Hereditary Red Cell Membrane Disorders in Japan: Their Genotypic and Phenotypic Features in 1014 Cases Studied

One-step amplification refractory mutation system-PCR/high-resolution melting curve assay for carrier detection of red blood cell membranopathy caused by common SPTB mutations

INTRODUCTION

Hereditary pyropoikilocytosis (HPP) is the most common cause of non-thalassemic severe inherited hemolytic anemia in Thai population. Up to 90% of affected patients harbor biallelic mutations of SPTB Providence (SPTB c.6055T>C), SPTB Buffalo (SPTB c.6074T>G), and SPTB Chiang Mai (SPTB c.6224A>G). This study aimed to develop a simple assay for mass screening of the three common SPTB mutations and to study their carrier frequencies in a healthy Thai population.

METHODS

We combined multiplex amplification refractory mutation system-PCR (ARMS-PCR) and high-resolution melting (HRM) curve analysis to create a one-step single-tube assay. The primers were designed to generate products with different melting temperatures in the presence of 6055C, 6074G, and 6224G. Internal control primers were added for quality control. Residual samples from blood donors and healthy adolescents were collected and tested for the three common SPTB mutations using the newly developed assay.

RESULTS

Optimized multiplex ARMS-PCR/HRM curve assay yielded well-separated melt curves to detect the three SPTB mutations with 4-h turnaround time. The assay was validated in screening of 2261 non-repetitive blood donors and 89 adolescents, in which 10 (0.43%), 2 (0.09%), and 3 (0.13%) individuals were identified as carriers of SPTB Providence, SPTB Buffalo, and SPTB Chiang Mai, respectively. All mutated SPTB and 20 random wild-type samples were confirmed using Sanger sequencing with 100% accuracy.

CONCLUSION

The novel ARMS-PCR/HRM curve assay is simple, accurate, and time-effective for mass screening of the common SPTB mutations. This can be employed to prevent HPP birth in a Thai population.

Molecular characteristics of hereditary red blood cell membrane disorders in Thailand: a multi-center registry

Red blood cell (RBC) membrane disorders represent a significant category of hereditary hemolytic anemia; however, information from Southeast Asia is limited. We established a national registry aiming to characterize RBC membrane disorders and their molecular features in Thailand. A total of 100 patients (99 kindreds) diagnosed with RBC membrane disorders between 2011 and 2020 from seven university hospitals were enrolled. The most prevalent disorders observed were hereditary elliptocytosis (HE; n=33), hereditary pyropoikilocytosis (HPP; n=28), hereditary spherocytosis (HS; n=19), Southeast Asian ovalocytosis (SAO; n=10 of 9 kindreds), and two cases of homozygous SAO. The remaining cases were grouped as unclassified membrane disorder. Seventy-six patients (76%) were molecularly confirmed by PCR, direct DNA sequencing, or hi-throughput sequencing. The primary causative gene for HE and HPP was SPTB, accounting for 28 out of 29 studied alleles for HE and 56 of 56 studied alleles for HPP. In the case of HS, dominant sporadic mutations in the ANK1 gene (n=4) and SPTB gene (n=3) were identified as the underlying cause. Notably, the four most common variants causing HE and HPP were SPTB Providence (c.6055 T>C), SPTB Buffalo (c.6074 T>G), SPTB Chiang Mai (c.6224 A>G), and SPTB c.6171__82delins TGCCCAGCT. These recurrent SPTB mutations accounted for 79 out of 84 mutated SPTB alleles (94%). In summary, HE and hereditary HPP associated with recurrent SPTB mutations are the predominant types of RBC membrane disorders observed in Thailand. These findings have significant implications for the clinical management and future research of RBC membrane disorders in the region.

Diagnostic yield of targeted next-generation sequencing for pediatric hereditary hemolytic anemia

BACKGROUND

Hereditary hemolytic anemia (HHA) refers to a heterogeneous group of genetic disorders that share one common feature: destruction of circulating red blood cells (RBCs). The destruction of RBCs may be due to membranopathies, enzymopathies, or hemoglobinopathies. Because these are genetic disorders, incorporation of next-generation sequencing (NGS) has facilitated the diagnostic process of HHA.

METHOD

Genetic data from 29 patients with suspected hereditary anemia in a tertiary hospital were retrospectively reviewed to evaluate the efficacy of NGS on hereditary anemia diagnosis. Targeted NGS was performed with custom probes for 497 genes associated with hematologic disorders. After genomic DNA was extracted from peripheral blood, prepared libraries were hybridized with capture probes and sequenced using NextSeq 550Dx (Illumina, San Diego, CA, USA).

RESULT

Among the 29 patients, ANK1 variants were detected in five, four of which were pathogenic or likely pathogenic variants. SPTB variants were detected in six patients, five of which were classified as pathogenic or likely pathogenic variants. We detected g6pd pathogenic and spta1 likely pathogenic variants in two patients and one patient, respectively. Whole-gene deletions in both HBA1 and HBA2 were detected in two patients, while only HBA2 deletion was detected in one patient. One likely pathogenic variant in PLKR was detected in one patient, and one likely pathogenic variant in ALAS2 was detected in another.

CONCLUSION

Here, NGS played a critical role in definitive diagnosis in 18 out of 29 patients (62.07%) with suspected HHA. Thus, its incorporation into the diagnostic workflow is crucial.

Novel Variant of the SLC4A1 Gene Associated with Hereditary Spherocytosis

Hereditary spherocytosis (HS) refers to the group of the most frequently occurring non-immune hereditary hemolytic anemia in people of Caucasian central or northern European ancestry. HS is mainly associated with pathogenic variants of genes encoding defects in five membrane proteins, including anion exchanger 1 encoded by the SLC4A1 gene. In this study, in a family affected with HS, we identified a hitherto unreported AE1 defect, variant p.G720W. The result of it is most likely the HS phenotype. Molecular dynamics simulation study of the AE1 transmembrane domain may indicate reasonable changes in AE1 domain structure, i.e., significant displacement of the tryptophan residue towards the membrane surface connected with possible changes in AE1 function. The WES analysis verified by classical sequencing in conjunction with biochemical analysis and molecular simulation studies shed light on the molecular mechanism underlying this case of hereditary spherocytosis, for which the newly discovered AE1 variant p.G720W seems crucial.

Clinical and genetic diagnosis of thirteen Japanese patients with hereditary spherocytosis

Hereditary spherocytosis is the most frequent cause of hereditary hemolytic anemia and is classified into five subtypes (SPH1-5) according to OMIM. Because the clinical and laboratory features of patients with SPH1-5 are variable, it is difficult to classify these patients into the five subtypes based only on these features. We performed target capture sequencing in 51 patients with hemolytic anemia associated with/without morphological abnormalities in red blood cells. Thirteen variants were identified in five hereditary spherocytosis-related genes (six in ANK1 [SPH1]; four in SPTB [SPH2]; and one in each of SPTA1 [SPH3], SLC4A1 [SPH4], and EPB42 [SPH5]). Among these variants, seven were novel. The distribution pattern of the variants was different from that reported previously in Japan but similar to those reported in other Asian countries. Comprehensive genomic analysis would be useful and recommended, especially for patients without a detailed family history and those receiving frequent blood transfusions due to chronic hemolytic anemia.

Efficacy of cytochemical tests in gene analysis of hereditary spherocytosis: a case study of six patients with different disease subtypes

OBJECTIVES

In this study, clinical and biochemical methods were utilized to predict the final diagnosis of hereditary spherocytosis (HS), correlate the diagnosis with splenectomy, and examine the usefulness of this approach.

METHODS

We biochemically and cytochemically analysed erythrocyte membrane proteins before making a final HS diagnosis based on gene analysis to compare diagnostic approaches. The clinical features of six patients with various subtypes of HS and symptoms were observed by blood analysis using eosin-5'-maleimide staining, biochemical analysis using sodium dodecyl sulphate - polyacrylamide gel electrophoresis with western blotting, and mass spectrometry. Finally, diagnostic membrane gene analysis was performed.

RESULTS

Five of the six patients showed mild to moderate or severe anaemia, and the other patient was non-anaemic; all six patients showed faint eosin-5'-maleimide staining. In western blotting of erythrocyte membrane proteins, all six patients (three with β-spectrin, two with ankyrin, and one with SLC4A1 anomalies) showed low-molecular-weight peptide fragments, which were confirmed by mass spectrometry in the region corresponding to the band 3 protein. The two patients with an ankyrin gene anomaly exhibited severe anaemia, and two patients with simultaneous SLC4A1, SPTB, and UGT1A1 anomalies exhibited mild anaemia and hyperbilirubinemia.

DISCUSSION

We determined the relationship among clinical features, cytochemical parameters, and gene anomalies in six patients with newly diagnosed HS while referring to previously published cases.

CONCLUSION

These findings reveal a close relationship between clinical features and membrane characteristics in HS, which can facilitate diagnosis and inform treatment.

Analysis of erythrocyte membrane proteins in patients with hereditary spherocytosis and other types of haemolytic anaemia

OBJECTIVES

In order to investigate the pathophysiology of erythrocyte membrane proteins, 10 patients (6 pre- and 4 post-splenectomy) with hereditary spherocytosis (HS) and other patients with haemolytic anaemia were examined.

METHODS

The membrane proteins were analysed by biochemical and mass spectrometry.

RESULTS

Reductions in the extracellular membrane of band 3 protein by eosin-5'-maleimide (EMA) binding test were greater in patients with pre-splenectomy HS than in patients with post-splenectomy HS, other types of haemolytic anaemia, and controls. Compared to patients with haemolytic anaemia and healthy controls, the band 3 protein of patients with HS pre- or post-splenectomy was more easily decomposed with N-glycosidase F and by mass spectrometry interactions with degraded low-molecular-weight spectrin and ankyrin. The resulting fragments were observed more frequently in pre-splenectomy than post-splenectomy HS. Haemoglobin-derived peptides were present in patients with haemoglobinopathy (Hb Evans, Hb Sabine) but not in those with haemolytic anaemia and healthy controls.

CONCLUSION

Haemolysis in patients with HS occurred because the fragile proteins in erythrocytes (band 3, spectrin, and ankyrin) collapsed due to compression during blood circulation in the spleen. Further, haemolysis in patients with haemoglobinopathy occurred owing to membrane damage due to combined spectrin, band 3 with denatured haemoglobin in the vessel during blood circulation.

Exome sequencing confirms molecular diagnoses in 38 Chinese families with hereditary spherocytosis

Hereditary spherocytosis (HS), the most common cause of congenital hemolytic anemia, is caused by deficiency of the erythrocyte membrane proteins. Five causative genes (ANK1, SPTB, SPTA1, SLC4A1, and EPB42) have been identified. To date, molecular genetic studies have been performed in different populations, including the American, European, Brazilian, Japanese and Korean populations, whereas only a few studies have been described in the Chinese population. Here, by reanalysis of the exome data, we revealed causative mutations and established a definitive diagnosis of HS in all 38 Chinese families. We found 34 novel mutations and four reported mutations in three known HS-causing genes-17 in ANK1, 17 in SPTB and four in SLC4A1, suggesting that ANK1 and SPTB are the major genes in Chinese patients with HS. All of the ANK1 or SPTB mutations, scattered throughout the entire genes, are non-recurrent; and most of them are null mutations, which might cause HS via a haploinsufficiency mechanism. De novo mutations in ANK1 or SPTB often occur with an unexpected high frequency (87.5% and 64.2%, respectively). Our study updates our knowledge about the genetic profile of HS in Chinese and shows that family-based, especially parent-offspring trio, sequencing analysis can help to increase the diagnostic power and improve diagnostic efficiency.