolic disorders

Increasing numbers of individuals with inherited metabolic disorders are surviving into adulthood and considering their reproductive options. This paper discusses a practical approach to supporting such individuals, focusing on issues concerning fertility, the impact of pregnancy on metabolism and the metabolic disorder itself on the pregnancy, as well as highlighting the need to pay special attention during the postpartum period. Apart from pregnancies in women with phenylketonuria, there is a dearth of data in this area and a great need for collection of information within registries to aid our understanding of potential problems and counselling of women and their partners.

Maternal histidinaemia: pregnancies and offspring outcomes

Untreated pregnancies and their outcomes were studied in 10 women with histidinaemia and their 26 pregnancies. The mean maternal assigned histidine level was 727+/-186 micromol/L (range 484-1,053). Six women had classic histidinaemia (assigned level >700 micromol/L) and the remaining four had mild (atypical) histidinaemia. The pregnancies were uneventful, with only one spontaneous loss and 25 live births. Birth measurements were normal and no congenital anomalies were observed. Growth and development were normal in all offspring. IQ among the 23 offspring tested was 103+/-12 (range 79-122). Four offspring required special education for brief periods and one for several years, but this frequency, as well as that of 12% for attention deficit hyperactive disorder, was not significantly different from expected in the general population. It would appear that maternal histidinaemia, unlike maternal phenylketonuria, can be added to the list of maternal inborn errors of metabolism that are nonteratogenic.

Two successful pregnancies in pyridoxine-nonresponsive homocystinuria

Two successful pregnancies are reported in a pyridoxine-nonresponsive woman who was also homozygous for the MTHFR 677C>T polymorphism. Two healthy children were delivered, although there had also been an early miscarriage of an apparently normal fetus in another pregnancy. Management of the patient's homocystine and methionine levels was maintained throughout pregnancy and, in view of the increased thromboembolic risk, anticoagulation therapy was also included in management.