Nucleotidase Deficiency Research Articles

A rare mutation (p.F149del) of the NT5C3A gene is associated with pyrimidine 5′-nucleotidase deficiency

Pyrimidine 5′-nucleotidase deficiency is a rare erythrocyte enzymopathy. Here we report two cases of hemolytic anemia in brothers of Polish origin that are associated with a very rare mutation. Heterozygous deletion in the NT5C3A gene (c.444_446delGTT), inherited most likely from their asymptomatic mother, resulted in a single amino acid residue deletion (p.F149del) in cytosolic pyrimidine 5′-nucleotidase. However, only the mutated transcript was present in the reticulocyte transcriptome of both patients. Only residual activity of pyrimidine 5′-nucleotidase in the brothers’ erythrocytes could be observed when compared with the controls, including their asymptomatic father and sister. Western blot showed no sign of the presence of 5′-nucleotidase protein in the erythrocytes of both studied patients. The 2.5-fold reduction of the purine/pyrimidine ratio observed only in the brothers’ erythrocytes confirms the correlation of the results of molecular analysis, including whole-exome sequencing, with the phenotype of the pyrimidine 5′-nucleotidase deficiency. Altogether, our results may substantiate the hypothesis of the heterogeneity of the molecular basis of the defect involving both the mutation presented here and negative regulation of expression of the “normal” allele.

Lead Poisoning Induced Severe Hemolytic Anemia, Basophilic Stippling, Mimicking Erythrocyte Pyrimidine 5'-nucleotidase Deficiency in Beta Thalassemia Minor

Lead Poisoning Induced Severe Hemolytic Anemia, Basophilic Stippling, Mimicking Erythrocyte Pyrimidine 5'-nucleotidase Deficiency in Beta Thalassemia Minor

Lead Poisoning Induced Severe Hemolytic Anemia, Basophilic Stippling, Mimicking Erythrocyte Pyrimidine 5'-nucleotidase Deficiency in Beta Thalassemia Minor

Lead Poisoning Induced Severe Hemolytic Anemia, Basophilic Stippling, Mimicking Erythrocyte Pyrimidine 5'-nucleotidase Deficiency in Beta Thalassemia Minor

Proteomics reveals reduced expression of transketolase in pyrimidine 5'-nucleotidase deficient patients.

To date, it remains a challenge to correctly and timely diagnose red blood cell (RBC) enzymopathies that result in hereditary nonspherocytic hemolytic anemia (HNSHA), the third most common of which is pyrimidine 5'-nucleotidase (P5N) deficiency with just over 100 cases recognized and confirmed worldwide. We have investigated the RBC proteome of a patient with P5N deficiency due to a homozygous frameshift mutation in the NT5C3A gene. Protein expression levels were analyzed against healthy controls and against patients with hemolytic anemia of different origin, to account for the patient's elevated reticulocyte versus RBC ratio. Stringent relative quantification of the patient's protein levels revealed reduced levels of P5N, and unexpectedly, also decreased levels of transketolase, an enzyme involved in the nonoxidative phase of the pentose phosphate pathway, one of the few key pathways active in RBCs. Immunoblotting of whole blood samples from this and other P5N-deficient patients with dissimilar mutations indicated that P5N deficiency was correlated with reduced transketolase levels. Consequently, insight into patient RBC proteomes illustrates potential benefit of coupling quantitative proteomics strategies with routine HNSHA diagnostic procedures. Proteomics facilitates finding novel biomarkers for HNSHA patients, for example, suffering from P5N deficiency, providing new prospects for future diagnosis and therapy.

Ecto-5'-Nucleotidase (CD73) Deficiency in Mycobacterium tuberculosis-Infected Mice Enhances Neutrophil Recruitment.

The immune system needs safeguards that prevent collateral tissue damage mediated by the immune system while enabling an effective response against a pathogen. The purinergic pathway is one such mechanism and finely modulates inflammation by sensing nucleotides in the environment. Extracellular ATP is considered to be a danger signal leading to a proinflammatory response, whereas adenosine is immunosuppressive. CD73, also called ecto-5'-nucleotidase, occupies a strategic position in this pathway, as it is the main enzyme responsible for the generation of adenosine from ATP. Here, we explore the role of CD73 during tuberculosis, a disease characterized by an immune response that is harmful to the host and unable to eradicate Mycobacterium tuberculosis. Using CD73 knockout (KO) mice, we found that CD73 regulates the response to M. tuberculosis infection in vitro and in vivo. Mycobacterium-infected murine macrophages derived from CD73 KO mice secrete more keratinocyte chemoattractant (KC), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) and release less vascular endothelial growth factor (VEGF) upon ATP stimulation than do those derived from wild-type (WT) mice. In vivo, CD73 limits the early influx of neutrophils to the lungs without affecting bacterial growth and dissemination. Collectively, our results support the view that CD73 fine-tunes antimycobacterial immune responses.

The Enzymology of Cytosolic Pyrimidine 5’-Nucleotidases: Functional Analysis and Physiopathological Implications.

In mammals, cellular 5'-nucleotidase (5'-NT) activity (EC 3.1.3.5) encompasses a number of genetically and structurally distinct enzyme forms, either membrane-bound or soluble, mainly cytosolic, that are characterized by broad specificity towards nucleoside 5'-monophosphate substrates differing in base (purine/pyrimidine) and/or sugar (oxy/deoxy-ribose) moieties. In particular, among the cytosolic 5'-NTs active towards pyrimidine nucleotides are cN-III and cdN, ubiquitously distributed in mammalian tissues and treated as a single entity in the early days. cN-III was first linked to a genetic defect , hereditary pyrimidine nucleotidase deficiency, associated to a nonspherocyt ic hemolytic anemia disorder of still unclear mechanism but metabolically characterized by abnormally high levels of pyrimidine compounds and ribonucleoproteins in erythrocytes, as evidenced by occurrence of basophilic stippling on blood smearings. Since the first review on pyrimidine-specific nucleotidases (Amici, A.; Magni, G., Arch. Biochem. Biophys., 2002, 397(2), 184- 190), excellent overviews on the topic appeared in the literature. In the present contribution, the major findings on these two enzymatic proteins, cN-III and cdN, will be described with particular emphasis on the relationships between their structure and function, as well as on their roles in normal and pathological conditions. The catalytic mechanism of both specific hydrolytic and phosphotransferase activities, possessed by both enzymes, will be discussed also in the light of recent solution of both cN-III and cdN three-dimensional structures. This review also focuses on possible therapeutic approaches involving cellular 5'-NTs in detoxifying common antiviral and antineoplastic drugs.

Diagnosis of pyrimidine 5′‐nucleotidase deficiency suspected from a blood film

Diagnosis of pyrimidine 5′‐nucleotidase deficiency suspected from a blood film

Identification of Drosophila and Human 7-Methyl GMP-specific Nucleotidases

Turnover of mRNA releases, in addition to the four regular nucleoside monophosphates, the methylated cap nucleotide in the form of 7-methylguanosine monophosphate (m(7)GMP) or diphosphate (m(7)GDP). The existence of pathways to eliminate the modified nucleotide seems likely, as its incorporation into nucleic acids is undesirable. Here we describe a novel 5' nucleotidase from Drosophila that cleaves m(7)GMP to 7-methylguanosine and inorganic phosphate. The enzyme, encoded by the predicted gene CG3362, also efficiently dephosphorylates CMP, although with lower apparent affinity; UMP and the purine nucleotides are poor substrates. The enzyme is inhibited by elevated concentrations of AMP and also cleaves m(7)GDP to the nucleoside and two inorganic phosphates, albeit less efficiently. CG3362 has equivalent sequence similarity to two human enzymes, cytosolic nucleotidase III (cNIII) and the previously uncharacterized cytosolic nucleotidase III-like (cNIII-like). We show that cNIII-like also displays 5' nucleotidase activity with a high affinity for m(7)GMP. CMP is a slightly better substrate but again with a higher K(m). The activity of cNIII-like is stimulated by phosphate. In contrast to cNIII-like, cNIII and human cytosolic nucleotidase II do not accept m(7)GMP as a substrate. We suggest that the m(7)G-specific nucleotidases protect cells against undesired salvage of m(7)GMP and its incorporation into nucleic acids.

The PRPP Synthetase Spectrum: What Does it Demonstrate About Nucleotide Syndromes?

Defects in X-linked phosphoribosylpyrophosphate synthetase 1 (PRPS1) manifest as follows: (1) PRS-I enzyme “superactivity” (gain-of-function mutations affecting allosteric regions); (2) PRS-I overexpression (which may be linked to miRNA mutation); (3) severe PRS-I deficiency/Arts syndrome (missense mutations producing loss-of-function); (4) moderate PRS-I deficiency/Charcot–Marie–Tooth disease-5 (less severe loss-of-function mutations); and (5) mild PRS-I deficiency/Deafness-2 (mutations producing slight destabilization). Similar to Lesch–Nyhan disease, PRPS1-related disorders arise from phosphoribosyl-pyrophosphate (PRPP)-dependent nucleotide “depletion” of purine nucleotides (e.g., ATP, GTP). S-adenosylmethionine (SAMe) appears to partially alleviate purine depletion via a PRPP-independent path. Synthesis of pyrimidine nucleotides is PRPP dependent, with uridine monophosphate synthase deficiency producing pyrimidine nucleotide depletion. But pyrimidine salvage from uridine does not require PRPP, and this nucleoside is transported freely to pyrimidine-depleted tissues. Regulation of nicotinamide nucleotides is less clear; synthesis from pyridine nucleobases is PRPP dependent. Nucleotide “depletion” contrasts with nucleotide “toxicity,” exemplified by the purine disorders adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiencies or by pyrimidine nucleotidase deficiency. These are characterized by the accumulation of one or more abnormal nucleotides such as succinyl- or deoxy-nucleotides or their metabolites, which interrupt other nucleotide or related pathways or are toxic to specific cell types. Theoretically, purine toxicity disorders would not be ameliorated by SAMe therapy, and this was confirmed for one adenylosuccinate lyase-deficient child. Nucleotide defects may also be seen as an aspect of mitochondrial disease, with SAMe-based mitochondrial therapy perhaps meriting further investigation.

Hepcidin Production in Ineffective Erythropoiesis and Chronic Hemolysis: Insights on the Crosstalk Between Erythropoiesis and Iron Metabolism

Abstract 346 Background and Aims:Ineffective erythropoiesis in thalassemias and congenital dyserythropoietic anemia has been associated with hepcidin deficiency and spontaneous iron overload, potentially mediated by an abnormally high production of GDF-15, a cytokine overexpressed by maturing erythroblasts (Tanno et al. Nat Med 2007;13:1096–101; Tamary et al., Blood 2008; 112:5241–5244). In this study, we focused on analyzing hepcidin levels in different disorders affecting red cell production. Patients and Methods:Twenty patients with transfusion independent β-thalassemia intermedia (TI) were enrolled as a model of hemoglobinopathy with ineffective erythropoiesis, and were compared to 53 patients with sickle cell anemia (SCA), in which erythropoiesis is effective. Seventeen healthy volunteers and 13 patients with other anemic states with chronic hemolysis (hereditary spherocytosis, autoimmune hemolytic anemia, pyrimidine 5’-nucleotidase deficiency) were recruited for comparison. Fourteen patients with megaloblastic anemia due to cobalamin deficiency were studied before, during and after treatment as an alternative model of ineffective erythropoiesis. We have determined hepcidin levels as previously described (Ganz et al. Blood 2008;112:4292–4297), as well as serum ferritin, transferrin saturation (TS) and GDF-15 in all groups. Levels of C reactive protein (CRP) and IL-6, an inducer of hepcidin production, were also determined in controls, SCA and TI. Results and Discussion:IL-6 levels in SCA patients were increased [mean± standard error of mean (1.69±0.22pg/ml, p=0.047)] when compared to TI (1.33±0.21pg/ml) and controls (0.77±0.18pg/ml), and although there was a positive correlation between IL-6 and hepcidin levels (rS=0.25, p=0.039) this did not correspond to an absolute increase in hepcidin in this group. Indeed, circulating hepcidin levels were lower both in TI (56.24±12.14ng/ml) and SCA patients (52.53±10.97ng/ml) than in controls and other hemolytic anemias (80.23±14.3ng/ml and 120.7±12.2ng/ml, respectively, p=0.013), and did not correlate with the elevated levels of GDF-15 found in the 3 groups of patients (p>0.05). Ferritin levels correlated with both hepcidin and GDF-15 levels (rS=0.38, p=0.0005, and rS=0.63, p<0.0001, respectively). CRP correlated only weakly with IL-6 (rS=0.26, p=0.03) and was not significantly different among the groups studied. Ferritin and TS were considerably higher in TI patients than in the remaining groups (p=0.003). Ineffective erythropoiesis in cobalamin deficiency was neither associated with spontaneous ferritin or TS elevation, nor with decreased hepcidin in spite of high GDF-15 levels. Hepcidin levels at the time of diagnosis were higher than those in SCA (p<0.01) and decreased during vitamin B12 supplementation (108.8±23.36ng/ml vs. 59.37±16.23ng/ml, p=0.045). Hepcidin/ferritin ratios were significantly lower in SCA (28.91±3.08) and TI (13.76±3.98) than in controls and cobalamin deficiency (320.1±109.2 and 279.9±60.2, respectively, p<0.0001, graph represents minimum/maximum values and quartiles), better representing relative hepcidin deficiency in hemoglobin disorders than isolated hepcidin levels. Conclusions:Although both ineffective erythropoiesis and chronic hemolysis were associated with high levels of GDF-15 and low hepcidin in hemoglobinopathies as a result of erythroid compartment expansion, a similar pattern was not confirmed in other hemolytic anemias or megaloblastic anemia. In the latter case, ineffective erythropoiesis did not suppress hepcidin, and regulation of hepcidin production during recovery seemed intact and occurred independently from hepcidin-inhibitory GDF-15 production. Despite elevated IL-6 levels in SCA, chronic inflammation appeared insufficient to overcome the influence of the erythropoietic drive to increase overall hepcidin levels in these patients, but might explain why hepcidin/ferritin ratios in SCA are higher than in TI patients, and normal hepcidin/ferritin ratios corresponded to normal iron status in cobalamin deficiency patients. Our data suggest that hepcidin/ferritin ratio may be a more accurate measurement to detect patients prone to systemic iron overload secondary to increased erythropoietic activity, and corroborate the concept that chronic inflammation may protect SCA from overt iron overload to some extent. [Display omitted] Disclosures:Olbina:Intrinsic LifeSciences LLC: Employment, Equity Ownership; Hepcidin C-ELISA: Co-developer. Westerman:Intrinsic LifeSciences LLC: Employment, Equity Ownership, Membership on an entity’s Board of Directors or advisory committees; Hepcidin C-ELISA: Patents & Royalties; Centocor-Ortho R&D, Inc.: Honoraria.

Molecular basis of pyrimidine 5′-nucleotidase deficiency caused by 3 newly identified missense mutations (c.187T>C, c.469G>C and c.740T>C) and a tabulation of known mutations

Hereditary pyrimidine 5′-nucleotidase deficiency is the most frequent enzymopathy of red blood cell nucleotide metabolism that causes hereditary non-spherocytic hemolytic anemia. The disease is usually characterized by mild-to-moderate hemolytic anemia, reticulocytosis and hyperbilirubinemia. To date, diagnosis ultimately depends upon demonstration of a reduced level of pyrimidine 5′-nucleotidase type-I (P5′N-1) activity in red cells and detection of mutations in the P5′N-1 gene. To unravel the causes of the P5′N deficiency and to obtain data for a definitive diagnosis three newly described missense mutations (c.187T>C, c.469G>C and c.740T>C) identified in patients with hemolytic anemia have been characterized at protein level. The mutant enzymes (C63R, G157R and I247T) were obtained as recombinant forms and purified to homogeneity. The enzymes were altered, although to a different extent, in both thermal stability and catalytic efficiency. The catalytic efficiency of all mutants was reduced especially towards UMP (up to more than 200 times), owing to the increased K m values (approximately, 10–25 times higher). The G157R enzyme was severely heat unstable and lost half of its activity after about 23 min of incubation at 37 °C. At higher temperature C63R and I247T mutants as well were less stable than the wild-type enzyme. Therefore, although the mutations targeted different regions of the P5′N-1 structure, they produced similar effects on the molecular properties of the enzyme. Thus, all affected amino acids are functionally and structurally important for preserving the enzyme activity during the red cell life span.

Hereditary pyrimidine 5′‐nucleotidase deficiency: from genetics to clinical manifestations

Hereditary pyrimidine 5'-nucleotidase (P5'N) deficiency is the most frequent abnormality of the red cell nucleotide metabolism causing hereditary non-spherocytic haemolytic anaemia. The disorder is usually characterised by mild-to-moderate haemolytic anaemia associated with the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. The precise mechanisms leading to the destruction of P5'N deficient red cells are still unclear. The pyrimidine 5'-nucleotidase type-I (P5'N-1) gene is localised on 7p15-p14 and the cDNA has been cloned and sequenced; 20 mutations have been identified so far in 30 unrelated families, most of them at the homozygous level. Recently, the comparison of recombinant mutants of human P5'N-1 with the wild-type enzyme has enabled the effects of amino acid replacements on the enzyme molecular properties to be determined and help to correlate genotype to clinical phenotype.

Hereditary erythrocyte pyrimidine 5′-nucleotidase deficiency: A biochemical, genetic and clinical overview

Pyrimidine 5′-nucleotidase (P5′N–1) deficiency is the third most common enzyme abnormality after glucose 6-phosphate dehydrogenase and pyruvate kinase causing hereditary non-spherocytic hemolytic anemia. The disease is transmitted as an autosomal recessive trait. The degree of hemolysis is generally mild-to moderate. The hallmark of this enzyme deficiency is the presence of pronounced basophylic stippling in red blood cell peripheral blood smear together with accumulation of pyrimidine nucleotides within erythrocytes. No correlation has been found between residual activity and degree of hemolysis. The structural human gene for P5′N–1 is now available and fifteen different mutations had been identified so far. More recently, a functional analysis of P5′N–1 mutants had been performed providing a rationale for the pathological effects of the mutations. All mutations investigated affect amino acid residues unambiguously essential for the catalytic efficiency and/or protein stability, suggesting drastic reduction of the enzyme activity in red blood cells of patients affected by the disorder. Nevertheless, some patients exhibit high residual P5′N–1 activity, suggesting that P5′N–1 deficiency is compensate by other nucleotidases and/or alternative pathways in nucleotide metabolism. No specific therapy for P5′N–1 deficiency is now available.

Pyrimidine 5′ Nucleotidase Deficiency: Clinical and Molecular Characterization of Two New Italian Patients.

Hereditary pyrimidine 5′ nucleotidase deficiency (P5′N) is the most frequent abnormality of the red cell nucleotide metabolism causing hereditary non-spherocytic hemolytic anemia. The disorder is characterized by mild-to-moderate hemolytic anemia associated with reticulocytosis and hyperbilirubinemia and the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. P5′N-1 gene is localized on 7p15-p14; eighteen mutations have been so far identified in 27 unrelated families, 6 of them of Italian origin. The aim of this study is to describe the hematological, biochemical and molecular characteristics of two new Italian patients affected by P5′N deficiency. Case1: The propositus was a 37 yrs old woman of Northern Italian origin affected by chronic hemolytic anemia with Hb levels ranging from 8.2 to 10.5 g/dL. At the time of the study Hb was 8.4 g/dL, reticulocytes 300x109/L, unconjugated bilirubin 3.2 mg/dL. Peripheral blood smear examination showed basophilic stippling and purines/pyrimidines ratio (OD260/280) was decreased (1, ref. values 1.4 – 2.98). P5′N activity, measured by capillary electrophoresis, was undetectable. Molecular analysis of P5′N-1 gene showed the presence of a new homozygous deletion of two bp (ag) at the splice junction between intron 7 and exon 8, which probably results in a splicing alteration and in the absence of a functional protein. Case2: The propositus, a 37 yrs old woman of Northern Italian origin carrying the hemoglobin variant HbD Punjab, had an history of chronic hemolytic anemia since childhood; at the age of 14 yrs splenectomy and colecystectomy were performed. The patient needed blood transfusions because of exacerbation of anemia (Hb 4.7g/dL) during parvovirus B19 infection. Iron status parameters were increased requiring desferrioxamine treatment. At the time of the study Hb was 9.3 g/dL, reticulocytes 752x109/L, unconjugated bilirubin 13.3 mg/dL. Serum ferritin was 1980 mg/mL and transferrin saturation 115%. The propositus was found to be homozygous for Gilbert's syndrome and heterozygous for mutation H63D of HFE gene. Basophilic stippling (6%) was observed in peripheral blood smear. Pur/pyr ratio was 0.8 and residual P5′N activity was 40% of normal. Complete sequencing of P5′N-1 gene showed the presence of the frameshift mutation ins GG710-711, already described in Italian and Turkish patients, and the new in-frame aminoacidic deletion of Gln 143.

Molecular basis of Japanese variants of pyrimidine 5'-nucleotidase deficiency.

The type-I isoform of pyrimidine 5'-nucleotidase (P5N-I) has an important role in the catabolism of pyrimidine mononucleotides during erythroid maturation. Two alternatively spliced forms of P5N-I mRNA have been identified, and we found another alternatively spliced form in reticulocytes, which included an additional 87-bp sequence. The sequence is located 6.2-kb downstream of the exon 2 and 2.7-kb upstream of the exon 3 sequence; consequently, the P5N-I gene encodes 11 exons, which span approximately 48 kb. We identified five novel mutations in nine families with P5N-I deficiency: two missense mutations (425C, 721C), one splice mutation (339C), one 1-bp insertion (251-insA-252) and one 9-bp deletion (del 192-200). All patients were homozygous for each mutation. The mutant P5N-I with 721C (G241R) had lower affinity for cytidine monophosphate, suggesting that Gly241 is important for substrate binding. Haplotype analysis showed that 721C, which had been identified in five unrelated families, was a founder mutation. The mutant P5N was then expressed in Cos-7. The degradation of P5N with 425C (L142P) was significantly faster than a wild-type control, and proteasome inhibitors restored the stability of L142P. These data suggest that L142P increases susceptibility to the degradation by the ubiquitin-proteasome pathway.

Adenosine

Adenosine has been recognized as a potentially important signaling molecule in the heart for nearly a half century. The original adenosine hypothesis proposed that production of adenosine by cardiac myocytes reflects the metabolic state of the myocardium and serves to regulate vasomotor tone in the coronary resistance vessels, thereby coupling blood flow to the energetic needs of the heart.1 There are two major pathways for adenosine production in the cardiac myocyte. The transmethylation pathway involves the hydrolysis of S -adenosylhomocysteine (SAH) by SAH hydrolase to l-homocysteine and adenosine. A second pathway, the hydrolysis of AMP by 5′-nucleotidase, predominates during ischemic or hypoxic conditions.2 According to the adenosine hypothesis, when the energy requirements of the heart increase, the increased rate of ATP hydrolysis would cause cytosolic free ADP levels to rise. In this situation, the myokinase reaction can utilize two molecules of ADP to produce one molecule each of ATP and AMP, the later being the substrate for 5′-nucleotidase to produce adenosine, which can enter the interstitial space to cause coronary vasodilation. Although this hypothesis for preserving the oxygen supply/demand relationship is attractive, it does not appear to operate during physiological conditions in the normal heart, since adenosine receptor inhibition does not decrease coronary blood flow or impair the increase of coronary flow during exercise.3 Implicit in the adenosine hypothesis is the assumption that during increased cardiac work, increases of cytosolic free [ADP] would be required to drive mitochondrial respiration and would serve to increase adenosine production. In fact, over a wide range of workloads, cytosolic free [ADP] remains at a stable low level; only at extreme workloads does ADP rise significantly in the normal heart.4 Although it has been difficult to demonstrate adenosine effects during normal physiological conditions, adenosine is clearly able to exert important effects …

Molecular characterization of six unrelated Italian patients affected by pyrimidine 5'-nucleotidase deficiency.

Pyrimidine 5'-nucleotidase deficiency is a rare autosomal recessive disorder characterized by haemolytic anaemia, marked basophilic stippling and accumulation of pyrimidine nucleotides within the erythrocytes. The gene encoding for this enzyme (P5'N-1) has been cloned recently, and seven mutations have so far been identified in 11 unrelated families. We describe the haematological and molecular characteristics of six unrelated Italian patients affected by pyrimidine 5'-nucleotidase deficiency (one from northern and five from southern Italy). The sequence of the complete P5'N-1 gene showed the presence of four different new mutations: a missense mutation AAT-AGT at codon 190 (Asn-Ser), one splicing mutation (IVS9-1 g-c) and two frameshift mutations, DelG576 and InsGG743. Although the molecular defect was homozygous in all patients but one, parents' consanguinity could be confirmed in only one case. InsGG743 was detected in two cases, and DelG576 was found in three patients originating from southern Italy, suggesting a possible geographical distribution of the genetic defect. Haematological data showed the presence of peripheral spherocytosis in all cases, although only one had a concomitant membrane defect. An increase in serum ferritin levels was observed in the splenectomized patients, suggesting that the iron status of these subjects should be monitored and that they should be investigated for potential additional risk factors for iron accumulation.

Pyrimidine 5' nucleotidase deficiency.

Pyrimidine 5' nucleotidase deficiency.

Genetic basis of hemolytic anemia caused by pyrimidine 5′ nucleotidase deficiency

Pyrimidine 5' nucleotidase (P5'N-1) deficiency is an autosomal recessive condition causing hemolytic anemia characterized by marked basophilic stippling and the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. It is implicated in the anemia of lead poisoning and is possibly associated with learning difficulties. Recently, a protein with P5'N-1 activity was analyzed and a provisional complementary DNA (cDNA) sequence published. This sequence was used to study 3 families with P5'N-1 deficiency. This approach generated a genomic DNA sequence that was used to search GenBank and identify the gene for P5'N-1. It is found on chromosome 7, consists of 10 exons with alternative splicing of exon 2, and produces proteins 286 and 297 amino acids long. Three homozygous mutations were identified in this gene in 4 subjects with P5'N-1 deficiency: codon 98 GAT-->GTT, Asp-->Val (linked to a silent polymorphism codon 92, TAC-->TAT), codon 177, CAA-->TAA, Gln-->termination, and IVS9-1, G-->T. The latter mutation results in the loss of exon 9 (201 bp) from the cDNA. None of these mutations was found in 100 normal controls. The DNA analysis was complicated by P5'N-1 pseudogenes found on chromosomes 4 and 7. This study is the first description of the structure and location of the P5'N-1 gene, and 3 mutations have been identified in affected patients from separate kindreds. (Blood. 2001;97:3327-3332)

Chronic non-spherocytic haemolytic anaemia due to congenital pyrimidine 5′ nucleotidase deficiency: 25 years later

In 1972, Valentine et al described, under the name of ‘non-spherocytic haemolytic anaemia, high red cell ATP and ribose phosphate pyrophosphokinase (RPK; EC 2.7.6.1) deficiency’, an obscure congenital haemolytic anaemia with the characteristic feature of red blood cell basophilic stippling. The activity of Embden–Meyerhof pathway and hexose monophosphate shunt were normal, and the concentrations of reduced glutathione and of ATP were raised 2 SD above the normal mean. The low values of RPK also encountered were considered to be an epiphenomenon rather than a causative defect. One year later, further studies performed in two new kindreds with the same haemolytic disorder associated with persistent basophilic stippling were described under the name of ‘haemolytic disorders associated with increased ATP’. In 1974, two new and important observations contributed to the final identification of the disease: the patients' red blood cells (RBCs) contained large amounts of nucleotides (pyrimidine nucleotides), and in all cases they were deficient in a hitherto unrecognized enzyme called pyrimidine 5′ nucleotidase (P5N). In conclusion, all these cases were formerly referred to as ‘high ATP syndromes’ because of the erroneous assumption that the large number of nucleotides within deficient RBCs were adenine phosphate rather than pyrimidine phosphate. Twenty-five years after its description, P5N deficiency has been reported in about 35 unrelated families from different parts of the world, and it has become one commonly identified cause of hereditary non-spherocytic haemolytic anaemia due to RBC enzymopathy. Genetic transmission is via the autosomic recessive mode, and only homozygous or compound heterozygous are clinically affected. Family members who are biochemically heterozygous are haematologically normal and difficult to detect. Unfortunately, the precise gene mutation or mutations causing the disease remain unknown.