Recent progress in the molecular genetic analysis of erythroenzymopathy

Congenital anemia reveals distinct targeting mechanisms for master transcription factor GATA1

Master regulators, such as the hematopoietic transcription factor (TF) GATA1, play an essential role in orchestrating lineage commitment and differentiation. However, the precise mechanisms by which such TFs regulate transcription through interactions with specific cis-regulatory elements remain incompletely understood. Here, we describe a form of congenital hemolytic anemia caused by missense mutations in an intrinsically disordered region of GATA1, with a poorly understood role in transcriptional regulation. Through integrative functional approaches, we demonstrate that these mutations perturb GATA1 transcriptional activity by partially impairing nuclear localization and selectively altering precise chromatin occupancy by GATA1. These alterations in chromatin occupancy and concordant chromatin accessibility changes alter faithful gene expression, with failure to both effectively silence and activate select genes necessary for effective terminal red cell production. We demonstrate how disease-causing mutations can reveal regulatory mechanisms that enable the faithful genomic targeting of master TFs during cellular differentiation.

A Case Report of Congenital Non-spherocytic Hemolytic Anemia in a Patient from India

Congenital non-spherocytic hemolytic anemia (CNSHA) is a rare autosomal recessive condition that presents as a congenital hemolytic anemia. The absence of vital enzymes required for glycolysis such as homozygous glucose phosphate isomerase (GPI) and red blood cell (RBC) nucleotide metabolism predisposes the RBCs to hemolysis. No spherocytosis is seen on peripheral smear as well as no signs of immune-mediated destruction of RBCs. We present a rare case of a previously healthy 21-year-old female patient with CNSHA from India.

Identification of a novel promoter mutation in the human pyruvate kinase (PK) LR gene of a patient with severe haemolytic anaemia

Using direct sequencing we analysed the pyruvate kinase (PK) LR gene of a patient with severe haemolytic anaemia due to PK deficiency. A novel promoter mutation -249delA relative to the translation initiation site and the common 1529A mutation in exon 11 of the gene could be identified. Reverse transcription (RT)-PCR analysis combined with restriction digestion revealed that the -249delA mutation leads to a reduction in the amount of mRNA produced from this allele to about 6% of normal. We assume that both mutations would account for the PK deficiency in the compound heterozygous patient.

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.

Erythrocyte pyruvate kinase- and glucose phosphate isomerase deficiency: perturbation of glycolysis by structural defects and functional alterations of defective enzymes and its relation to the clinical severity of chronic hemolytic anemia

The pathogenesis of two metabolic disorders caused by enzyme defects in the red blood cell leading to hemolytic anemia, and in some cases of glucose phosphate isomerase (GPI) deficiency additionally to neurological impairment was investigated. Rheological studies were performed to determine the influence of a shortage of energy on the deformability of the erythrocytes. The functions of the enzymes were determined by studying the enzyme kinetics, the temperature dependence of the enzyme activity and the migration of the proteins in an electric field. A detailed molecular genetic analysis of the gene encoding for the given protein allowed the detection of mutations involving amino acid exchanges which cause alterations of the protein structure. For both enzyme deficiencies, a good correlation was found between the structural changes (usually caused by single point mutations in the gene), the altered function of the enzymes and the severity of the clinical picture. The exchange of amino acids close to either the active site or the regulatory domain results in a decreased turnover as well as an alteration of the regulatory properties of the enzymes; this usually leads to an increased severity of the disease. Increased concentrations of glucose-6-phosphate (G-6-P), found in all red blood cells of patients suffering from hemolytic anemia caused by pyruvate kinase (PK) and GPI deficiency, correlate well with the severity of the clinical picture, apparently reflecting the degree of the perturbation of glycolysis. This results in a lack of the energy donor adenosine triphosphate (ATP); this leads then to a destabilization of the red cell membrane which causes earlier lysis of the red blood cell, which in turn gives rise to hemolytic anemia of variable degrees. One patient with neurological symptoms has been studied so far biochemically and at the molecular genetic level. The point mutations found in this patient's GPI gene support the idea that GPI may have a neurological function in addition to its role in the carbohydrate metabolism; this is due to the presence of a monomeric sequence analogue called neuroleukin (NLK). The mutations apparently lead to the incorrect folding of this neurotrophic factor, and thus destroy the neurological activity.

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.

Sequence characterization of alleles Gpi1-Sa and Gpi1-Sb at the glucose phosphate isomerase structural locus

The sequences of alleles Gpi1-sa and Gpi1-sb at the glucose phosphate isomerase structural locus have been determined from cDNA of the mouse inbred strains 101/H Gpi1-sa and C3H/HeH Gpi1-sb by RT PCR and direct sequencing of the amplified products. Four individual nucleotide differences were observed between the two alleles. The difference at amino acid residue 94, (Gpi1-sa GAT Asp, Gpi1-sb AAT Asn) may account for the differing electrophoretic migration, isoelectric point, and thermostability of the two alleles. Two of the other observed differences in the coding region (amino acid residue 12 Leu, Gpi1-sa CTC, Gpi1-sb CTG and amino acid residue 17 Arg, Gpi1-sa CGC, Gpi1-sb CGT) are silent and do not affect the predicted amino acid residues on translation. The fourth observed difference is located within the 3' noncoding sequences of the cDNA. The change at amino acid residue 94 is associated with the presence of a Hinf1 restriction site in Gpi1-sb, which is absent in Gpi1-sa, and may be a useful method for determining this marker.

Triosephosphate isomerase deficiency: biochemical and molecular genetic analysis for prenatal diagnosis

Inherited deficiency of the glycolytic enzyme triosephosphate isomerase leads to a multisystem disorder characterized by progressive neuromuscular dysfunction, chronic nonspherocytic hemolytic anemia and increased susceptibility to severe infections. Most patients die within the first 6 years. We examined a family with severe triosephosphate isomerase deficiency. The 1-year-old index patient suffered from hemolytic anemia, neuromuscular impairment and pneumonias, with the necessity of intermitten mechanical ventilation. Triosephosphate isomerase activity in erythrocytes was reduced to about 20% of normal. Heat stability of the enzyme was strongly reduced; concentration of the physiological substrate, dihydroxyacetone phosphate was increased 20-fold due to the metabolic block. Direct sequencing of the triosephosphate isomerase gene revealed homozygosity for the formerly described GAG-->GAC-mutation changing 104 Glu-->Asp. During a 2nd pregnancy we examined a cord blood sample obtained in the 19th gestational week. The biochemical data on enzyme activity, heat stability of the enzyme and concentration of dihydroxyacetone phosphate were in the normal range. The molecular genetic analysis confirmed the presence of the normal triosephosphate isomerase alleles. Pregnancy was continued, resulting in the delivery of an unaffected, healthy newborn.

The characterization of gene mutations for human glucose phosphate isomerase deficiency associated with chronic hemolytic anemia

DNA was isolated from four unrelated glucose phosphate isomerase-deficient patients. Seven new mutations in the coding region were found: 247 C-->T, 671 C-->T, 818 G-->A, 833 C-->T, 1039 C-->T, 1459 C-->T, and 1483 G-->A. Three patients were compound heterozygotes, and one patient was a homozygote of 247 C-->T/247 C-->T. Six mutations were found to involve highly conserved amino acids of glucose phosphate isomerase, suggesting that these residues are crucial for the maintenance of biological activity. Two polymorphic sites were also identified, 489 A-->G and 1356 G-->C, which do not produce a change in the amino acid sequence.

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.

Glucose phosphate isomerase (GPI) "Morcone": a new variant from Italy

Here we report the 4th Italian case of glucose phosphate isomerase (GPI) deficiency. The propositus is a young man suffering from chronic haemolytic anaemia since birth with occasional transfusion requirement. Biochemical characterization of the defective enzyme revealed increased affinity for F-6-P, decreased affinity for G-6-P and marked thermoinstability. Electrophoretic mobility appeared normal. GPI from both parents showed similar but less pronounced biochemical alterations. The variant described here seems to be different from those previously reported. Thus, we propose the provisional name of GPI "Morcone".