Molecular basis of impaired pyruvate kinase isozyme conversion in erythroid cells: a single amino acid substitution near the active site and decreased mRNA content of the R-type PK

Clinical outcome and genotype analysis of four Chinese children with pyruvate kinase deficiency

BACKGROUND

Pyruvate kinase deficiency (PKD) is a rare congenital hemolytic anemia. Here, we summarized the clinical features and laboratory examinations of four Chinese children with PKD and analyze genomic mutations.

METHOD

Collected and analyzed the clinical data of all children and their parents and completed the relevant laboratory examinations of all children. Analyzed the sequences of related genes in children by second-generation sequencing technology and verified the suspected mutations in children's family by Sanger sequencing method or second-generation sequencing technology.

RESULTS

A total of six mutations in gene PKLR were detected in four cases. Except for c.1510C>T (P1) and c.941T>C (P2 and P4), which had been reported in previous studies, the other four novel gene mutations were reported for the first time, including a rare homozygous mutation with large fragment deletion. All those gene mutations cause changes in the amino acids encoded by the gene, as well as subsequent changes in protein structure or loss of function.

CONCLUSION

Compound heterozygous or homozygous mutations in the coding region of PKLR gene are the causes of PKD in these four Chinese children. The second-generation sequencing technology is an effective means to diagnose PKD. The mutations of c.457-c.462delATCGCC, c.1297T>C, c.1096C>T and Exon4-10del of PKLR reported in this article have not been included in the Thousand Genome Database, dbSNP(v138) and ExAC Database. The PKLR gene mutations found in these children with PKD can provide references for further research of the genetic characteristics of PKD and subsequent gene therapy.

PYK-SubstitutionOME: an integrated database containing allosteric coupling, ligand affinity and mutational, structural, pathological, bioinformatic and computational information about pyruvate kinase isozymes

Interpreting changes in patient genomes, understanding how viruses evolve and engineering novel protein function all depend on accurately predicting the functional outcomes that arise from amino acid substitutions. To that end, the development of first-generation prediction algorithms was guided by historic experimental datasets. However, these datasets were heavily biased toward substitutions at positions that have not changed much throughout evolution (i.e. conserved). Although newer datasets include substitutions at positions that span a range of evolutionary conservation scores, these data are largely derived from assays that agglomerate multiple aspects of function. To facilitate predictions from the foundational chemical properties of proteins, large substitution databases with biochemical characterizations of function are needed. We report here a database derived from mutational, biochemical, bioinformatic, structural, pathological and computational studies of a highly studied protein family-pyruvate kinase (PYK). A centerpiece of this database is the biochemical characterization-including quantitative evaluation of allosteric regulation-of the changes that accompany substitutions at positions that sample the full conservation range observed in the PYK family. We have used these data to facilitate critical advances in the foundational studies of allosteric regulation and protein evolution and as rigorous benchmarks for testing protein predictions. We trust that the collected dataset will be useful for the broader scientific community in the further development of prediction algorithms. Database URL https://github.com/djparente/PYK-DB.

Red blood cell PK deficiency: An update of PK-LR gene mutation database

Pyruvate kinase (PK) deficiency is known as being the most common cause of chronic nonspherocytic hemolytic anemia (CNSHA). Clinical PK deficiency is transmitted as an autosomal recessive trait, that can segregate neither in homozygous or in a compound heterozygous modality, respectively. Two PK genes are present in mammals: the pyruvate kinase liver and red blood cells (PK-LR) and the pyruvate kinase muscle (PK-M), of which only the first encodes for the isoenzymes normally expressed in the red blood cells (R-type) and in the liver (L-type). Several reports have been published describing a large variety of genetic defects in PK-LR gene associated to CNSHA. Herein, we present a review of about 250 published mutations and six polymorphisms in PK-LR gene with the corresponding clinical and molecular data. We consulted the PubMed website for searching mutations and papers, along with two main databases: the Leiden Open Variation Database (LOVD, https://grenada.lumc.nl/LOVD2/mendelian_genes/home.php?select_db=PKLR) and Human Gene Mutation Database (HGMD, http://www.hgmd.cf.ac.uk/ac/gene.php?gene=PKLR) for selecting, reviewing and listing the annotated PK-LR gene mutations present in literature. This paper is aimed to provide useful information to clinicians and laboratory professionals regarding overall reported PK-LR gene mutations, also giving the opportunity to harmonize data regarding PK-deficient individuals.

Rescue of pyruvate kinase deficiency in mice by gene therapy using the human isoenzyme

Human erythrocyte R-type pyruvate kinase deficiency (PKD) is a disorder caused by mutations in the PKLR gene that produces chronic nonspherocytic hemolytic anemia. Besides periodic blood transfusion and splenectomy, severe cases require bone marrow (BM) transplant, which makes this disease a good candidate for gene therapy. Here, the normal human R-type pyruvate kinase (hRPK) complementary (cDNA) was expressed in hematopoietic stem cells (HSCs) derived from pklr deficient mice, using a retroviral vector system. These mice show a similar red blood cell phenotype to that observed in human PKD. Transduced HSCs were transplanted into myeloablated adult PKD mice or in utero injected into nonconditioned PKD fetuses. In the myeloablated recipients, the hematological manifestations of PKD were completely resolved and normal percentages of late erythroid progenitors, reticulocyte and erythrocyte counts, hemoglobin levels and erythrocyte biochemistry were restored. Corrected cells preserved their rescuing capacity after secondary and tertiary transplant. When corrected cells were in utero transplanted, partial correction of the erythrocyte disease was obtained, although a very low number of corrected cells became engrafted, suggesting a different efficiency of cell therapy applied in utero. Our data suggest that transduction of human RPK cDNA in PKLR mutated HSCs could be an effective strategy in severe cases of PKD.

In vitro and in vivo expression of human erythrocyte pyruvate kinase in erythroid cells: a gene therapy approach

Human pyruvate kinase deficiency (PKD), an autosomal recessive disorder produced by mutations in the PKLR gene, is the most common cause of chronic nonspherocytic hemolytic anemia. Transduction of wild-type erythroid (R-type) pyruvate kinase (RPK) cDNA into deficient hematopoietic stem cells could be of potential use as rescue therapy in severe clinical cases. In this study, gammaretroviral vectors expressing human RPK were designed as possible gene therapy candidates for this disease. Through real-time quantitative reverse transcriptase-polymerase chain reaction, Western blotting, and flow cytometric analysis, we demonstrate stable RPK expression in both undifferentiated and differentiated murine erythroleukemia cells. In this in vitro assay, the proportion of transduced cells and the intensity of expression of the transgene remained unaltered after 6 months of culture. Moreover, transplanting human RPK-transduced Lin(-)Sca-1(+) mouse cells in myeloablated primary and secondary recipients rendered high proportions of erythroid precursors and mature erythrocytes expressing RPK, without inducing hematopoietic effects. These findings suggest that retroviral vectors could be useful for the delivery and expression of RPK in erythroid cells, and provide evidence of the potential use of gene therapy strategies to phenotypically correct erythroid PKD.

Pyruvate kinase deficiency: the genotype-phenotype association

Red cell pyruvate kinase (PK) deficiency is the most frequent enzyme abnormality of glycolysis causing chronic non-spherocytic haemolytic anaemia. The disease is transmitted as an autosomal recessive trait, clinical symptoms usually occurring in compound heterozygotes for two mutant alleles and in homozygotes. The severity of haemolysis is highly variable, ranging from very mild or fully compensated forms to life-threatening neonatal anaemia necessitating exchange transfusions. Erythrocyte PK is synthesised under the control of the PK-LR gene located on chromosome 1. One hundred eighty different mutations in PK-LR gene, mostly missense, have been so far reported associated to PK deficiency. First attempts to delineate the genotype-phenotype association were mainly based on the analysis of the enzyme's three-dimensional structure and the observation of the few homozygous patients. More recently, the comparison of the recombinant mutants of human red cell PK with the wild-type enzyme has enabled the effects of amino acid replacements on the enzyme molecular properties to be determined. However, the clinical manifestations of red cell enzyme defects are not merely dependent on the molecular properties of the mutant protein but rather reflect the complex interactions of additional factors, including genetic background, concomitant functional polymorphisms of other enzymes, posttranslational or epigenetic modifications, ineffective erythropoiesis and differences in splenic function.

Red cell pyruvate kinase deficiency: molecular and clinical aspects

Red cell pyruvate kinase (PK) deficiency is the most frequent enzyme abnormality of the glycolytic pathway causing hereditary non-spherocytic haemolytic anaemia. The degree of haemolysis varies widely, ranging from very mild or fully compensated forms, to life-threatening neonatal anaemia and jaundice necessitating exchange transfusions. Erythrocyte PK is synthesized under the control of the PK-LR gene located on chromosome 1. To date, more than 150 different mutations in the PK-LR gene have been associated with PK deficiency. First attempts to delineate the biochemical and clinical consequences of the molecular defect were mainly based on the observation of the few homozygous patients and on the analysis of the three-dimensional structure of the enzyme. More recently, the comparison of the recombinant mutants of human red cell PK 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.

Life-threatening nonspherocytic hemolytic anemia in a patient with a null mutation in the PKLR gene and no compensatory PKM gene expression

Human erythrocyte R-type pyruvate kinase (RPK) deficiency is an autosomal recessive disorder produced by mutations in the PKLR gene, causing chronic nonspherocytic hemolytic anemia. Survival of patients with severe RPK deficiency has been associated with compensatory expression in red blood cells (RBCs) of M2PK, an isoenzyme showing wide tissue distribution. We describe a novel homozygous null mutation of the PKLR gene found in a girl with a prenatal diagnosis of PK deficiency. The mutant PK gene revealed an 11-nucleotide (nt) duplication at exon 8, causing frameshift of the PKLR transcript, predicting a truncated protein inferred to have no catalytic activity. Western blot analysis and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) detected no M2PK expression in the peripheral blood red cell fraction. The expression of mutant RPK mRNA in the RBCs was almost 6 times higher than that detected in a control patient with hereditary spherocytosis. This molecular phenotypic analysis of the null mutation in the PKLR gene provides evidence for a lack of M2PK in the mature RBCs of this patient and suggests that normal red cell functions and survival are achieved through a population of young erythroid cells released into the circulation in response to anemia. (Blood. 2005;106:1851-1856)

Novel mutations and structural implications in R-type pyruvate kinase-deficient patients from Southern Italy

Deficiency of the R-type pyruvate kinase (R-PK) causes an autosomal recessive, hereditary, nonspherocytic hemolytic anemia (HNSHA). We screened seven unrelated patients from the south of Italy for the known mutations and found one patient homozygous for the 1529A (R510Q) mutation, two others bearing the 1456T (R486W) mutation, one homozygous and another heterozygous, and two heterozygotes for the 994A mutation (G332S). We also found three novel mutations at the heterozygote status: a G to C transversion in position 1010 (1010C; R337P) and a C to T transition in position 1492 (1492T; R498C), which are missense, and a T to G transversion in position 1523 (1523G; L508Z), which produces a stop codon with a subsequent loss of the C-terminal protein domain. The structural features of R-PK in the mutation-bearing regions were examined. In all cases the mutations altered the local conformation of the enzyme. Both G332S and R337P are in highly conserved sequence regions. In particular, the R337P mutation significantly affects the intersubunit interactions, because it is located in a region subjected to a large conformational change that occurs during the R-->T allosteric transition, which is essential for the enzyme activity. The R486W mutation affects an external pocketlike region, producing only a local conformational change; the R498C mutation changes the interactions among neighbouring residues; the R510Q mutation involves the loss of interdomain interactions that may reduce enzyme stability and activity. Our data also indicate that in patients from Southern Italy, pyruvate kinase deficiency is heterogeneous, the 1529A mutation, which is the most frequent mutation in the U.S. Caucasian population, having a lower frequency.

Red cell pyruvate kinase deficiency: from genetics to clinical manifestations

Pyruvate kinase deficiency is the most frequent enzyme abnormality of the Embden-Meyerhof pathway causing hereditary non-spherocytic haemolytic anaemia. The degree of haemolysis varies widely, ranging from very mild or fully compensated forms, to life-threatening neonatal anaemia and jaundice necessitating exchange transfusions. Splenectomy should be reserved for young patients who require regular blood transfusions. The gene encoding for pyruvate kinase (PK-LR) has been localized to the long arm of chromosome I; the cDNA of R-type is 2060 bp long and codes for 574 amino acids. More than 130 different mutations, mostly missense, have so far been described in association with PK deficiency, 1529A and 1456T being considered to be the most common mutations in Caucasians. Analysis of the three-dimensional structure of the enzyme may help in predicting the severity of the molecular defect. Further data on clinical features of homozygous patients are needed, at least for some mutations, to allow a more precise genotype/phenotype correlation.

PK-LR gene mutations in pyruvate kinase deficient Portuguese patients

In nine unrelated Portuguese patients with pyruvate kinase (PK) deficient anaemia, whose symptoms ranged from a mild chronic haemolytic anaemia to a severe anaemia presenting at birth and requiring multiple transfusions, the PK-LR gene mutations were identified and correlated with their phenotypes. Five different mutations were identified, three of them for the first time: a missense mutation 1670G --> C on exon 12 and two 5' splice donor site (GT) mutations on intron 8 [IVS8(+2)T --> G] and intron 10 [IVS10(+1)G --> C]. Two previously described missense mutations, 1456C --> T and 993C --> A, were also found. The genotype/phenotype correlation showed that patients with two missense mutations or with a missense mutation and a splicing mutation had a mild haemolytic anaemia. The three patients with severe anaemia, who were transfusion dependent until splenectomy, were homozygous for the splicing site mutations IVS10(+1)G --> C or IVS8(+2)T --> G.

Red blood cell enzymes and their clinical application

Red blood cell enzyme activities are measured mainly to diagnose hereditary nonspherocytic hemolytic anemia associated with enzyme anomalies. At least 15 enzyme anomalies associated with hereditary hemolytic anemia have been reported. Some nonhematologic disease can also be diagnosed by the measurement of red blood cell enzyme activities in the case in which enzymes of red blood cells and the other organs are under the same genetic control. Progress in molecular biology has provided a new perspective. Techniques such as the polymerase chain reaction and single-strand conformation polymorphism analysis have greatly facilitated the molecular analysis of erythroenzymopathies. These studies have clarified the correlation between the functional and structural abnormalities of the variant enzymes. In general, the mutations that induce an alteration of substrate binding site and/or enzyme instability might result in markedly altered enzyme properties and severe clinical symptoms.

Molecular characterization of the PK-LR gene in pyruvate kinase deficient Spanish patients. Red Cell Pathology Group of the Spanish Society of Haematology (AEHH)

The PK-LR gene has been studied in 12 unrelated patients with red cell pyruvate kinase deficiency and hereditary nonspherocytic haemolytic anaemia (CNSHA). The entire codifying region of the R-type PK gene and the flanking intronic regions were analysed by single-stranded conformation polymorphism (SSCP) followed by direct sequencing of abnormal DNA. 10 different mutations were identified in 22/24 alleles at risk. Eight of these were missense mutations that caused the following single amino acid changes: G514C (172Glu-Gln), G1010A (337Arg-Gln), G1015C (339Asp-Gln), T1070C (357Ile-Thr), C1223T (408Thr-Ile), G1291A (431Ala-Thr), C1456T (486Arg-Trp) and G1595A (532Arg-Gln). Two were nonsense mutations: G721T (241Glu-Stop) and C1675T (559Arg-Stop). 7/22 alleles demonstrated the same C1456 --> T mutation. The study of the polymorphic site at nucleotide (nt) 1705 performed in all cases disclosed a 1705 C/C mutation in 10 and a 1705 A/C mutation in three. This is the first report on the presence of several different L-type PK gene mutations within Spanish population. Furthermore, from the PK gene mutations found, six were unique and not previously described (1015C, 1070C, 1223T, 1291A, 1595A and 1675T) and one (C1456T) seems to be predominant in Spain. Interestingly, no case with the 1529A mutation commonly found in Northern European populations was present here.

Molecular Characterization of PK-LR Gene in Pyruvate Kinase–Deficient Italian Patients

We studied the PK-LR gene in 15 unrelated Italian patients with congenital hemolytic anemia associated with erythrocyte pyruvate kinase (PK) deficiency. Fourteen different mutations were detected among 26 mutated alleles identified: a five-nucleotide (nt) deletion (227 to 231), two splice-site (1269C and IVS3(−2)c), 10 missense (514C, 787T, 823A, 993A, 994A, 1168A, 1456T, 1529A, 1552A, and 1594T) and one nonsense mutation(s) (721T). Eight of these (deletion 227-231, 1269C, IVS3(−2)c, 514C, 787T, 823A, 1168A, and 1552A) were novel. Moreover, a new polymorphic site was detected in the 3′ untranslated region of the mRNA (C/T, nucleotide 1738). The deletion 227-231 causes a stop codon after amino acid 77, probably resulting in an unstable gene product. Mutations 1269C and IVS3(−2)c lead to an alteration of the 5′ and 3′ splice-site consensus sequence, respectively; cDNA analysis failed to reveal any abnormal transcript, suggesting that these mutations generate an unstable mRNA that is rapidly degraded. Of the five new missense mutations, 823A (Gly275-Arg) and 1168A (Asp390-Asn) involve highly conserved amino acids, 514C (Glu172-Gln) and 1552A (Arg518-Ser), although found in less conserved regions, affect the balance of the electric charges of the protein. Mutation 787T (Gly263-Trp) is likely to determine strong modifications in the local structure of the molecule. The most frequent mutation in Italy appears to be 1456T (seven of 30 alleles), followed by 1529A (three of 30) and 994A (three of 30). A correlation was found between mutations, biochemical characteristics of the enzyme, and clinical course of the disease.

Molecular Characterization of PK-LR Gene in Pyruvate Kinase–Deficient Italian Patients

We studied the PK-LR gene in 15 unrelated Italian patients with congenital hemolytic anemia associated with erythrocyte pyruvate kinase (PK) deficiency. Fourteen different mutations were detected among 26 mutated alleles identified: a five-nucleotide (nt) deletion (227 to 231), two splice-site (1269C and IVS3(−2)c), 10 missense (514C, 787T, 823A, 993A, 994A, 1168A, 1456T, 1529A, 1552A, and 1594T) and one nonsense mutation(s) (721T). Eight of these (deletion 227-231, 1269C, IVS3(−2)c, 514C, 787T, 823A, 1168A, and 1552A) were novel. Moreover, a new polymorphic site was detected in the 3′ untranslated region of the mRNA (C/T, nucleotide 1738). The deletion 227-231 causes a stop codon after amino acid 77, probably resulting in an unstable gene product. Mutations 1269C and IVS3(−2)c lead to an alteration of the 5′ and 3′ splice-site consensus sequence, respectively; cDNA analysis failed to reveal any abnormal transcript, suggesting that these mutations generate an unstable mRNA that is rapidly degraded. Of the five new missense mutations, 823A (Gly275-Arg) and 1168A (Asp390-Asn) involve highly conserved amino acids, 514C (Glu172-Gln) and 1552A (Arg518-Ser), although found in less conserved regions, affect the balance of the electric charges of the protein. Mutation 787T (Gly263-Trp) is likely to determine strong modifications in the local structure of the molecule. The most frequent mutation in Italy appears to be 1456T (seven of 30 alleles), followed by 1529A (three of 30) and 994A (three of 30). A correlation was found between mutations, biochemical characteristics of the enzyme, and clinical course of the disease.

Molecular Analysis of 29 Pyruvate Kinase–Deficient Patients From Central Europe With Hereditary Hemolytic Anemia

We investigated the DNA of 29 unrelated pyruvate kinase (PK) deficiency (PKD) patients from Central Europe with hereditary nonspherocytic hemolytic anemia for mutations in the PK-L/R gene. Among 58 potentially affected alleles, 53 mutations were identified, of which 17 were different from each other. Of these 17 mutations, 13 were single-nucleotide (nt) substitutions resulting in amino acid exchanges, G787A (Gly263-Arg), G994A (Gly332-Ser), G1006T (Ala336-Ser), G1010A (Arg337-Gln), A1081G (Asn361-Asp), G1127T (Ser376-Ile), G1174A (Ala392-Thr), G1281T (Glu427-Asp), C1454T (Ser485-Phe), C1456T (Arg486-Trp), G1493A (Arg498-His), G1529A (Arg510-Gln), and C1594T (Arg532-Trp); 1 in-frame triplet deletion, 1060delAAG (delLys354); 1 in-frame triplet insertion, 1203insAGC (insSer after Cys401); 1 splicesite mutation, 101-1G-A; and 1 frameshift deletion, 628delGT. Six mutations, 628delGT, G787A, G1010A, G1127T, G1281T, and C1454T, are described for the first time. To test the hypothesis of a single origin of the most common PK mutation in the European population, G1529A, we investigated all patients at four polymorphic sites in the PK-L/R gene: C/A at nt 1705, C/T at nt 1992, the (ATT)n microsatellite in intron J, and a polymorphism (T)10/(T)19 in intron I. Nine patients homozygous for mutation G1529A were consistent in all four markers. In the group of patients homozygous for mutation G1529A, the hematologic parameters and clinical manifestations have been studied in detail. Although having an identical mutation in the PK-L/R gene, the patients are affected differently. Their appearance ranges from a very mild compensated hemolysis to a severe anemia. Possible molecular explanations are discussed.

Molecular Analysis of 29 Pyruvate Kinase–Deficient Patients From Central Europe With Hereditary Hemolytic Anemia

We investigated the DNA of 29 unrelated pyruvate kinase (PK) deficiency (PKD) patients from Central Europe with hereditary nonspherocytic hemolytic anemia for mutations in the PK-L/R gene. Among 58 potentially affected alleles, 53 mutations were identified, of which 17 were different from each other. Of these 17 mutations, 13 were single-nucleotide (nt) substitutions resulting in amino acid exchanges, G787A (Gly263-Arg), G994A (Gly332-Ser), G1006T (Ala336-Ser), G1010A (Arg337-Gln), A1081G (Asn361-Asp), G1127T (Ser376-Ile), G1174A (Ala392-Thr), G1281T (Glu427-Asp), C1454T (Ser485-Phe), C1456T (Arg486-Trp), G1493A (Arg498-His), G1529A (Arg510-Gln), and C1594T (Arg532-Trp); 1 in-frame triplet deletion, 1060delAAG (delLys354); 1 in-frame triplet insertion, 1203insAGC (insSer after Cys401); 1 splicesite mutation, 101-1G-A; and 1 frameshift deletion, 628delGT. Six mutations, 628delGT, G787A, G1010A, G1127T, G1281T, and C1454T, are described for the first time. To test the hypothesis of a single origin of the most common PK mutation in the European population, G1529A, we investigated all patients at four polymorphic sites in the PK-L/R gene: C/A at nt 1705, C/T at nt 1992, the (ATT)n microsatellite in intron J, and a polymorphism (T)10/(T)19 in intron I. Nine patients homozygous for mutation G1529A were consistent in all four markers. In the group of patients homozygous for mutation G1529A, the hematologic parameters and clinical manifestations have been studied in detail. Although having an identical mutation in the PK-L/R gene, the patients are affected differently. Their appearance ranges from a very mild compensated hemolysis to a severe anemia. Possible molecular explanations are discussed.

PK Mondor: prenatal diagnosis of a frameshift mutation in the LR pyruvate kinase gene associated with severe hereditary non-spherocytic haemolytic anaemia

A mutant form of pyruvate kinase (PK) from the red blood cells of a consanguineous family with severe non-spherocytic haemolytic anaemia has been characterized by polymerase chain reaction (PCR) amplification and sequencing. The variant enzyme was named PK Mondor, according to the recommendations of the International Committee for Standardisation in Haematology. The propositus lacked PK activity and the low level of PK activity found resulted more likely from PK-M2 (fetal isozyme) expression in the red blood cells of the propositus. PK Mondor corresponds to a frameshift mutation with deletion of one G in a repetition of four Gs in positions 1231-1234. This family, whose first child was stillborn and whose second was homozygous for the frameshift mutation, requested prenatal diagnosis during the third pregnancy. Diagnosis was made after chorionic biopsy by a specific approach combining PCR amplification and restriction enzyme digestion.

Molecular basis of erythroenzymopathies associated with hereditary hemolytic anemia: tabulation of mutant enzymes

Molecular abnormalities of erythroenzymopathies associated with hereditary hemolytic anemia have been determined by means of molecular biology. Pyruvate kinase (PK) deficiency is the most common and well-characterized enzyme deficiency in the glycolytic pathway, and it causes hereditary hemolytic anemia. To date, 47 gene mutations have been identified. We identified one base deletion, one splicing mutation, and six distinct missense mutations in 12 unrelated families with a homozygous PK deficiency. Mutations located near the substrate or fructose-1,6- diphosphate binding site may change the conformation of the active site, resulting in a drastic loss of activity and severe clinical symptoms. Glucose-6-phosphate dehydrogenase (G6PD)deficiency is the most common metabolic disorder, and it is associated with chronic hemolytic anemia and/or drug- or infection-induced acute hemolytic attack. An estimated 400 million people are affected worldwide. The mutations responsible for about 78 variants have been determined. Some have polymorphic frequencies in different populations. Most variants are produced by one or two nucleotide substitutions. Molecular studies have disclosed that most of the class 1 G6PD variants associated with chronic hemolysis have the mutations surrounding either the substrate or the NADP binding site. Among rare enzymopathies, missense mutations have been determined in deficiencies of glucosephosphate isomerase, (TPI), phosphoglycerate kinase, and adenylate kinase. Compound heterozygosity with missense mutation and base deletion has been determined in deficiencies of hexokinase and diphosphoglyceromutase. Compound heterozygosity with missense and nonsense mutations has been identified in TPI deficiency. One base junction mutations resulting in abnormally spliced PFK-M mRNA have been identified in homozygous PFK deficiency. An exception is hemolytic anemia due to increased adenosine deaminase activity. The basic abnormality appears to result from the overproduction of a structurally normal enzyme.

Mutations in pyruvate kinase

Pyruvate kinase (PK) deficiency due to mutations of the PKLR gene is a common cause of hereditary nonspherocytic hemolytic anemia. Thus far, 55 different mutations have been described in patients with PK-deficient hemolytic anemia. Polymorphisms within the PKLR gene and in the tightly linked glucocerebrosidase (GBA) gene suggest that PK deficiency may represent a balanced polymorphism.

Molecular study of pyruvate kinase deficient patients with hereditary nonspherocytic hemolytic anemia

DNA analysis was performed on 30 unrelated patients with hereditary nonspherocytic hemolytic anemia (HNSHA) who had been found to be pyruvate kinase (PK) deficient by enzyme assay. 19 different mutations were identified among 58 of the 60 alleles at risk. 13 of these were missense mutations that caused single amino acid changes. Included were the following nucleotide substitutions: 401A, 464C, 993A, 1022C, 1076A, 1178G, 1179A, 1373A, 1378A, 1456T, 1484T, 1493A, 1529A. The remaining six mutations were as follows: two nonsense mutations, 721T and 808T; a nucleotide deletion, 307C; a nucleotide insertion, 1089GG; a three nucleotide in frame deletion, 391-392-393 and a deletion of 1149 bp from the PKLR gene that resulted in the loss of exon 11. All the patients were studied for two polymorphic sites, nucleotide (nt) 1705 A/C and a microsatellite in intron 11, to better understand the origin of the mutations. The 1529A mutation, which is the most common mutation in the European population, was found in 25 alleles. With a single exception this mutation was in linkage disequilibrium with both of the polymorphic markers, i.e., found with 1705C and 14 repeats in the microsatellite. This finding is consistent with a single origin of this common mutation. Other mutations occurring more than once were of much lower frequency than the 1529A mutation.

Mutations in the R-type pyruvate kinase gene and altered enzyme kinetic properties in patients with hemolytic anemia due to pyruvate kinase deficiency

The biochemical properties of erythrocyte pyruvate kinase (PK) together with mutations found in the coding sequence of the R-PK gene in five patients with severe hemolytic anemia due to PK deficiency are described. The enzyme variants were designated PK 'Mosul' (homozygote), PK 'Bukarest', PK 'Hamburg', PK 'Köln', and PK 'Essen' (compound heterozygote). PK 'Mosul' showed normal positive cooperative substrate binding, PK 'Bukarest' exhibited non-cooperative behavior, and PK 'Hamburg' and PK 'Köln' displayed mixed cooperativity, whereas PK 'Essen' was negative cooperative. PK 'Mosul' was found to be homozygous for the mutation 1151 ACG to ATG, resulting in an amino acid substitution 384 Thr to Met. In one allele of PK 'Bukarest' a single nucleotide substitution GAG-TAG was found at nucleotide 721, causing a change of 241 Glu to a chain termination codon (PK 'Bukarest'). Additionally, in the second allele of this patient a point mutation at position 1594 (CGG-TGG) occurs, changing 532 Arg to Trp (PK 'Bukarest'). Direct sequencing showed the heterozygosity of the patient's mother (PK 'Bukarest'/normal) at position 721 and of the patient's father (PK 'Bukarest'/normal) at position 1594. A point mutation at position 1529 (CGA-CAA), causing an amino acid substitution 510 Arg-Gln, was identified in PK 'Hamburg' and PK 'Köln'. The second mutation in these variants was not detected. In PK 'Essen' no mutation in the coding sequence was found at all. Screening for the mutation at position 1529 in further compound heterozygote patients and in normal subjects of Western European origin showed that this exchange is a common mutation responsible for PK deficiency in this population.