Mechanosensitive Piezo1 ion channel protein (PIEZO1 gene): update and extended mutation analysis of hereditary xerocytosis in India.

Hereditary xerocytosis (HX), also known as dehydrated stomatocytosis (DHSt) is a dominantly inherited genetic disorder exhibiting red cell membrane dehydration caused by the loss of the monovalent cation K+ and water. Variants in mechanosensitive Piezo ionic channels of the PIEZO1 gene are the primary cause of HX. We have utilized high throughput and highly precise next-generation sequencing (NGS) to make a diagnosis and examine the genotype-phenotype relationship in inflexible HX cases. Seven unrelated patients with unexplained hemolytic anemia were scrutinized with a panel probing 8000 genes related to congenital anemia. Targeted next-generation sequencing identified 8 missense variants in the PIEZO1 gene in 7 unrelated Indian patients. Three of the 8 variants are novel (c.1795G > C, c.2915G > A, c.7372 T > C) and the remaining five (c.4082A > G, c.6829C > A, c.7374C > G, c.7381G > A, c.7483_7488dup) are previously reported. The variants have been validated by Sanger sequencing. One patient with autosomal dominant mutation (c.7372 T > C) is associated with iron refractory iron deficiency anemia. Of the 7 patients, one has HX in combination with a novel homozygous variant (c.994G > A) in the PKLR gene causing PK deficiency resulting in severe clinical manifestations with phenotypic variability. In silico prediction using bioinformatics tools were used to study the possible damaging effects of the novel variants. Structural-functional analysis of the novel variants was investigated by molecular modeling software (PyMOL and Swiss PDB). These results encompass the heterogeneous behavior of mechano-sensitive Piezo1 protein observed in HX patients in India. Moreover, NGS imparted a subtle, economical, and quick tool for understanding the genetic cause of undiagnosed cases of congenital hemolytic anemia. NGS grants a potential technology integrating clinical history together with molecular report profiting in such patients and their families.

Development of High-Resolution Melting Curve Analysis for rapid detection of SEC23B gene mutation causing Congenital Dyserythropoietic Anemia type II in Indian population.

BACKGROUND: Congenital dyserythropoietic anemias (CDAs) are a very rare and heterogeneous group of disorders characterized by ineffective erythropoiesis. CDA II is caused by mutations in the SEC23B gene. The most common mutation reported in India is c.1385 A > G, p.Y462C. There is no simple and cost-effective confirmatory diagnostic test available for CDA, and therefore, many patients remain undiagnosed. High-resolution melting curve (HRM) analysis is a polymerase chain reaction (PCR) based technique applied to identify genetic differences and scan nucleic acid sequences. HRM can be used to rapidly screen the common mutation causing CDA II in the Indian population. Thus, we studied the use of High-Resolution Melting Curve Analysis to detect common mutation causing CDA II in the Indian population. METHOD: 11 patients having SEC23B (Y462C) mutation causing CDA II are considered for this study. HRM was used to check the presence of Y462C mutation. To verify the accuracy of the HRM analysis, we compared HRM results with the results of Sanger sequencing. This helped us to confirm the diagnosis. RESULTS: We have described the clinical, hematological, and genetic data of eleven patients suffering from CDAII. According to HRM and Sanger sequencing, a homozygous SEC23B (Y462C) mutation was present in all patients, whereas a heterozygous Y462C mutation was present in their parents. CONCLUSION: Our data showed that High-Resolution Melting (HRM) analysis could be used to rapidly screen common SEC23B mutation that causes CDA II in the Indian population.

Functional characterization and modified rescue of novel AE1 mutation R730C associated with overhydrated cation leak stomatocytosis.

We report the novel, heterozygous AE1 mutation R730C associated with dominant, overhydrated, cation leak stomatocytosis and well-compensated anemia. Parallel elevations of red blood cell cation leak and ouabain-sensitive Na(+) efflux (pump activity) were apparently unaccompanied by increased erythroid cation channel-like activity, and defined ouabain-insensitive Na(+) efflux pathways of nystatin-treated cells were reduced. Epitope-tagged AE1 R730C at the Xenopus laevis oocyte surface exhibited severely reduced Cl(-) transport insensitive to rescue by glycophorin A (GPA) coexpression or by methanethiosulfonate (MTS) treatment. AE1 mutant R730K preserved Cl(-) transport activity, but R730 substitution with I, E, or H inactivated Cl(-) transport. AE1 R730C expression substantially increased endogenous oocyte Na(+)-K(+)-ATPase-mediated (86)Rb(+) influx, but ouabain-insensitive flux was minimally increased and GPA-insensitive. The reduced AE1 R730C-mediated sulfate influx did not exhibit the wild-type pattern of stimulation by acidic extracellular pH (pH(o)) and, unexpectedly, was partially rescued by exposure to sodium 2-sulfonatoethyl methanethiosulfonate (MTSES) but not to 2-aminoethyl methanethiosulfonate hydrobromide (MTSEA) or 2-(trimethylammonium)ethyl methanethiosulfonate bromide (MTSET). AE1 R730E correspondingly exhibited acid pH(o)-stimulated sulfate uptake at rates exceeding those of wild-type AE1 and AE1 R730K, whereas mutants R730I and R730H were inactive and pH(o) insensitive. MTSES-treated oocytes expressing AE1 R730C and untreated oocytes expressing AE1 R730E also exhibited unprecedented stimulation of Cl(-) influx by acid pH(o). Thus recombinant cation-leak stomatocytosis mutant AE1 R730C exhibits severely reduced anion transport unaccompanied by increased Rb(+) and Li(+) influxes. Selective rescue of acid pH(o)-stimulated sulfate uptake and conferral of acid pH(o)-stimulated Cl(-) influx, by AE1 R730E and MTSES-treated R730C, define residue R730 as critical to selectivity and regulation of anion transport by AE1.

Genotypic analysis of SLC4A1 A858D mutation in Indian population associated with distal renal tubular Acidosis (dRTA) coupled with hemolytic anemia.

INTRODUCTION: Although distinctive, distal renal tubular acidosis (dRTA) and Hereditary Spherocytosis (HS) shares a common protein, the anion exchanger1 (AE1) encoded by SLC4A1gene. In spite of this, the co-existence of dRTA and HS has rarely been observed. To date, 23 mutations have been identified in SLC4A1 gene causing both autosomal recessive (AR) and autosomal dominant (AD) forms of dRTA. METHODS: We have assessed the applicability of the High Resolution Melting curve (HRM) method for the detection of SLC4A1 (A858D) mutation in 12 Indian families having AR dRTA coupled with HS. The reliability of the HRM analysis was verified by comparing the results of the HRM method with those of conventional methods such as Polymerase Chain Reaction-Restriction Fragment-Length Polymorphism (PCR-RFLP) and Sanger sequencing thereby confirming the diagnosis. RESULTS: We here described the clinical, hematological and genetic data of 16 individuals from 12 families having AR dRTA coupled with HS. All patients carried homozygous SLC4A1 (A858D) mutation, whereas their family members had heterozygous A858D obtained by HRM analysis and confirmed by RFLP and Sanger sequencing. CONCLUSION: Our data indicates that a missense mutation of A858D in SLC4A1 gene is the most common cause of dRTA coupled with HS in the Indian population. HRM analysis can be used as a rapid screening method for common SLC4A1 mutations that cause AR dRTA in the Indian population.

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.

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 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.

Study of pathophysiology and molecular characterization of congenital anemia in India using targeted next-generation sequencing approach.

Most patients with anemia are diagnosed through clinical phenotype and basic laboratory testing. Nonetheless, in cases of rare congenital anemias, some patients remain undiagnosed despite undergoing an exhaustive workup. Genetic testing is complicated by the large number of genes that are involved in rare anemias, due to similarities in the clinical presentation. We sought to enhance the diagnosis of patients with congenital anemias by using targeted next-generation sequencing. The genetic diagnosis was performed by gene capture followed by next-generation sequencing of 76 genes known to cause anemia syndromes. Genetic diagnosis was achieved in 17 of 21 transfusion-dependent patients and undiagnosed by conventional workup. Four cases were diagnosed with red cell membrane protein defects, four patients were diagnosed with pyruvate kinase deficiency, one case of adenylate kinase deficiency, one case of glucose phosphate isomerase deficiency, one case of hereditary xerocytosis, three cases having combined membrane and enzyme defect, two cases with Diamond-Blackfan anemia (DBA) and 1 with CDA type II with 26 different mutations, of which 21 are novel. Earlier incorporation of this NGS method into the workup of patients with congenital anemia may improve patient care and enable genetic counselling.

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.

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.

A novel G143D mutation in the NADH-cytochrome b5 reductase gene in an Indian patient with type I recessive hereditary methemoglobinemia.

We report a novel homozygous mutation responsible for NADH-b(5)R deficiency in a family from Ratnagiri district in western India with recessive congenital methemoglobinemia (RCM) type I. The propositus was a 20-year-old female with a history of increasing cyanosis exacerbated by fever and weakness. There was no history of cardiac illness or exposure to drugs and chemicals. The methemoglobin level was 38.0% in the propositus with 70% reduction in NADH-b(5)R activity. Spectroscopic analysis of the hemolysate showed normal peaks suggesting absence of Hb-M. There was no hemoglobin instability and G6PD activity was normal. This novel G-->A homozygous mutation at codon 143 in exon 5 was identified by SSCP followed by DNA sequencing and results in a glycine to aspartic acid substitution in the cytochrome b(5) reductase protein. This mutation, which is located outside the FAD and NADH binding domain, leads to mild cyanosis. Investigations of the family members revealed that both the parents and a brother of the propositus were heterozygous for the G143D mutation.

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.

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.

Congenital methemoglobinemia caused by Hb-MRatnagiri (beta-63CAT-->TAT, His-->Tyr) in an Indian family.

Hb-M is a very rare hemoglobinopathy in the Indian subcontinent. We report a family with Hb-M with lifelong cyanosis from the Ratnagiri district in western India. The propositus was a 11-year-old female child with a history of increasing cyanosis exacerbated by fever and weakness. Similar complaints were also noted in her mother and five maternal family members. There was no history of cardiac illness or exposure to drugs and chemicals. The methemoglobin level was 39.3% in the propositus and 21.1% in her mother with normal NADH-methemoglobin reductase activity. Abnormal absorption peaks by spectroscopic analysis, presence of hemoglobin instability, and a slow-moving band on starch gel electrophoresis supported the presence of Hb-M. Automated DNA sequence analysis of the beta globin gene showed a C-->T substitution at codon 63. This leads to a substitution of histidine (CAT) by tyrosine (TAT) at the beta 63 (E7) position, similar to Hb-M Saskatoon. We have named this variant as Hb-M(Ratnagiri).

Congenital methemoglobinemia due to NADH-methemoglobin reductase deficiency in three Indian families.

Congenital methemoglobinemia is a relatively rare clinical disorder characterized by life-long cyanosis, caused by either an inherited mutant hemoglobin (Hb-M) or deficiency of physiologically active NADH-dependent methemoglobin reductase (NADH-MR). NADH-MR deficiency leads to two different types of recessive congenital methemoglobinemia. In type I, cyanosis is the only major symptom and NADH-MR deficiency is restricted only to the red blood cells. In type II, cyanosis is associated with severe mental retardation and neurological impairment. The objective of this study is to establish the cause of cyanosis in our cases of congenital methaemoglobinemia. Erythrocyte NADH-MR activity was assayed spectrophotometrically. Spectral analysis of the hemolysate treated with potassium ferricyanide was recorded between 400-700 nm and Hb electrophoresis on starch gel at pH 7.0 was done to rule out the presence of Hb-M. NADH-MR deficiency was detected in 3 families. There was a history of consanguinity in one of these cases. The three propositi presented with breathlessness, fever and peripheral cyanosis. There was no history of cardiac illness or exposure to drugs and chemicals. There were no signs and symptoms of mental retardation. The presence of Hb-M was ruled out. Hb-A2, Hb-F, G6PD activity and reduced glutathione levels were normal. NADH-MR activity in all the cases ranged from 4.1 to 9.2 IU/g Hb (normal range 7.0-24.0 IU/g Hb). We describe NADH-MR deficiency in three unrelated cases (age 4 months to 6 years) where the activity of the enzyme was 30-40% of normal. These three cases of congenital methemoglobinemia are due to type-I NADH-MR deficiency without mental retardation.