Dihydrofolate reductase deficiency causing megaloblastic anemia in two families

Dihydrofolate reductase deficiency due to a homozygous DHFR mutation causes megaloblastic anemia and cerebral folate deficiency leading to severe neurologic disease

The importance of intracellular folate metabolism is illustrated by the severity of symptoms and complications caused by inborn disorders of folate metabolism or by folate deficiency. We examined three children of healthy, distantly related parents presenting with megaloblastic anemia and cerebral folate deficiency causing neurologic disease with atypical childhood absence epilepsy. Genome-wide homozygosity mapping revealed a candidate region on chromosome 5 including the dihydrofolate reductase (DHFR) locus. DHFR sequencing revealed a homozygous DHFR mutation, c.458A>T (p.Asp153Val), in all siblings. The patients' folate profile in red blood cells (RBC), plasma, and cerebrospinal fluid (CSF), analyzed by liquid chromatography tandem mass spectrometry, was compatible with DHFR deficiency. DHFR activity and fluorescein-labeled methotrexate (FMTX) binding were severely reduced in EBV-immortalized lymphoblastoid cells of all patients. Heterozygous cells displayed intermediate DHFR activity and FMTX binding. RT-PCR of DHFR mRNA revealed no differences between wild-type and DHFR mutation-carrying cells, whereas protein expression was reduced in cells with the DHFR mutation. Treatment with folinic acid resulted in the resolution of hematological abnormalities, normalization of CSF folate levels, and improvement of neurological symptoms. In conclusion, the homozygous DHFR mutation p.Asp153Val causes DHFR deficiency and leads to a complex hematological and neurological disease that can be successfully treated with folinic acid. DHFR is necessary for maintaining sufficient CSF and RBC folate levels, even in the presence of adequate nutritional folate supply and normal plasma folate.

Identification and characterization of an inborn error of metabolism caused by dihydrofolate reductase deficiency

Dihydrofolate reductase (DHFR) is a critical enzyme in folate metabolism and an important target of antineoplastic, antimicrobial, and antiinflammatory drugs. We describe three individuals from two families with a recessive inborn error of metabolism, characterized by megaloblastic anemia and/or pancytopenia, severe cerebral folate deficiency, and cerebral tetrahydrobiopterin deficiency due to a germline missense mutation in DHFR, resulting in profound enzyme deficiency. We show that cerebral folate levels, anemia, and pancytopenia of DHFR deficiency can be corrected by treatment with folinic acid. The characterization of this disorder provides evidence for the link between DHFR and metabolism of cerebral tetrahydrobiopterin, which is required for the formation of dopamine, serotonin, and norepinephrine and for the hydroxylation of aromatic amino acids. Moreover, this relationship provides insight into the role of folates in neurological conditions, including depression, Alzheimer disease, and Parkinson disease.

Epigenetics: prenatal exposure to genistein leaves a permanent signature on the hematopoietic lineage

Recent studies demonstrate that maternal diet during pregnancy results in long-lasting effects on the progeny. Supplementation of maternal diet with genistein, a phytoestrogen ubiquitous in the daily diet, altered coat color of agouti mice due to epigenetic changes. We studied hematopoiesis of mice prenatally exposed to genistein (270 mg/kg feed) compared with that of mice prenatally exposed to phytoestrogen-poor feed and observed a significant increase in granulopoiesis, erythropoiesis, and mild macrocytosis at the adult age of 12 wk. Genistein exposure was associated with hypermethylation of certain repetitive elements, which coincided with a significant down-regulation of estrogen-responsive genes and genes involved in hematopoiesis in bone marrow cells of genistein-exposed mice, as assessed by microarray technology. Although genistein exposure did not affect global methylation in fetal liver of fetuses at embryonic day 14.5, it accelerated the switch from primitive to definitive erythroid lineage. Taken together, our data demonstrate that prenatal exposure to genistein affects fetal erythropoiesis and exerts lifelong alterations in gene expression and DNA methylation of hematopoietic cells.

Nuclear translocation of dihydrofolate reductase is not a pre-requisite for DNA damage induced apoptosis

Dihydrofolate reductase (DHFR) is a key enzyme for the synthesis of thymidylate, and therefore, of DNA. By applying subcellular proteomic analysis, we identified that the DHFR protein was translocated from cytoplasm into the nucleus when apoptosis was induced by NSC606985, a camptothecin analogue. The nuclear translocation of DHFR protein during apoptosis was independent of the cellular context, but it was more sensitive in cell death induction by DNA damaging agents such as doxorubicin, etoposide and ultraviolent radiation than endoplasmic reticulum stressors (brefeldin-A and tunicamycin) and anti-microtubule agents (paclitaxel and nocodozole). The addition of methotrexate almost completely blocked the nuclear translocation of DHFR protein. Further investigations showed that the nuclear translocation of DHFR was not a pre-requisite for DNA damage induced apoptosis. Therefore, its potential biological significance remains to be further explored.

Molecular genetic analysis of the human dihydrofolate reductase gene: relation with plasma total homocysteine, serum and red blood cell folate levels

Disturbances in folate metabolism may increase the risk of certain malignancies, congenital defects and cardiovascular diseases. The gene dihydrofolate reductase (DHFR) is primarily involved in the reduction of dihydrofolate, generated during thymidylate synthesis, to tetrahydrofolate in order to maintain adequate amounts of folate for DNA synthesis and homocysteine remethylation. In order to reveal possible variation that may affect plasma total homocysteine (tHcy), serum folate and red blood cell (RBC) folate levels, we sequenced the DHFR coding region as well as the intron-exon boundaries and DHFR flanking regions from 20 Caucasian individuals. We identified a 9-bp repeat in the 5'-upstream region that partially overlapped with the 5'-untranslated region, and several single-nucleotide polymorphisms, all in non-coding regions. We screened subjects for the 9-bp repeat (n=417), as well as the recently reported 19-bp deletion in intron 1 (n=330), and assessed their associations with plasma tHcy, serum and RBC folate levels. The 19-bp del/del genotype was associated with a lower plasma tHcy (-14.4% [95% confidence interval: -23.5 to -4.5], P=0.006) compared with the wild-type genotype. This may suggest that intracellular folate levels are affected.

Cloning and mapping of a cDNA for methionine synthase reductase, a flavoprotein defective in patients with homocystinuria

Methionine synthase catalyzes the remethylation of homocysteine to methionine via a reaction in which methylcobalamin serves as an intermediate methyl carrier. Over time, the cob(I)alamin cofactor of methionine synthase becomes oxidized to cob(II)alamin rendering the enzyme inactive. Regeneration of functional enzyme requires reductive methylation via a reaction in which S-adenosylmethionine is utilized as a methyl donor. Patients of the cblE complementation group of disorders of folate/cobalamin metabolism who are defective in reductive activation of methionine synthase exhibit megaloblastic anemia, developmental delay, hyperhomocysteinemia, and hypomethioninemia. Using consensus sequences to predicted binding sites for FMN, FAD, and NADPH, we have cloned a cDNA corresponding to the "methionine synthase reductase" reducing system required for maintenance of the methionine synthase in a functional state. The gene MTRR has been localized to chromosome 5p15.2-15.3. A predominant mRNA of 3.6 kb is detected by Northern blot analysis. The deduced protein is a novel member of the FNR family of electron transferases, containing 698 amino acids with a predicted molecular mass of 77,700. It shares 38% identity with human cytochrome P450 reductase and 43% with the C. elegans putative methionine synthase reductase. The authenticity of the cDNA sequence was confirmed by identification of mutations in cblE patients, including a 4-bp frameshift in two affected siblings and a 3-bp deletion in a third patient. The cloning of the cDNA will permit the diagnostic characterization of cblE patients and investigation of the potential role of polymorphisms of this enzyme as a risk factor in hyperhomocysteinemia-linked vascular disease.

Congenital errors of folate metabolism

Congenital errors of folate metabolism can be related either to defective transport of folate through various cells or to defective intracellular utilization of folate due to some enzyme deficiencies. Defective transport of folate across the intestine and the blood-brain barrier was reported in the condition 'Congenital Malabsorption of Folate'. This disease is characterized by a severe megaloblastic anaemia of early appearance associated with mental retardation. Anaemia is folate-responsive, but neurological symptoms are only poorly improved because of the inability to maintain adequate levels of folate in the CSF. A familial defect of cellular uptake was described in a family with a high frequency of aplastic anaemia or leukaemia. An isolated defect in folate transport into CSF was identified in a patient suffering from a cerebellar syndrome and pyramidal tract dysfunction. Among enzyme deficiencies, some are well documented, others still putative. Methylenetetrahydrofolate reductase deficiency is the most common. The main clinical findings are neurological signs (mental retardation, seizures, rarely schizophrenic syndromes) or vascular disease, without any haematological abnormality. Low levels of folate in serum, red blood cells and CSF associated with homocystinuria are constant. Methionine synthase deficiency is characterized by a megaloblastic anaemia occurring early in life that is more or less folate-responsive and associated with mental retardation. Glutamate formiminotransferase-cyclodeaminase deficiency is responsible for massive excretion of formiminoglutamic acid but megaloblastic anaemia is not constant. The clinical findings are a more or less severe mental or physical retardation. Dihydrofolate reductase deficiency was reported in three children presenting with a megaloblastic anaemia a few days or weeks after birth, which responded to folinic acid. The possible relationship between congenital disorders such as neural tube defects or dihydropteridine reductase deficiency and disturbances of folate metabolism are discussed. Neurological symptoms present in most of these congenital disorders highlight the role of folate in the central nervous system.

Folate metabolism and neural tube defects: a review

The importance of folate in normal fetal development and wellbeing has been recognized only during the past three decades and knowledge concerned is still far from complete. In man, folate acts as a substrate in the transfer of one-carbon moieties and thereby, plays an essential role in the synthesis of several amino acids such as methionine and nucleic acids. Consequently, folate requirements are related to the amount of tissue growth. Epidemiological, clinical and teratological research showed that this B-vitamin is particularly involved in the prevention and pathogenesis of neural tube defects. Therefore, in this review the metabolism of folate has been outlined. Furthermore, the characteristics of the various genically determined folate 'deficiencies' as well as a possible biochemical explanation of the relationship between folate and neural tube defects are being discussed. Finally, the new recommendations launched in November 1993 by the Dutch Health Council as well as the Food and Nutrition Council with regard to folate supplementation in the prevention of neural tube defects are presented.

The neurologic aspects of transcobalamin II deficiency

Thirty-four symptomatic cases of inherited transcobalamin II (TCII) deficiency were analysed in order to determine the frequency and nature of neurologic manifestations. In no instance was there definite evidence of a neurologic disorder at the time of presentation as a young infant. One child of 2 1/2 years transiently lost deep tendon reflexes at a time of suboptimal treatment. A syndrome of mental retardation and other neurologic manifestations was observed in three cases, all with the following in common: (1) an extended duration of illness of 2-17 years; (2) inadequate or not treatment with Cbl; (3) treatment with folic of folinic acid. TCII deficiency rarely if ever presents with neurologic manifestations. However, neurologic disorders can be produced subsequently by improper treatment.

Congenital dyschromia with erythrocyte, platelet, and tryptophan metabolism abnormalities

The case of a female child with a unique generalized congenital dyschromia is reported. She had hypopimented skin, with hypomelanosis and hypomelanocytosis, and many pigmented macules, which consisted of epidermal and dermal hypermelanosis without hypermelanocytosis. Biochemical investigations revealed normal catecholamine metabolism but abnormal tryptophan metabolism, including a decrease in blood serotonin and melatonin. A slight platelet storage pool disease was demonstrated, and a recurrent megaloblastic folate-related anemia occurred. The possible relationship between the pigmentary disease and the biochemical abnormalities is discussed. We suggest that this case represents a previously undescribed association of dyschromia, erythrocyte, platelet, and tryptophan metabolism abnormalities.

Deoxyuridine suppression: biochemical basis and diagnostic applications

The deoxyuridine (dU) suppression test evolved out of investigations into the biochemical basis of the megaloblastic changes seen in vitamin B12 and folate deficiency. Although the abnormality in dU suppression which occurs in vitamin B12- or folate-deficient states is assumed to reflect impaired methylation of deoxyuridylate, there is still no direct demonstration that this is so. Furthermore, there is evidence that reactions other than the methylation of deoxyuridylate are involved in the phenomenon of dU suppression. Nevertheless, in clinical practice abnormal dU suppression serves as a sensitive index of the presence of megaloblastosis due to vitamin B12 or folate deficiency. dU suppression is also abnormal in a number of conditions other than vitamin B12 or folate deficiency, but its overall specificity in detecting tissue dysfunction due to these two deficiency states is considerably higher than that of the serum vitamin B12 or red cell folate levels. Consequently, the test enables us simply and rapidly to define those patients in whom macrocytosis is unrelated to a deficiency of vitamin B12 or folate. For these reasons, the dU suppression test has been adopted by several laboratories across the world for investigating patients with (a) possible vitamin B12 or folate deficiency, (b) macrocytosis, and (c) megaloblastic erythropoiesis. Since the dU suppression test is abnormal in transcobalamin II deficiency and in some congenital disorders of vitamin B12 and folate metabolism, it is very useful in the investigation of obscure anaemias in infancy and childhood. In addition, it has contributed to our understanding of the mechanisms underlying the myelotoxicity of certain drugs, and particularly of nitrous oxide.

Megaloblastic anemia and immune abnormalities in a patient with methionine synthase deficiency

We report a case of methionine synthase deficiency associated with cellular immune deficiency discovered in a 14-year-old boy. Principal findings were: developmental delay, recurrent upper and lower respiratory tract infections, megaloblastic anemia, discovered at 3 months of age, unresponsive to cyanocobalamin and poorly responsive to folinic acid. Biochemical studies showed: an abnormal deoxyuridine suppression test despite normal serum folate, cobalamin and transcobalamin levels; a normal intracellular uptake of these two coenzymes; and an absolute requirement of methionine for fibroblast growth, suggestive of defective methionine synthesis. An absence of methionine synthase activity in the patient's bone marrow and a profound depression of this activity in lymphocytes and liver were found. Hypergammaglobulinemia with variable lymphopenia, depressed lymphocyte transformation after lectin or recall-antigen stimulation, defective delayed-type hypersensitivity and decreased natural killer activity were noted as well. The patient died at the age of 14.

The deoxyuridine suppression test

The deoxyuridine suppression (dU) test, first described in 1964, has gained an important place both in the diagnosis of megaloblastic anemias and in the study of vitamin B12 folate interrelationships in the pathogenesis of megaloblastic anemia. The test measures the integrity of the de novo synthetic pathway of DNA synthesis, in which vitamin B12 and folate play an essential role. The exact mechanism of the test is still largely unknown. However, it is probably the most sensitive and specific functional test for the establishment of vitamin B12 and/or folate deficiency. As such, it is an important diagnostic tool in the investigation of patients suspected of suffering from deficiency of either or both of these vitamins. The test may also have applications towards the study of other factors required for the de novo synthesis of DNA.

Neurological involvement in hereditary transcobalamin II deficiency

A case of hereditary transcobalamin II deficiency with neurological involvement is described. The patient presented in early infancy with megaloblastic anaemia and was treated with folinic acid from 6 weeks of age. The diagnosis of transcobalamin II deficiency was not made until he was 2 years old when he showed severely retarded intellectual development, ataxia and pyramidal deficit in the limbs. Following treatment with hydroxocobalamin, his condition has slowly improved but he has remained with a severe neurological deficit. The consequences of vitamin B12 deficiency on neurological development in infancy are discussed.

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH): an overview

We have reviewed 14 cases of water intoxication in psychiatric patients. In these cases the possibility of the syndrome of inappropriate antidiuretic hormone secretion (SIADH) was suspected or diagnosed. The SIADH should be suspected in psychotic patients who drink water excessively, develop seizures, disorientation and deterioration of mental status.