Clinical utility of targeted next-generation sequencing panel in routine diagnosis of hereditary hemolytic anemia: A national reference laboratory experience.

INTRODUCTION: Hereditary hemolytic anemias (HHA) comprise a heterogeneous group of disorders resulting from defective red blood cell (RBC) cytoskeleton, RBC enzyme deficiencies, and hemoglobin (Hb) synthesis disorders such as thalassemia or sideroblastic anemia. MATERIALS AND METHODS: Our hemolytic anemia diagnostic next-generation sequencing (NGS) panel includes 28 genes encoding RBC cytoskeletal proteins, membrane transporter, RBC enzymes, and certain bilirubin metabolism genes. The panel covers the complete coding region of these genes, splice junctions, and, wherever appropriate, deep intronic or regulatory regions are also included. Four hundred fifty-six patients with unexplained hemolytic anemia were evaluated using our NGS panel between 2015 and 2019. RESULTS: We identified pathogenic/likely pathogenic variants in 111/456 (24%) patients that were responsible for the disease phenotype (e.g., moderate to severe hemolytic anemia and hyperbilirubinemia). Approximately 40% of the mutations were novel. As expected, 45/456 (10%) patients were homozygous for the promoter polymorphism in the UGT1A1 gene, A(TA)7 TAA (UGT1A1*28). 8/45 homozygous UGT1A1*28 cases were associated with additional pathogenic mutations causing hemolytic anemia, likely exacerbating hyperbilirubinemia. The most common mutated genes were membrane cytoskeleton genes SPTA1, and SPTB, followed by PKLR. Complex interactions between SPTA1 low expression alleles, alpha-LELY and alpha-LEPRA alleles, and intragenic SPTA1 variants were associated with hereditary pyropoikilocytosis and autosomal recessive hereditary spherocytosis in 23/111 patients. CONCLUSIONS: Our results demonstrate that hemolytic anemia is underscored by complex molecular interactions of previously known and novel mutations in RBC cytoskeleton/enzyme genes, and therefore, NGS should be considered in all patients with clinically unexplained hemolytic anemia and in neonates with hyperbilirubinemia. Moreover, low expression alleles alpha-LELY and alpha-LEPRA should be included in all targeted HHA panels.

Transient neonatal hemolytic anemia due to the novel gamma globin gene mutation HBG2:C.290T>C, p.Leu97Pro (hemoglobin Wareham).

Unstable gamma globin variants can cause transient neonatal hemolytic anemia. We have identified a novel variant in a newborn who presented with jaundice and anemia requiring phototherapy and red blood cell transfusion. The patient was found to be heterozygous for the mutation HGB2:c.290T>C, p.Leu97Pro, which we have termed hemoglobin (Hb) Wareham. This substitution is expected to generate an unstable hemoglobin with increased oxygen affinity based on the homologous mutation previously described in the beta globin gene, which is termed as Hb Debrousse. The patient fully recovered by 9 months of age as expected with the transition from fetal to adult hemoglobin.

Thirty-five males with severe (Class 1) G6PD deficiency (c.637G>T) in a North American family of European ancestry.

In North America, jaundiced neonates are not usually tested for G6PD deficiency if the family is of European ancestry. However, we describe such a family where ≥35 males have had severe (Class I) G6PD deficiency. Many of the jaundiced neonates did not have this diagnosis considered, at least three of whom developed bilirubin neurotoxicity. Over seven generations 35 affected males were identified. Three developed signs of kernicterus spectrum disorder; three had exchange transfusions for hyperbilirubinemia; and nine received one or more blood transfusions during childhood.

JAK2 ex13InDel drives oncogenic transformation and is associated with chronic eosinophilic leukemia and polycythemia vera.

The V617F mutation in the JH2 domain of Janus kinase 2 (JAK2) is an oncogenic driver in several myeloproliferative neoplasms (MPNs), including essential thrombocythemia, myelofibrosis, and polycythemia vera (PV). Other mutations in JAK2 have been identified in MPNs, most notably exon 12 mutations in PV. Here, we describe a novel recurrent mutation characterized by a common 4-amino-acid deletion and variable 1-amino-acid insertion (Leu583-Ala586DelInsSer/Gln/Pro) within the JH2 domain of JAK2. All 4 affected patients had eosinophilia, and both patients with Leu583-Ala586DelInsSer fulfilled diagnostic criteria of both PV and chronic eosinophilic leukemia (CEL). Computational and functional studies revealed that Leu583-Ala586DelInsSer (herein referred to as JAK2ex13InDel) deregulates JAK2 through a mechanism similar to JAK2V617F, activates signal transducer and activator of transcription 5 and extracellular signal-regulated kinase, and transforms parental Ba/F3 cells to growth factor independence. In contrast to JAK2V617F, JAK2ex13InDel does not require an exogenous homodimeric type 1 cytokine receptor to transform Ba/F3 cells and is capable of activating ß common chain family cytokine receptor (interleukin-3 receptor [IL-3R], IL-5R, and granulocyte-macrophage colony stimulating factor receptor) signaling in the absence of ligand, with the maximum effect observed for IL-5R, consistent with the clinical phenotype of eosinophilia. Recognizing this new PV/CEL-overlap MPN has significant clinical implications, as both PV and CEL patients are at high risk for thrombosis, and concomitant cytoreduction of red cells, neutrophils, and eosinophils may be required for prevention of thromboembolic events. Targeted next-generation sequencing for genes recurrently mutated in myeloid malignancies in patients with unexplained eosinophilia may reveal additional cases of Leu583-Ala586DelInsSer/Gln/Pro, allowing for complete characterization of this unique MPN.

Bone marrow necrosis in pediatric malignancies: 10-Year retrospective review and review of literature.

Bone marrow necrosis (BMN) is a rare pathologic finding, but when encountered is most often associated with malignancy. In adults, its presence correlates with an inferior prognosis, however in children the prognostic implication is unclear. We performed a retrospective review of 3,760 bone marrow specimens in patients ≤18 years over a 10-year period. BMN was identified in less than 1% of specimens and only in patients with leukemia, lymphoma, or neuroblastoma. BMN contributed to a delay in diagnosis; however, advanced medical imaging may serve as a tool to localize nonnecrotic areas for bone marrow sampling, facilitating an expedited diagnosis.

Two Clonally Distinct B-Cell Lymphomas Reveal the Diagnosis of XLP1 in a Male Child and His Asymptomatic Male Relatives: Case Report and Review of the Literature.

X-linked lymphoproliferative disease type 1 (XLP1) is a primary immunodeficiency disorder caused by pathogenic variants in the SH2D1A gene (SH2 domain containing protein 1A). Patients with XLP1 may present acutely with fulminant infectious mononucleosis, hemophagocytic lymphohistiocytosis, and/or B-cell non-Hodgkin lymphoma (B-NHL). We report a boy who developed 2 clonally distinct B-NHL 4 years apart and was found to have previously unrecognized XLP1. The report highlights the importance of clonal analysis and XLP1 testing in males with presumed late recurrences of B-NHL, and the role of allogeneic stem cell transplant (allo-SCT) in XLP1 patients and their affected male relatives.

Dizygotic twins with prolonged jaundice and microcytic, hypochromic, hemolytic anemia with pyropoikilocytosis.

Dizygotic twin males, born at 34 weeks gestation, had prolonged jaundice, microcytic, hypochromic anemia, FABarts hemoglobin, elevated end-tidal CO, and blood films consistent with hereditary pyropoikilocytosis. DNA sequencing revealed both had a heterozygous alpha spectrin (SPTA1) mutation (c.460_462dup) inherited from their asymptomatic mother, plus a 3-base pair duplication in alpha globin (HBA2) (c.364_366dupGTG) inherited from their asymptomatic father.

δ-Globin Chain Variants Associated with Decreased Hb A2 Levels: A National Reference Laboratory Experience.

High prevalence of hemoglobin (Hb) disorders mandates national programs for screening and genetic counseling in many countries. Increased Hb A2 levels are commonly associated with ß-thalassemias, however, various disorders including alteration of δ chains may result in decreased production of Hb A2, thus hindering the diagnosis of ß-thalassemias. The reported data reflect the experience of a large reference laboratory in the United States. In the current study, we have attempted to assess the prevalence and also tried to characterize the identified mutations in the HBD gene resulting in decreased Hb A2 levels. In our cohort, 1.6% of 6486 patients were found to have Hb A2 values of <1.9%. Bidirectional sequencing of the HBD gene demonstrated mutations in 20 cases (19.0% of the individuals with decreased Hb A2). In addition to the previously reported variants, one novel mutation (Hb A2-Utah or HBD: c.46T>C).

Molecular Understanding of Severe Cases of ß-Thalassemia in the Nablus Region, West Bank, Palestine.

Hemoglobinopathies are common inherited monogenic diseases that are likely to remain a serious regional health problem where thalassemias and sickle cell disease are prevalent. In regions where recessive alleles for hemoglobinopathy disorders are present with high consanguinity rates, such as in Palestine, coinheritance of two different genetic defects becomes anticipated and prevalent. In this report, we characterize the molecular variants of the HBB gene for 16 patients with transfusion-dependent anemia registered at the Thalassemia Patient Friends Society in Nablus governorate, West Bank, Palestine. Analysis revealed that 63.0% (10/16) of the patients were homozygous for ß-thalassemia (ß-thal), IVS-I-6 (T>C) (HBB: c.92+6T>C) or IVS-I-110 (G>A) (HBB: c.93-21G>A); 19.0% (3/16) homozygous for sickle cell disease or Hb S (HBB: c.20A>T, p.Glu6Val); 13.0% (2/16) were double heterozygotes for Hb S/ß-thal, (HBB: c.20A>T/HBB: c.92G>C) and HBB: c.20A>T/HBB: c.321_322insG; and one case was a compound heterozygote for ß-thal, codon 39 (C>T) (HBB: c.118C>T) and IVS-I-110. The most common mutation reported in the 16 patients was IVS-I-6 (0.38), followed by IVS-I-110 (0.28) Hb S (0.25) and 0.03 each for codon 39, codons 106/107 (HBB: c.321_322insG) and Hb Monroe (HBB: c.92G>C). In conclusion, in Palestine, a variety of intricate inheritance patterns are encountered in clinical practice.

Diagnosis of Hemoglobinopathy and ß-Thalassemia by 21 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Tandem Mass Spectrometry of Hemoglobin from Blood.

BACKGROUND: Hemoglobinopathies and thalassemias are the most common genetically determined disorders. Current screening methods include cation-exchange HPLC and electrophoresis, the results of which can be ambiguous because of limited resolving power. Subsequently, laborious genetic testing is required for confirmation. METHODS: We performed a top-down tandem mass spectrometry (MS/MS) approach with a fast data acquisition (3 min), ultrahigh mass accuracy, and extensive residue cleavage by use of positive electrospray ionization 21 Tesla Fourier transform ion cyclotron resonance-tandem mass spectrometry (21 T FT-ICR MS/MS) for hemoglobin (Hb) variant de novo sequencing and ß-thalassemia diagnosis. RESULTS: We correctly identified all Hb variants in blind analysis of 18 samples, including the first characterization of homozygous Hb Himeji variant. In addition, an Hb heterozygous variant with isotopologue mass spacing as small as 0.0194 Da (Hb AD) was resolved in both precursor ion mass spectrum (MS1) and product ion mass spectrum (MS2). In blind analysis, we also observed that the abundance ratio between intact δ and ß subunits (δ/ß) or the abundance ratio between intact δ and α subunits (δ/α) could serve to diagnose ß-thalassemia trait caused by a mutation in 1 HBB gene. CONCLUSIONS: We found that 21 T FT-ICR MS/MS provides a benchmark for top-down MS/MS analysis of blood Hb. The present method has the potential to be translated to lower resolving power mass spectrometers (lower field FT-ICR mass spectrometry and Orbitrap) for Hb variant analysis (by MS1 and MS2) and ß-thalassemia diagnosis (MS1).

Addressing the diagnostic gaps in pyruvate kinase deficiency: Consensus recommendations on the diagnosis of pyruvate kinase deficiency.

Pyruvate kinase deficiency (PKD) is the most common enzyme defect of glycolysis and an important cause of hereditary, nonspherocytic hemolytic anemia. The disease has a worldwide geographical distribution but there are no verified data regarding its frequency. Difficulties in the diagnostic workflow and interpretation of PK enzyme assay likely play a role. By the creation of a global PKD International Working Group in 2016, involving 24 experts from 20 Centers of Expertise we studied the current gaps in the diagnosis of PKD in order to establish diagnostic guidelines. By means of a detailed survey and subsequent discussions, multiple aspects of the diagnosis of PKD were evaluated and discussed by members of Expert Centers from Europe, USA, and Asia directly involved in diagnosis. Broad consensus was reached among the Centers on many clinical and technical aspects of the diagnosis of PKD. The results of this study are here presented as recommendations for the diagnosis of PKD and used to prepare a diagnostic algorithm. This information might be helpful for other Centers to deliver timely and appropriate diagnosis and to increase awareness in PKD.

Prostate cancer risk regions at 8q24 and 17q24 are differentially associated with somatic TMPRSS2:ERG fusion status.

Molecular and epidemiological differences have been described between TMPRSS2:ERG fusion-positive and fusion-negative prostate cancer (PrCa). Assuming two molecularly distinct subtypes, we have examined 27 common PrCa risk variants, previously identified in genome-wide association studies, for subtype specific associations in a total of 1221 TMPRSS2:ERG phenotyped PrCa cases. In meta-analyses of a discovery set of 552 cases with TMPRSS2:ERG data and 7650 unaffected men from five centers we have found support for the hypothesis that several common risk variants are associated with one particular subtype rather than with PrCa in general. Risk variants were analyzed in case-case comparisons (296 TMPRSS2:ERG fusion-positive versus 256 fusion-negative cases) and an independent set of 669 cases with TMPRSS2:ERG data was established to replicate the top five candidates. Significant differences (P < 0.00185) between the two subtypes were observed for rs16901979 (8q24) and rs1859962 (17q24), which were enriched in TMPRSS2:ERG fusion-negative (OR = 0.53, P = 0.0007) and TMPRSS2:ERG fusion-positive PrCa (OR = 1.30, P = 0.0016), respectively. Expression quantitative trait locus analysis was performed to investigate mechanistic links between risk variants, fusion status and target gene mRNA levels. For rs1859962 at 17q24, genotype dependent expression was observed for the candidate target gene SOX9 in TMPRSS2:ERG fusion-positive PrCa, which was not evident in TMPRSS2:ERG negative tumors. The present study established evidence for the first two common PrCa risk variants differentially associated with TMPRSS2:ERG fusion status. TMPRSS2:ERG phenotyping of larger studies is required to determine comprehensive sets of variants with subtype-specific roles in PrCa.

Acute neonatal bilirubin encephalopathy in the State of Utah 2009-2018.

Herein we report a case series of seven newborn infants, all apparently well at birth, who in the period since 2009 were cared for in the State of Utah with acute bilirubin encephalopathy (ABE). This report summarizes our attempts to define common features of these seven through a state-wide voluntary registry, as a step toward devising new means of preventing such cases in the future. In previous reports of ABE, many of the affected neonates had no clearly defined explanation for their progressive hyperbilirubinemia. Our efforts to identify clear explanations in all seven cases included next generation DNA sequencing, testing a panel of 28 genes involved in bilirubin production and metabolism. We found that hemolytic disease was a unifying feature of these seven; two had DAT (+) Anti-D or anti-c hemolysis, while five had confirmed mutations in genes involved in bilirubin production and or metabolism that were previously unrecognized in these families.

Effect of treatment dose reductions in the setting of hand-foot syndrome on survival outcomes in patients with metastatic renal cell carcinoma treated with vascular endothelial growth factor receptor inhibitors.

Purpose Hand-foot syndrome is a common dose limiting toxicity of vascular endothelial growth factor receptor tyrosine kinase inhibitors used for treatment of patients with metastatic renal cell carcinoma. The effect of treatment dose reductions, in the context of hand-foot syndrome, on survival outcomes is reported. Methods This was a retrospective case series of patients receiving vascular endothelial growth factor receptor tyrosine kinase inhibitors from 1 January 2004 to 31 October 2013. The main outcomes were progression-free and overall survival in these patients experiencing hand-foot syndrome and undergoing treatment dose reductions. Univariate and multivariate analyses were conducted utilizing Kaplan-Meier method and COX Proportional Hazard model with landmark analyses at 2 months. Results Of the 120 patients evaluated, treatment dose reductions for any reason were required in 68 (56.7%) patients. The most common reasons for treatment dose reductions were mucositis, hand-foot syndrome, and fatigue. The median progression-free survival and overall survival were significantly longer in patients with hand-foot syndrome with or without treatment dose reductions as compared to those without hand-foot syndrome. Conclusions An improvement in survival outcomes was observed in metastatic renal cell carcinoma patients with treatment-associated hand-foot syndrome despite treatment dose reductions. These data need validation in a larger cohort to confirm the hypothesis that treatment dose reductions in the setting of hand-foot syndrome do not negatively impatient survival.

Neutrophil-lymphocyte ratio as a predictive biomarker for response to high dose interleukin-2 in patients with renal cell carcinoma.

BACKGROUND: Immunotherapy with high-dose interleukin-2 (HD-IL2) results in long-term survival in some metastatic renal cell carcinoma (mRCC) patients but has significant acute toxicities. Biomarkers predicting response to therapy are needed to better select patients most likely to benefit. NLR (absolute neutrophil count (ANC)/absolute lymphocyte count (ALC)) is a prognostic and predicative biomarker in various malignancies. The goal was to determine whether NLR can predict response to HD-IL2 in this setting. METHODS: Patients with clear cell mRCC treated with HD-IL2 were identified from an institutional database from 2003-2012. Baseline variables for the assessment of IMDC risk criteria, and neutrophil and lymphocyte count, were collected. Best response criteria were based on RECIST 1.0. Wilcoxon rank-sum test was used to evaluate the association of continuous baseline variables with disease control. NLR was stratified by ≤4 or >4. Progression free survival (PFS) and overall survival (OS) were estimated with the Kaplan-Meier method and Cox proportional hazard models assessed associations of NLR with survival. RESULTS: In 71 eligible patients, median NLR in those with an objective response (n = 14, 20%) was 2.3 vs 3.4 in those without (n = 57, 80%, p = 0.02). NLR ≤4 was associated with improved progression free and overall survival. After adjustment for IMDC risk criteria, NLR remained a significant predictor of OS (ANC/ALC ≤4 vs >4, HR 0.41, 95% CI 1.09-5.46, p = 0.03; ANC/ALC continuous variable per unit change in NLR, HR 1.08, 95% CI 1.01-1.14, p = 0.03). CONCLUSIONS: In this discovery set, NLR predicts overall survival in patients treated with HD-IL2 in mRCC, and may allow better patient selection in this setting. Data needs validation in an independent cohort.

Checkpoint inhibition in pediatric hematologic malignancies.

Immune surveillance comprising of adaptive and innate immune systems is naturally designed to eliminate cancer development; overexpression of inhibitory receptors and their ligands prevent this check and lead to evasion and hence cancer progression and metastasis. The use of tumor-specific monoclonal antibodies (MAbs) targeting these checkpoint regulators is promising and has led to this novel field of cancer immunotherapy. The first antibody directed against cytotoxic T-lymphocyte associated protein 4 (CTLA-4), ipilimumab, showed promising results in clinical trials and was approved by the US Food and Drug Administration (FDA) for the treatment of metastatic melanoma in 2011. Since then, various other immune checkpoint inhibitors are being studied in preclinical and clinical trial phases, targeting programmed-death-1 (PD-1) and its ligand programmed death ligand 1 (PD-L1), T cell lymphocyte activation gene-3 (LAG-3), and others. Results from clinical trials are promising, and currently this approach has proven effective and safe in patients with solid tumors and some hematological malignancies in adults. In general, CTLA-4 and PD-1 inhibitors are well tolerated; however, the augmented immune response enabled by this class of agents is associated with a unique group of side effects called immune-related adverse events (irAEs). Experience in pediatrics using immune checkpoint inhibitors for hematological malignancies is limited to Hodgkin's disease and non-Hodgkin's lymphoma as in the ongoing Children's Oncology Group (COG) protocol ADVL1412. Therapeutic advances in childhood leukemia and lymphoma (TACL) consortium will initiate an early phase clinical trial with PD-1 inhibitor nivolumab in relapsed/refractory acute myeloid leukemia (AML) in the next few months.

Loss of Major DNase I Hypersensitive Sites in Duplicated ß-globin Gene Cluster Incompletely Silences HBB Gene Expression.

We report an infant with sickle cell disease phenotype by biochemical analysis whose ß-globin gene (HBB) sequencing showed sickle cell mutation (HBBS ) heterozygosity. The proband has a unique head-to-tail duplication of the ß-globin gene cluster having wild-type (HBBA ) and HBBS alleles inherited from her father; constituting her HBBS /HBBS -HBBA genotype. Further analyses revealed that proband's duplicated ß-globin gene cluster (∼650 kb) encompassing HBBA does not include the immediate upstream locus control region (LCR) or 3' DNase I hypersensitivity (HS) element. The LCR interacts with ß-globin gene cluster involving long range DNA interactions mediated by various transcription factors to drive the regulation of globin genes expression. However, a low level of HBBA transcript was clearly detected by digital PCR. In this patient, the observed transcription from the duplicated, distally displaced HBBA cluster demonstrates that the loss of LCR and flanking 3'HS sites do not lead to complete silencing of HBB transcription.

Clinical utility of next-generation sequencing in the diagnosis of hereditary haemolytic anaemias.

Hereditary haemolytic anaemias are genetically and phenotypically heterogeneous disorders characterized by increased red cell destruction, with consequences ranging from innocuous to severe life-threatening anaemia. Diagnostic laboratories endeavour to assist clinicians reach the exact patient diagnosis by using tests principally based on morphological and biochemical techniques. However, these routine studies may be inconclusive, particularly in newborn infants and when transfusions have recently been administered. Large numbers and size of the potentially involved genes also impose a practical challenge for molecular diagnosis using routine sequencing approaches. To overcome these diagnostic shortcomings, we have utilized next-generation sequencing to provide a high-throughput, highly sensitive assay. We developed a panel interrogating 28 genes encoding cytoskeletal proteins and enzymes with sequencing coverage of the coding regions, splice site junctions, deep intronic and regulatory regions. We then evaluated 19 samples, including infants with unexplained extreme hyperbilirubinaemia and patients with transfusion-dependent haemolytic anaemia. Where possible, inheritance patterns of pathogenic mutations were determined by sequencing of immediate relatives. We conclude that this next-generation sequencing panel could be a cost-effective approach to molecular diagnosis of hereditary haemolytic anaemia, especially when the family history is uninformative or when routine laboratory testing fails to identify the causative haemolytic process.

Extension of overall survival beyond objective responses in patients with metastatic renal cell carcinoma treated with high-dose interleukin-2.

PURPOSE: In metastatic renal cell carcinoma (mRCC), survival benefit associated with objective response rates of 16-20 % with high-dose interleukin-2 (HDIL-2) is well established and discussed. Based on recently emerged data on efficacy of cancer immunotherapy, we hypothesized that the survival benefit with HDIL-2 extends beyond those achieving objective responses, i.e., to those who achieve stable disease as the best response to treatment. MATERIALS AND METHODS: All sequential treatment naïve mRCC patients treated with HDIL-2 at the University of Utah (1988-2013) and University of Michigan (1997-2013) were included. Best responses on treatment were associated with survival outcomes using log-rank and COX regression with a landmark analysis at 2 months. RESULTS: 391 patients (75 % male; median age 55 years) were included and belonged to the following prognostic risk categories: 20 % good, 64 % intermediate, and 15 % poor. Best responses on treatment were complete response (9 %), partial response (10 %), stable disease (32 %), progressive disease (42 %), and not evaluable for response (7 %). No significant differences in progression-free survival (HR 0.74, 95 % CI 0.48-1.1, p = 0.14) or overall survival (HR 0.66, 95 % CI 0.39-1.09, p = 0.11) were observed between patients achieving partial response versus stable disease. Significant differences in progression-free survival (HR 0.13, 95 % CI 0.09-0.22, p < 0.0001) and overall survival (HR 0.33, 95 % CI 0.23-0.48, p < 0.0001) were observed between patients achieving stable disease compared to those with progressive disease and who were not evaluable. CONCLUSIONS: Survival benefit with HDIL-2 is achieved in ~50 % patients and extends beyond those achieving objective responses.

Siblings with severe pyruvate kinase deficiency and a complex genotype.

Siblings presented as neonates with severe jaundice and transfusion-dependent hemolytic anemia. Next-generation sequencing revealed both to have three heterozygous mutations in the gene encoding erythrocyte pyruvate kinase (PKLR), plus a heterozygous splice mutation in the beta-spectrin gene (SPTB). In addition, both have a different 5th mutation in a gene encoding other erythrocyte membrane proteins. The asymptomatic parents and all three asymptomatic siblings have different sets of these mutations. © 2016 Wiley Periodicals, Inc.