Targeted next-generation sequencing identifies eighteen novel mutations expanding the molecular and clinical spectrum of PKLR gene disorders in the Indian population

Pyruvate kinase deficiency (PKD) is an autosomal recessive condition, caused due to homozygous or compound heterozygous mutation in the PKLR gene resulting in non-spherocytic hereditary hemolytic anemia. Clinical manifestations in PKD patients vary from moderate to severe lifelong hemolytic anemia either requiring neonatal exchange transfusion or blood transfusion support. Measuring PK enzyme activity is the gold standard approach for diagnosis but residual activity must be related to the increased reticulocyte count. The confirmatory diagnosis is provided by PKLR gene sequencing by conventional as well as targeted next-generation sequencing involving genes associated with enzymopathies, membranopathies, hemoglobinopathies, and bone marrow failure disorders. In this study, we report the mutational landscape of 45 unrelated PK deficiency cases from India. The genetic sequencing of PKLR revealed 40 variants comprising 34 Missense Mutations (MM), 2 Nonsense Mutations (NM), 1 Splice site, 1 Intronic, 1 Insertion, and 1 Large Base Deletion. The 17 novel variants identified in this study are A115E, R116P, A423G, K313I, E315G, E318K, L327P, M377L, A423E, R449G, H507Q, E538K, G563S, c.507 + 1 G > C, c.801_802 ins A (p.Asp268ArgfsTer48), IVS9dsA-T + 3, and one large base deletion. In combination with previous reports on PK deficiency, we suggest c.880G > A, c.943G > A, c.994G > A, c.1456C > T, c.1529G > A are the most frequently observed mutations in India. This study expands the phenotypic and molecular spectrum of PKLR gene disorders and also emphasizes the importance of combining both targeted next-generation sequencing with bioinformatics analysis and detailed clinical evaluation to elaborate a more accurate diagnosis and correct diagnosis for transfusion dependant hemolytic anemia in a cohort of the Indian population.

Targeted next-generation sequencing identifies novel deleterious variants in ANK1 gene causing severe hereditary spherocytosis in Indian patients: expanding the molecular and clinical spectrum

Hereditary Spherocytosis (HS) is a common cause of hemolytic anemia varying from mild to severe hemolysis due to defects in red cell membrane protein genes, namely ANK1, SPTB, SPTA1, SLC4A1, and EPB42. These genes are considerably very large spaning 40-50 exons making gene-by-gene analysis costly and laborious by conventional methods. In this study, we explored 26 HS patients harboring 21 ANK1 variants identified by next-generation sequencing (NGS), characteristics and spectrum of the detected ANK1variants were analyzed in this study. Clinically, all the HS patients showed moderate to severe transfusion-dependent hemolytic anemia, some requiring splenectomy. We identified 13 novel and 8 reported variants, mainly 9 frameshifts, 2 missense, 6 nonsense, and 4 splice site ANK1 variants, using NGS technology. Frameshifts were remarkably the most common variant type seen in Indian HS patients with ANK1 gene defects. We have also explored expression levels of red cell membrane ankyrin protein by flow cytometry in 14 HS patients with ANK1 gene defects and a significant reduction in ankyrin protein expression has been found. This report mainly illustrates the molecular and phenotypic heterogeneity of ANK1 variants causing HS in Indian patients. Ankyrin-1 mutations are a significant cause of loss of function in dominant HS in the Indian population. Comprehensive genetic and phenotypic evaluation assists in implementing the knowledge of genetic patterns and spectrum of ANK1 gene variants, providing molecular support for HS diagnosis.

Rare hereditary nonspherocytic hemolytic anemia caused by a novel homozygous mutation, c.301C > A, (Q101K), in the AK1 gene in an Indian family

Background

Adenylate kinase (AK) deficiency is a rare red cell enzymopathy associated with moderate to severe congenital nonspherocytic hemolytic anemia, along with mental and psychomotor retardation (in exceptional cases). Only ten mutations have been detected in the AK1 gene to date. In this study, we aimed to diagnose the unexplained issue of haemolytic anaemia and offer antenatal screening to the family.

Methods

Genomic DNA was isolated from whole blood by a standard protocol. Targeted next-generation sequencing (t-NGS) was performed to identify pathogenic variants in the patient and control samples. A chronic villus sample was collected at 11 weeks of gestation from the mother, and molecular testing was performed. Genetic confirmation was concluded by Sanger DNA sequencing. Bioinformatics tools predicted the pathogenicity of the variant.

Results

t-NGS revealed a homozygous variant (c.301C > A, p. Gln101Lys) in the AK1 gene in the patient and heterozygosity in the fetus and parental samples. The prediction tools SIFT, Polyphen2, Provean, PMUT, Mutation taster, and Mutation Assessor, confirmed the damaging effect of the variant on the AK1 protein structure

Conclusion

We have presented a novel mutation in the AK1 gene (p. Gln101Lys) associated with adenylate kinase deficiency. It is the first prenatal diagnosis of AK deficiency in India, where heterogeneity is exceptionally high.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-01038-2.

Erythrocytes as a preferential target of oxidative stress in blood

Red blood cells (RBC) are specifically differentiated to transport oxygen and carbon dioxide in the blood and they lack most organelles, including mitochondria. The autoxidation of hemoglobin constitutes a major source of reactive oxygen species (ROS). Nitric oxide, which is produced by endothelial nitric oxide synthase (NOS3) or via the hemoglobin-mediated conversion of nitrite, interacts with ROS and results in the production of reactive nitrogen oxide species. Herein we present an overview of anemic diseases that are closely related to oxidative damage. Because the compensation of proteins by means of gene expression does not proceed in enucleated cells, antioxidative and redox systems play more important roles in maintaining the homeostasis of RBC against oxidative insult compared to ordinary cells. Defects in hemoglobin and enzymes that are involved in energy production and redox reactions largely trigger oxidative damage to RBC. The results of studies using genetically modified mice suggest that antioxidative enzymes, notably superoxide dismutase 1 and peroxiredoxin 2, play essential roles in coping with oxidative damage in erythroid cells, and their absence limits erythropoiesis, the life-span of RBC and consequently results in the development of anemia. The degeneration of the machinery involved in the proteolytic removal of damaged proteins appears to be associated with hemolytic events. The ubiquitin-proteasome system is the dominant machinery, not only for the proteolytic removal of damaged proteins in erythroid cells but also for the development of erythropoiesis. Hence, despite the fact that it is less abundant in RBC compared to ordinary cells, the aberrant ubiquitin-proteasome system may be associated with the development of anemic diseases via the accumulation of damaged proteins, as typified in sickle cell disease, and impaired erythropoiesis.

Novel pathogenic variant c.2714C>A (p. Thr905Lys) in the HK1 gene causing severe haemolytic anaemia with developmental delay in an Indian family

Hexokinase (EC 2.7.1.1, Adenosine Tri Phosphate (ATP): D-hexose-6-phosphotransferase) is a crucial regulatory enzyme of the glycolytic pathway (Embden-Meyerhof pathway). Hexokinase deficiency is associated with chronic non-spherocytic haemolytic anaemia (HA) with some exceptional cases showing psychomotor/mental retardation and fetus death. The proband is a four-and-half-year-old female child born of a four-degree consanguineous marriage hailing from South India with autosomal recessive congenital HA associated with developmental delay. She was well till 3 months of her age post an episode of diarrhoea when she was noted to be severely anaemic and requiring regular transfusions. The common causes of HA, haemoglobinopathies, red cell membranopathies and common red cell enzymopathies (G6PD, GPI, PK and P5N) were ruled out. Targeted analysis of whole exome sequencing (WES) using an insilico gene panel for hereditary anaemia was performed to identify pathogenic variants in the patient. Next-generation sequencing revealed a novel homozygous variant in hexokinase gene c.2714C>A (p. Thr905Lys) in exon-18. The pathogenic nature of the variant p. Thr905Lys in the HK1 gene was confirmed collectively by biochemical and molecular studies. Insilico analysis (PolyPhen-2, Provean, Mutation Taster) predicted the variant to be severe disease causing. Multiple sequence alignment demonstrated the conservation of p. Thr905 across the species. The impact of the mutation on the protein structure was studied by PyMOL and Swiss Protein databank viewer.

Prevalence and spectrum of mutations causing G6PD deficiency in Indian populations

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is one of the most common human erythroenzymopathy affecting around 10% of the world population. India is endemic for malaria and antimalarial drugs are known to induce haemolysis in G6PD deficient individuals. Here we report the prevalence as well as the molecular diversity of G6PD deficiency in geographical regions of India.

METHODS AND RESULTS

A total of 20,896 individuals (11,838 males and 9058 females) were screened by DPIP dye decolorisation method followed by quantitation of G6PD enzyme activity on the suspected samples. Molecular analysis was undertaken in a total of 350 G6PD deficient individuals by PCR-RFLP and DNA sequencing. A structural characteristic of the novel variant was deduced by using DynaMut web-server. The prevalence rate of G6PD deficiency varied between 0.8 and 6.3% with an overall prevalence of 1.9%. A total of twelve mutations were identified. Of the total deleterious alleles detected G6PD Orissa (56.5%) was found to be the most predominant variant followed by G6PD Mediterranean (23.6%). G6PD Mediterranean, G6PD Kaiping and G6PD Mahidol were found to be severely deficient variant and 14.1% of them showed undetectable activity. A novel mutation c.544C➔G (R182G) in exon 6 was identified in one tribal male where substitution of arginine by glycine, likely causes the alteration in the alpha helix leading to disruption of secondary structure of the protein.

CONCLUSION

There are large differences in the distribution of G6PD causal variants between Indian states, and this may have implications for the treatment in the malaria endemic areas.

Mutation update: Variants of the CYB5R3 gene in recessive congenital methemoglobinemia

NADH-cytochrome b5 reductase 3 deficiency is an important genetic cause of recessive congenital methemoglobinemia (RCM) and occurs worldwide in autosomal recessive inheritance. In this Mutation Update, we provide a comprehensive review of all the pathogenic mutations and their molecular pathology in RCM along with the molecular basis of RCM in 21 new patients from the Indian population, including four novel variants: c.103A>C (p.Thr35Pro), c.190C>G (p.Leu64Val), c.310G>T (p.Gly104Cys), and c.352C>T (p.His118Tyr). In this update, over 78 different variants have been described for RCM globally. Molecular modeling of all the variants reported in CYB5R3 justifies association with the varying severity of the disease. The majority of the mutations associated with the severe form with a neurological disorder (RCM Type 2) were associated with the FAD-binding domain of the protein while the rest were located in another domain of the protein (RCM Type 1).

Applications of imaging flow cytometry in the diagnostic assessment of red cell membrane disorders

BACKGROUND

Red cell membranopathies refers to phenotypically and morphologically heterogeneous disorders. High throughput imaging flow cytometry (IFC) combines the speed, sensitivity, and phenotyping abilities of flow cytometry with the detailed imagery and functional insights of microscopy to produce high content image analysis with quantitative analysis. We have evaluated the applications of IFC to examine both the morphology as well as fluorescence signal intensity in red cell membranopathies.

METHODS

Fluorescence intensity of eosin-5-maleimide (EMA) labeled red cells was measured for diagnosis of RBC membrane protein defect on Amnis ImageStreamX followed by Image analysis on IDEAS software to study features such as circularity and shape ratio.

RESULTS

The hereditary spherocytosis (HS) group showed significantly decreased MFI (52,800 ± 9,100) than normal controls (81,100 ± 4,700) (p < .05) whereas non-HS showed 78,300 ± 9,900. The shape ratio of hereditary elliptocytosis (HE) was significantly higher (43.8%) than normal controls (14.6%). The circularity score is higher in HS (64.15%) than the normal controls (44.3%) whereas the circularity score was very less in HE (10%) due to the presence of elliptocytes.

CONCLUSIONS

The advantages of the IFC over standard flow cytometry is its ability to provide high-content image analysis and measurement of parameters such as circularity and shape ratio allow discriminating red cell membranopathies (HS and HE) due to variations in shape and size. It could be a single, effective, and rapid IFC test for detection and differentiation of red cell membrane disorders in hematology laboratories where an IFC is available.

Glucose Phosphate Isomerase Deficiency: High Prevalence of p.Arg347His Mutation in Indian Population Associated with Severe Hereditary Non-Spherocytic Hemolytic Anemia Coupled with Neurological Dysfunction

OBJECTIVES

Glucose-6-phosphate isomerase (GPI) deficiency is an autosomal recessive genetic disorder causing hereditary non-spherocytic hemolytic anemia (HNSHA) coupled with a neurological disorder. The aim of this study was to identify GPI genetic defects in a cohort of Indian patients with HNSHA coupled with neurological dysfunction.

METHODS

Thirty-five patients were screened for GPI deficiency in the HNSHA patient group; some were having neurological dysfunction. Enzyme activity was measured by spectrophotometric method. The genetic study was done by single-stranded conformation polymorphism (SSCP) analysis, restriction fragment length polymorphism (RFLP) analysis by the restriction enzyme AciI for p.Arg347His (p.R347H) and confirmation by Sanger's sequencing.

RESULTS

Out of 35 patients, 15 showed 35% to 70% loss of GPI activity, leading to neurological problems with HNSHA. Genetic analysis of PCR products of exon 12 of the GPI gene showed altered mobility on SSCP gel. Sanger's sequencing revealed a homozygous c1040G > A mutation predicting a p.Arg347His replacement which abolishes AciI restriction site. The molecular modeling analysis suggests p.Arg347 is involved in dimerization of the enzyme. Also, this mutation generates a more labile enzyme which alters its three-dimensional structure and function.

CONCLUSIONS

This report describes the high prevalence of p.Arg347His pathogenic variant identified in Indian GPI deficient patients with hemolytic anemia and neuromuscular impairment. It suggests that neuromuscular impairment with hemolytic anemia cases could be investigated for p.Arg347His pathogenic variant causing GPI deficiency because of neuroleukin activity present in the GPI monomer which has neuroleukin action at the same active site and generates neuromuscular problems as well as hemolytic anemia.

Red cell adenylate kinase deficiency in India: identification of two novel missense mutations (c.71A>G and c.413G>A)

Adenylate kinase (AK) deficiency is a rare erythroenzymopathy associated with hereditary nonspherocytic haemolytic anaemia along with mental/psychomotor retardation in few cases. Diagnosis of AK deficiency depends on the decreased level of enzyme activity in red cell and identification of a mutation in the AK1 gene. Until, only eight mutations causing AK deficiency have been reported in the literature. We are reporting two novel missense mutation (c.71A > G and c.413G > A) detected in the AK1 gene by next-generation sequencing (NGS) in a 6-year-old male child from India. Red cell AK enzyme activity was found to be 30% normal. We have screened a total of 32 family members of the patient and showed reduced red cell enzyme activity and confirm mutations by Sanger's sequencing. On the basis of Sanger sequencing, we suggest that the proband has inherited a mutation in AK1 gene exon 4 c.71A > G (p.Gln24Arg) from paternal family and exon 6 c.413G > A (p.Arg138His) from maternal family. Bioinformatics tools, such as SIFT, Polymorphism Phenotyping v.2, Mutation Taster, MutPred, also confirmed the deleterious effect of both the mutations. Molecular modelling suggests that the structural changes induced by p.Gln24Arg and p.Arg138His are pathogenic variants having a direct impact on the structural arrangement of the region close to the active site of the enzyme. In conclusion, NGS will be the best solution for diagnosis of very rare disorders leading to better management of the disease. This is the first report of the red cell AK deficiency from the Indian population.

Molecular diagnosis of unexplained haemolytic anaemia using targeted next-generation sequencing panel revealed (p.Ala337Thr) novel mutation in GPI gene in two Indian patients

Glucose-6-phosphate isomerase (GPI) deficiency is an autosomal recessive genetic disorder causing congenital haemolytic anaemia (CHA). Diagnosis of GPI deficiency by the biochemical method is unpredicted. Molecular diagnosis by identifying genetic mutation is the gold standard method for confirmation of disease, but causative genes involved in CHA are numerous, and identifying a gene-by-gene approach using Sanger sequencing is also cumbersome, expensive and labour intensive. Recently, next-generation targeted sequencing is more useful in the diagnosis of unexplained haemolytic anaemia. We used targeted next-generation sequencing (NGS) clinical panel for diagnosis of unexplained haemolytic anaemia in two Indian patients which were pending for a long time. All possible causes of haemolytic anaemia were found within normal limit. NGS by clinical exome panel revealed homozygous novel missense mutation in exon 12, c.1009G>A (p.Ala337Thr) in both patients. We further confirm by measuring red blood cell GPI activity in the patients and showed deficiency whereas parents were having intermediate activity. c.1009G>A mutation was also confirmed by Sanger sequencing of exon 12 of GPI gene. The structural-functional analysis by bioinformatics software like Swiss PDB, PolyPhen-2 and PyMol suggested that this pathogenic variant has a direct impact on the structural rearrangement at the region near the active site of the enzyme. This rapid and high-performance targeted NGS assay can be configured to detect specific CHA mutations unique to an individual defect, making it a potentially valuable method for diagnosis of unexplained haemolytic anaemia.

Potential involvement of ubiquitin-proteasome system dysfunction associated with oxidative stress in the pathogenesis of sickle cell disease

The ubiquitin-proteasome system (UPS) is an important intracellular proteolytic pathway responsible for the degradation of proteins and oxidative damage; hence it plays a central role in maintaining homeostasis of red blood cells (RBCs). The present study investigated the levels of polyubiquitination, the function of proteasomes and effect of hydroxycarbamide (HC) therapy in RBCs from sickle cell disease (SCD) patients. Polyubiquitinated proteins were found to be elevated in untreated SCD (UT-SCD) patients compared to those in HC-treated SCD patients (HC-SCD) and controls. Activities of β1 and β2 subunits were a little higher in UT-SCD patients, and much higher proteolytic activities were observed in all three subunits (β1, β2 and β5) of RBCs in HC-SCD patients compared to those of UT-SCD patients and controls, although the protein levels of these subunits remained approximately the same. It is notable that, despite HC therapy, some patients showed persistent complications and accumulation of polyubiquitinated proteins. The enhanced proteasomal activity among HC-treated patients might remove the polyubiquitinated protein and could be one of the important mechanisms of therapeutic action. These findings could be useful to understand the pathophysiology of SCD and its clinical heterogeneity and identify a suitable therapeutic target for the better management of these patients.

Novel mutation (R192C) in CYB5R3 gene causing NADH-cytochrome b5 reductase deficiency in eight Indian patients associated with autosomal recessive congenital methemoglobinemia type-I

OBJECTIVE

To investigate the cause of recessive congenital methemoglobinemia (RCM) in Indian families and to identify molecular defect associated with RCM.

METHODS

Eight cases of RCM have been addressed to our laboratory in order to investigate the cause of cyanosis associated with genetic disorders. NADH-cytochrome b5 reductase (cytb5r) enzyme activities were measured by standard methods, and molecular analysis was performed by polymerase chain reaction (PCR) followed by DNA sequencing. The interpretation of mutation effect and the molecular modeling were performed by using specific software DEEP VIEW SWISS-PDB VIEWER and Pymol molecular graphics program.

RESULTS AND DISCUSSION

Eight index cases from four unrelated families were referred for the cause of cyanosis. All patients showed mild to moderate cyanosis without mental retardation or any neurologic abnormalities. The methemoglobin levels were in the range of 11.5-22.41% with 50-70% reduction in CYTB5R activity. Spectroscopic analysis of the hemolysate showed normal peaks suggesting the absence of Hb-M. Molecular characterization showed a novel homozygous mutation p.Arg192Cys in CYB5R3 gene is an evolutionarily conserved position located in exon 7 in all eight index cases. The substitution of Cys is located on the interface of two domains of NADH-binding domain and is close proximity to the adenosine moiety would preclude the reciprocal ionic interaction (salt bridge) between Arg192 and Ile97 and may influence binding of the NADH coenzyme is hypothesized to cause disruption of hydrogen bonding and instability. Our study indicated that novel homozygous mutation p.Arg192Cys in CYB5R3 gene present in eight cases and the possibility of high prevalence of heterozygous in Indian population causing Type I RCM.

A microplate reader-based method to quantify NADH-cytochrome b5 reductase activity for diagnosis of recessive congenital methaemoglobinemia

OBJECTIVES

Congenital methemoglobinemia due to NADH-cytochrome b5 reductase 3 (CYB5R3) deficiencies is an autosomal recessive disorder that occurs sporadically worldwide, A sensitive, accurate, and rapid analysis of NADH-CYB5R enzyme concentrations is necessary for the diagnosis of RCM. Here we present an alternative microplate method that is based on a standard 96-well microplate format and microplate reader that simplify the quantification of NADH-CYB5R activity.

METHODS

TECAN (Infinite 200 PRO series) microplate reader with Tecan's proven Magellan™ software measured the NADH-CYB5R enzyme activity in 250 normal controls and previously diagnosed 25 cases of RCM due to NADH-CYB5R deficiency in the Indian population using 96-well microplates using 200 μl of total reaction mixture and also compared with standard spectrophotometric assay. We have also studied stability of the hemolysate stored at 4 and -20°C temperature.

RESULTS AND DISCUSSION

Enzyme activity in all 25 samples ranged from 6.09 to 10.07 IU/g Hb (mean ± SD: 8.08 ± 1.99 IU/g Hb) where as normal control ranged (n = 250) between 13.42 and 21.58 IU/g Hb) (mean ± SD: 17.5 ± 4.08 IU/g of Hb). Data obtained from the microplate reader were compared with standard spectrophotometer method and found 100% concordance using both methods. Microplate method allows differentiating between normal, deficient and intermediate enzyme activity. It was observed that samples had significant loss of activity when stored at 4°C and retained stable activity at -20°C for 1 week time.

CONCLUSION

Our new method, incorporating a whole process of enzyme assay into a microplate format is readily applicable and allows rapid monitoring of enzyme assay. It is readily applicable to quantitative assay on pediatric sample as well as large number of samples for population screening.

A novel nine base deletion mutation in NADH-cytochrome b5 reductase gene in an Indian family with recessive congenital methemoglobinemia-type-II

Recessive hereditary methemoglobinemia (RCM) associated with severe neurological abnormalities is a very rare disorder caused by NADH- cytochrome b5 reductase (cb5r) deficiency (Type II). We report a case of 11 month old male child who had severe mental retardation, microcephaly and gross global developmental delay with methemoglobin level of 61.1%. The diagnosis of NADH-CYB5R3 deficiency was made by the demonstration of significantly reduced NADH-CYB5R3 activity in the patient and intermediate enzyme activity in both the parents. Mutation analysis of the CYB5R gene revealed a novel nine nucleotide deletion in exon 6 leading to the elimination of 3 amino acid residues (Lys173, Ser174 and Val 175). To confirm that this mutation was not an artifact, we performed PCR-RFLP analysis using the restriction enzyme Drd I. As the normal sequence has a restriction recognition site for Drd I which was eliminated by the deletion, a single band of 603-bp was seen in the presence of the homozygous mutation. Molecular modeling analysis showed a significant effect of these 3 amino acids deletion on the protein structure and stability leading to a severe clinical presentation. A novel homozygous 9 nucleotide deletion (p.K173–p.V175del3) is shown to be segregated with the disease in this family. Knowing the profile of mutations would allow us to offer prenatal diagnosis in families with severe neurological disorders associated with RCM — Type II.

Hemoglobinopathy screening by osmotic fragility test based on flow cytometer or naked eye

BACKGROUND

Diagnosis of hemoglobin (Hb) disorders is based mostly on abnormal red blood cell (RBC) indices, elevated levels of HbA2, HbF, or any other Hb on the Variant high performance liquid chromatography (HPLC) system, and confirmation by molecular methods. However, large scale population screening is of prime importance and requires a simple, accurate, and cost effective technique. We have tried to compare the sensitivity of the widely used Naked Eye Single Tube Red Cell Osmotic Fragility Test (NESTROFT) and the osmotic fragility described as % residual RBCs through flow cytometry for population screening.

METHODS

The count of residual red cells was measured sequentially in real-time using flow cytometry. NESTROFT was performed using a 0.36% buffered saline. HbA2 and HbF levels along with other abnormal Hbs were determined on the Variant HPLC System. Molecular studies were done to confirm the diagnosis.

RESULTS

The normal group showed a significantly lower percentage of residual RBCs (48.08 ± 11.87) as compared to cases (β thalassemia trait-82.97 ± 12.20, α thalassemia trait-72.58 ± 8.34, and HbS trait-85.00 ± 4.05). The sensitivity and specificity of NESTROFT was high for both β thalassemia traits (98.33 and 96.72%, respectively) and α thalassemia traits (100 and 96.72%, respectively) but very low sensitivity for HbS traits (54.84%).

CONCLUSION

Flow cytometric osmotic fragility was a more sensitive method to discriminate normal from the group of hemoglobinopathy carriers as compared to NESTROFT which missed majority of HbS carriers. However, in view of feasibility and cost effectiveness, NESTROFT could still be used for population screening of thalassemia. © 2014 International Clinical Cytometry Society.

Hemoglobinopathy Screening by Osmotic Fragility Test Based on Flow Cytometer or Naked Eye

BACKGROUND

Diagnosis of hemoglobin disorders is based mostly on abnormal red blood cell indices, elevated levels of HbA2, HbF or any other Hb on the Variant HPLC system and confirmation by molecular methods. However, large scale population screening is of prime importance and requires a simple, accurate and cost effective technique. We have tried to compare the sensitivity of the widely used NESTROFT and the osmotic fragility described as percentage residual RBCs through flow cytometry for population screening.

METHODS

The count of residual red cells was measured sequentially in real-time using flow cytometry. NESTROFT was performed using a 0.36% buffered saline. HbA2 and HbF levels along with other abnormal hemoglobins were determined on the Variant HPLC System. Molecular studies were done to confirm the diagnosis.

RESULTS

The normal group showed a significantly lower percentage of residual RBCs (48.08±11.87) as compared to cases (β thalassemia trait- 82.97±12.20, α thalassemia trait-72.58±8.34 and HbS trait- 85.00±4.05). The sensitivity and specificity of NESTROFT was high for both β thalassemia traits (98.33% and 96.72% respectively) and α thalassemia traits (100% and 96.72 % respectively) but very low sensitivity for HbS traits (54.84%).

CONCLUSION

Flow cytometric osmotic fragility was a more sensitive method to discriminate normals from the group of hemoglobinopathy carriers as compared to NESTROFT which missed majority of Hb S carriers. However, in view of feasibility and cost effectiveness, NESTROFT could still be used for population screening of thalassemia. This article is protected by copyright. All rights reserved.

Molecular and clinical heterogeneity in pyruvate kinase deficiency in India

We studied the PK-LR gene in 10 unrelated Indian patients with congenital haemolytic anemia associated with erythrocyte pyruvate kinase deficiency. The patients had a variable presentation ranging from a very mild compensated hemolysis to severe anemia. Nine different mutations were detected among the 20 mutated alleles identified: one deletion (c.1042-1044del) p.Lys348del and eight single-nucleotide (nt) substitutions resulting in amino acid exchanges c.397A>G (p.Asn133Asp), c.992A>G (p.Asp331Gly), c.1072G>A (p.Gly358Arg), c.1076G>A (p.Arg359His), c.1219G>A (p.Glu407Lys), c.1241C>T (p.Pro414Leu), c.1436G>A (p.Arg479His) and c.1529G>A (p.Arg510Gln) were identified. Although all the exons, the flanking regions and the promoter region were sequenced in all cases, we failed to detect the second expected mutation in two subjects. Two mutations [c.397A>G; c.1241C>T] were novel. These novel missense mutations involved highly conserved amino acids. Two mutations were identified for the first time in the homozygous state globally (c1042-1044del; c.1072G>A) and two other mutations were identified for the first time in our population (c.1076G>A; c.1529G>A). This study along with our earlier report suggests that the most frequent mutations in India would appear to be c.1436G>A (18.33%), followed by c.992A>G (11.66%) and c.1456C>T (11.66%). Structural implications of amino acid substitutions were correlated with the clinical phenotypes seen.

A new simple approach for the determination of pyrimidine 5'-nucleotidase activity in human erythrocytes using an ELISA reader

INTRODUCTION

Pyrimidine 5' nucleotidase type I (P5'N-1) deficiency is the most frequent abnormality of cell nucleotide metabolism causing hereditary non spherocytic hemolytic anemia (HNSHA). The aim of this study was to develop a simple method of determination of P5'N-1 activity in human erythrocytes using an ELISA reader

METHODS

Determination of P5'N-1 activity is based on the liberation of inorganic phosphorus (Pi) after incubation with uridine monophosphate/cytidine monophosphate. Inorganic phosphorus (Pi), a product of the enzymatic reaction is directly quantitated from its ultraviolet absorbance. Purine/Pyrimidine nucleotides ratio (OD 260: OD 280) was also measured

RESULTS

P5'N-1 deficient patients showed reduction in P5'N-1 activity (Mean ± SD; 4.06 ± 0.66 using an ELISA reader & 6.25 ± 1.37 using a spectrophotometer) as compared to the normal control group (ELISA reader: 13.24 ± 3.42 & Spectrophotometer: 18.25 ± 3.20). Heterozygotes showed intermediate activity (ELISA reader: 6.06 ± 0.48 & Spectrophotometer: 8.06 ± 1.28), however they would have been missed on screening using the Purine/Pyrimidine nucleotides ratio

CONCLUSION

Determination of P5'N-1 activity by using an ELISA reader is a new, simple, less time consuming and reliable method. It also avoids the use of radioactive material or HPLC which is a significant advantage.

Flow cytometric osmotic fragility--an effective screening approach for red cell membranopathies

BACKGROUND

Among the red cell membrane disorders, hereditary spherocytosis (HS) is one of the most common causes of inherited hemolytic anemia. The aim of this study was to compare the flow-cytometric approach for screening of red cell membrane disorders based on osmotic fragility with the eosin-5-maleimide (E5'M) dye test. A group of β-thalassemia heterozygotes were also studied.

METHODS

A red cell suspension was spiked with deionized water during acquisition and the count of residual red cells measured sequentially in real-time using flow cytometry. Fluorescence intensity of red cells stained with eosin-5-maleimide was also measured.

RESULTS

The hereditary spherocytosis (HS) group showed significantly decreased percentage residual red cells (9.31% ± 3.75%) (P = 0.0091) whereas the β-thalassemia group showed a significant increase (93.56% ± 12.98%) (P = 0.0008) compared to the normal control group (46.26% ± 11.33%). The cut off value of the flow cytometric osmotic fragility (FCM OF) test for red cell membrane disorders was 23.59% giving a sensitivity of 100% and specificity of 98%.

CONCLUSIONS

The advantages of the FCM OF test are that it is quantitative, time effective and requires only deionized water for the measurement of osmotic fragility. It could be an effective first line screening approach for red cell membrane disorders in hematology laboratories where a flow cytometer is available.

Hemolytic anemia and distal renal tubular acidosis in two Indian patients homozygous for SLC4A1/AE1 mutation A858D

Familial distal renal tubular acidosis (dRTA) can be caused by mutations in the Cl2/HCO32 exchanger of the renal Type A intercalated cell, kidney AE1/SLC4A1. dRTA-associated AE1 mutations have been reported in families from North America, Europe, Thailand, Malaysia, Papua-New Guinea, Taiwan, and the Philippines, but not India. The dRTA mutation AE1 A858D has been detected only in the context of compound heterozygosity. We report here two unrelated Indian patients with combined hemolytic anemia and dRTA who share homozygous A858D mutations of the AE1/SLC4A1 gene. The mutation creates a novel restriction site that is validated for diagnostic screening.

Molecular diversity of hemoglobin H disease in India

This study was undertaken to evaluate the variable clinical expression of hemoglobin (Hb) H disease in India. For the study, alpha genotyping was done in 8 patients with Hb H disease using multiplex polymerase chain reaction and DNA sequencing. The study revealed that 4 genotypes (- -(SEA)/ -alpha(3.7), - -(SA)/-alpha(3.7), - -(SEA)/-alpha(3.7 Sallanches), - -alpha(3.7)/-alpha(3.7 Sallanches)) were responsible for Hb H disease, the alpha+ thalassemia mutation (-alpha(3.7) deletion) being the most common defect. The nondeletional mutation Hb Sallanches (alpha 2 codon 104 G --> A) was seen in 3 cases. Two unique and novel genotypes leading to Hb H disease were characterized (- -(SEA)/-alpha(3.7 Sallanches) and -alpha(3.7)/-alpha(3.7 Sallanches)). Because a majority of patients with Hb H disease do not have severe manifestations, prenatal diagnosis is usually unwarranted in India.

Five alpha globin chain variants identified during screening for haemoglobinopathies

BACKGROUND

This study was undertaken to analyse cases of microcytosis, and/or haemolytic anaemia where an unusual peak on HPLC or an abnormal electrophoretic mobility in isolation or along with common beta-globin gene defects was found, and to identify the molecular abnormality in them.

PATIENTS AND METHODS

Investigations included a complete blood count, HPLC analysis, cellulose acetate electrophoresis (pH 8.9), heat stability test and DNA sequencing.

RESULTS

Five alpha chain variants were identified. This is the first report of Hb Jackson and Hb O Indonesia in the Indian population. The presence of Hb J Meerut along with Hb E and Hb J Paris I with heterozygous beta-thalassaemia are uncommon associations. Hb Sun Prairie would have remained undetected in the heterozygous state. The presence of a homozygous child in the family helped to identify this variant.

CONCLUSIONS

This study emphasizes the need to undertake systematic investigations while screening for the beta haemoglobinopathies to identify rare alpha chain variants in a population.

Spectrum of novel mutations in the human PKLR gene in pyruvate kinase-deficient Indian patients with heterogeneous clinical phenotypes

Eighteen unrelated pyruvate kinase (PK)-deficient Indian patients were identified in the past 4 years with varied clinical phenotypes ranging from a mild chronic haemolytic anaemia to a severe transfusion-dependent disorder. We identified 17 different mutations in the PKLR gene among the 36 mutated alleles. Ten novel mutations were identified: 427G>A, 499C>A, 1072G>A, 1180G>T, 1216G>A, 1220A>G, 644delG, IVS5 (+20) C>A, IVS9 (+44) C>T, and IVS9 (+93) A>C. A severe syndrome was commonly associated with some mutations, 992A>G, 1436G>A, 1220A>G, 644delG and IVS9 (+93) A>C, in the PKLR gene. Molecular graphics analysis of human red blood cell PK (RPK), based on the crystal structure of human PK, shows that mutations located near the substrate or fructose 1,6-diphosphate binding site may change the conformation of the active site, resulting in very low PK activity and severe clinical symptoms. The mutations target distinct regions of RPK structure, including domain interfaces and catalytic and allosteric sites. In particular, the 1216G>A and 1219G>A mutations significantly affect the interdomain interaction because they are located near the catalytic site in the A/B interface domains. The most frequent mutations in the Indian population appear to be 1436G>A (19.44%), followed by 1456C>T (16.66%) and 992A>G (16.66%). This is the first study to correlate the clinical profile with the molecular defects causing PK deficiency from India where 10 novel mutations that produce non-spherocytic haemolytic anaemia were identified.

Prenatal diagnosis for a novel homozygous mutation inPKLR gene in an Indian family

OBJECTIVE

To provide prenatal diagnosis of pyruvate kinase deficiency by direct DNA analysis in an Indian family.

MATERIALS AND METHOD

This case report describes diagnosis of a novel homozygous mutation in PKLR gene that subsequently helped the family in the next pregnancy.

RESULTS

Advancement in molecular genetics has resulted in the prenatal diagnosis of relatively uncommon genetic disorders like pyruvate kinase deficiency.

CONCLUSION

This case reiterates the importance of application of molecular genetics in clinical practice and prenatal diagnosis especially for rare, incurable genetic disorders.

Red cell pyruvate kinase deficiency in neonatal jaundice cases in India

OBJECTIVE

Pyruvate Kinase (PK) deficiency is the most common enzymopathy of the glycolytic pathway in erythrocytes. It constitutes one of the common causes of hereditary non-spherocytic hemolytic anemia. The aim of this study was to screen newborns in India for pyruvate kinase (PK) deficiency in relation to unconjugated hyperbilirubinemia.

METHODS

Laboratory investigations done included complete blood counts, reticulocyte counts, direct and indirect bilirubin, assay of G6PD and PK activity, ATP and 2,3 DPG levels. All variables were studied in 50-cord blood samples from normal deliveries and 218 neonates with hyperbilirubinemia.

RESULTS

7 of the 218 cases of neonatal jaundice were PK deficient with 30-40% reduction in PK activity. These cases also had a 3-4-fold increase in 2,3 DPG:ATP ratios, which is one of the additional indicators for PK deficiency. Six of the 7 infants had a severe clinical course.

CONCLUSION

This study shows that the prevalence of PK deficiency in Indian neonatal jaundice cases is 3.21%, which is relatively high. This emphasizes the need for screening neonatal hyperbilirubinemia cases in India for PK deficiency.