Perforin defects of primary haemophagocytic lymphohistiocytosis in Japan

The perforin gene was analysed in 15 Japanese patients with primary haemophagocytic lymphohistiocytosis (HLH). Perforin gene defects were found in two out of eight patients with familial HLH (FHL), and one out of seven without affected siblings. Four novel mutations were identified. Compound heterozygous mutations (one FHL and one sporadic HLH) and only one allele mutation (one FHL) were defined. Flow cytometry revealed no perforin expression in CD8+ or CD56+ cells from a surviving patient with a mutation. The frequency of mutation was at least 20% of FHL in Japan. Flow cytometry for intracellular perforin may be useful for the screening of FHL2.     

难治性病毒感染和原发噬血细胞性淋巴组织细胞增多症相关基因突变研究

目的 研究难治性病毒感染或噬血细胞性淋巴组织细胞增多症(HLH)中免疫基因突变的发生率、类型及其临床特征.方法 采用基因测序方法 检测难治性病毒感染或HLH患者是否有原发性HLH相关的PRF1、UNC13D、STX11、STXBP2、SH2D1A和XIAP基因突变,并追踪其临床特点及转归.结果 共25例难治性病毒感染性疾病或HLH患者接受了基因突变筛查,其中13例检测到上述基因突变:PRF1突变6例,UNC13D突变3例,STX11、STXBP2、SH2D1A、XIAP突变各1例;其中6例起病表现为病毒相关性HLH,1例为原因不明HLH,4例为慢性活动性EB病毒(EBV)感染(CAEBV),2例为EBV相关性淋巴瘤.12例未检测出基因突变的患者中,4例为EBV相关HLH,其中1例发展为外周T细胞淋巴瘤,另8例为CAEBV.结论 原发性HLH相关免疫基因突变是难治性病毒感染或HLH的重要原因,大部分表现为HLH,部分患者以CAEBV或EBV相关淋巴瘤起病.基因检测是明确此类疾病诊断的有力证据.

Abstract：

Objective To study the type and corresponding clinical characteristics of primary hemophagocytic lymphohistocytosis (HLH) associated immune gene mutations in the refractory virus infection or HLH of unknown causes. Methods From December 2009 to July 2010, the patients with refractory virus infection or HLH of unknown causes were screened for the primary HLH associated immune genes mutations by DNA sequence analysis, including PRF1, UNC13D, STX11, STXBP2, SH2D1A and XIAP. The clinical characteristics and outcomes were followed up. Results Totally 25 patients with refractory virus infection or HLH of unknown causes were investigated for the 6 genes and 13 cases were found carrying gene mutations, composing of 6 of PRF1 mutation, 3 of UNC13D, and each one of STX11,XIAP, SH2D1A and STXBP2, respectively. Among the 13 cases with gene mutations, 5 suffered from Epstein-Barr virus associated HLH( EBV-HLH), 1 human herpes virus 7 associated HLH (HHV7-HLH),1 HLH without causes, 4 chronic activated EB virus infection (CAEBV) with 1 progressing to Hodgkin's lymphoma carrying abnormal chromosome of t ( 15; 17 ) (q22; q25 ) and hyperdiploid, 2 EBV associated lymphoma. Among the other 12 patients without gene mutation, 4 suffered from EBV-HLH with 1 progressing to peripheral T lymphoma, 8 suffered from CAEBV. Conclusions Primary HLH associated immune gene mutations are critical causes of refractory virus infection of unknown causes, most patients manifest as HLH,some cases appear in CAEBV and EBV associated lymphoma. DNA sequence analysis is helpful to early diagnosis and correct decision-making for treatment.     

Haemophagocytic lymphohistiocytosis: proposal of a diagnostic algorithm based on perforin expression

Haemophagocytic lymphohistiocytosis (HLH) is a rare, fatal disorder of early infancy. Mutations of the PRF1 gene have been identified in a subset of patients. However, the distinction between the different genetically determined and environmental subtypes of the disease remains a major issue to be solved. This may result in delayed or inappropriate application of bone marrow transplantation (BMT). We propose an algorithm that uses a combination of three rapid laboratory tests, i.e. perforin expression by peripheral lymphocytes, assessment of the behaviour of the 2B4 lymphocyte receptor and natural killer (NK) cell activity, to identify the different subgroups of HLH. In 19 patients diagnosed according to current criteria, we tested perforin expression, 2B4 receptor function and NK cell activity. PRF1 mutations were found in all seven patients showing absent perforin expression. In one male with abnormal behaviour of the 2B4 receptor, SH2D1A mutation confirmed the diagnosis of X-linked lymphoproliferative disease. Four patients with normal NK cell activity had evidence of associated infections. Of the seven with impaired NK cell activity, two had a probable genetically determined subtype of HLH and five appeared as sporadic, infection-associated cases. Improving the diagnostic approach may restrict the use of BMT, the only recognized curative treatment, to HLH patients with a documented poor prognosis while patients with milder disorders may be treated less intensively. Our flow chart could also lead to better selection of patients for specific gene analysis.     

Perforin gene mutations in adult-onset hemophagocytic lymphohistiocytosis

Perforin gene (PRF1) mutations cause the primary form of hemophagocytic lymphohistiocytosis (HLH). We report a genetic defect of PRF1 in a 62-year-old Japanese man with recurrent episodes of HLH. Sequencing of PRF1 from both peripheral blood mononuclear cells and nail clippings showed compound heterozygous mutation, including deletion of two base pairs at codons 1090 and 1091 (1090-1091delCT) and guanine-to-adenine conversion at nucleotide position 916 (916GAEA). Although primary HLH has been detected in infants and children, genetic mutation of PRF1 or other genes should be considered a differential diagnosis of HLH even in the elderly.     

A proportion of patients with lymphoma may harbor mutations of the perforin gene

Perforin mutations have been demonstrated in a proportion of patients diagnosed with the familial form of hemophagocytic lymphohistiocytosis (HLH). In the present study, we evaluated whether some patients with lymphoma sharing clinical characteristics with HLH might harbor mutations of the perforin gene. We analyzed 29 patients and found that 4 patients, who developed either Hodgkin or non-Hodgkin lymphoma, had biallelic mutations of the perforin gene. One of these 4 patients, a 19-year-old female with T-cell lymphoma, had a brother carrying the same mutations who developed HLH. In 2 of the 4 patients with biallelic mutations of the perforin gene, we evaluated perforin expression by flow cytometry and natural killer (NK) activity and both were found to be absent. Moreover, we documented the presence of monoallelic mutations of the perforin gene in 4 more patients. One of these 4 latter patients also carried a mutation of the Fas gene. These data indicate that perforin deficiency, either alone or in combination with other mutations of genes involved in lymphocyte survival or functional activity, may be present in patients with lymphoma. These findings suggest that perforin also plays a key role in the mechanisms of immune surveillance that prevent tumor growth and/or development.     

Review of hemophagocytic lymphohistiocytosis (HLH) in children with focus on Japanese experiences

Hemophagocytic lymphohistiocytosis (HLH) is characterized by fever and hepatosplenomegaly associated with pancytopenia, hypertriglyceridemia and hypofibrinogenemia. Increased levels of cytokines and impaired natural killer activity are biological markers of HLH. HLH can be classified into two distinct forms, including primary HLH, also referred to as familial hemophagocytic lymphohistiocytosis (FHL), and secondary HLH. Although FHL is an autosomal recessive disorder typically occurring in infancy, it is important to clarify that the disease may also occur in older patients. It is now considered that FHL is a disorder of T-cell function; moreover, clonal proliferation of T lymphocytes is observed in a few FHL patients, and cytotoxicity of these T lymphocytes for target cells is usually impaired. In 1999, perforin gene (PRF1) mutation was identified as a cause of 20-30% of FHL (FHL2) cases. In Japan, two specific mutations of PRF1 were also detected. Furthermore, in 2003, MUNC13-4 mutations were identified in some non-FHL2 patients (FHL3). Identification of other genes responsible for remaining cases is a major concern. Hematopoietic stem cell transplantation (HSCT) has been established as the only accepted curative therapy for FHL. Thus, appropriate diagnosis and prompt treatment with HSCT are necessary for FHL patients. Genetic analysis for PRF1 and MUNC13-4 and functional assay of cytotoxic T lymphocytes are recommended to be performed in each patient. In those patients displaying impaired cytotoxic function but lacking genetic defects, samples should be employed for identification of unknown genes. In the near future, an entire pathogenesis should be clarified in order to establish appropriate therapies including immunotherapy, HSCT and gene therapy.     

异基因造血干细胞移植治疗原发性噬血细胞综合征合并中枢神经系统病变一例报告及文献复习

目的 探讨原发性噬血细胞综合征（HLH）合并中枢神经系统病变诊断要点以及异基因造血干细胞移植（Allo-HSCT）治疗情况。 方法：对1例根据HLH-2004诊断标准确诊的原发性HLH合并中枢神经系统病变的病例临床特点进行分析,完善基因测序、免疫学指标检测和家系调查,进行Allo-HSCT。 结果：确诊11岁男性病例1例,表现为反复发热、全血细胞减少,脾大、骨髓中可见噬血现象,NK细胞活性下降（10.39%）。基因检测和家系调查显示患者携带分别来自父系和母系的PRF1基因的复杂杂合改变,两位胞姐各自携带不同突变位点;全家成员穿孔素蛋白表达量均有不同程度下降。病程中出现癫痫,头颅核磁共振提 示多发病变。确诊原发性HLH合并中枢神经系统病变。给予HLH-2004方案治疗后,接受胞姐HLA 5/10相合Allo-HSCT。目前移植后14个月,一般情况良好。 结论 对于合并中枢神经系统病变的原发性HLH,尽早进行Allo-HSCT是获得长期生存及治愈的唯一方法。     

A functional analysis of the putative polymorphisms A91V and N252S and 22 missense perforin mutations associated with familial hemophagocytic lymphohistiocytosis

Up to 60% of cases of the autosomal recessive immunodeficiency hemophagocytic lymphohistiocytosis (HLH) are associated with mutations in the perforin (PRF1) gene. In this study, we expressed wild-type and mutated perforin in rat basophil leukemia cells to study the effect on lytic function of the substitutions A91V and N252S (commonly considered to be neutral polymorphisms) and 22 perforin missense substitutions first identified in HLH patients. Surprisingly, we found that A91V perforin was expressed at reduced levels compared with wild-type perforin, resulting in partial loss of lytic capacity. In contrast, expression and function of N252S-substituted perforin were normal. Most HLH-associated mutations resulted in protein degradation (probably due to misfolding) and complete loss of perforin activity, the exception being R232H, which retained approximately 30% wild-type activity. Several other mutated proteins (H222Q, C73R, F157V, and D313V) had no detectable lytic activity but were expressed at normal levels, suggesting that their functional defect might map downstream at the level of the target cell membrane. One further perforin substitution identified in an HLH patient (V183G) was normally expressed and displayed normal lysis. This report represents the first systematic functional analysis of HLH-associated missense mutations and the 2 most common perforin polymorphisms.     

Perforin expression in cytotoxic lymphocytes from patients with hemophagocytic lymphohistiocytosis and their family members.

Mutations in the perforin gene have been described in some patients with hemophagocytic lymphohistiocytosis (HLH), but the role of perforin defects in the pathogenesis of HLH remains unclear. Four-color flow cytometric analysis was used to establish normal patterns of perforin expression for control subjects of all ages, and patterns of perforin staining in cytotoxic lymphocytes (natural killer [NK] cells, CD8(+) T cells, CD56(+) T cells) from patients with HLH and their family members were studied. Eleven unrelated HLH patients and 19 family members were analyzed prospectively. Four of the 7 patients with primary HLH showed lack of intracellular perforin in all cytotoxic cell types. All 4 patients showed mutations in the perforin gene. Their parents, obligate carriers of perforin mutations, had abnormal perforin-staining patterns. Analysis of cytotoxic cells from the other 3 patients with primary HLH and remaining family members had normal percentages of perforin-positive cytotoxic cells. On the other hand, the 4 patients with Epstein-Barr virus-associated HLH typically had depressed numbers of NK cells but markedly increased proportions of CD8(+) T cells with perforin expression. Four-color flow cytometry provides diagnostic information that, in conjunction with evidence of reduced NK function, may speed the identification of life-threatening HLH in some families and direct further genetic studies of the syndrome.     

Mutations of the hemophagocytic lymphohistiocytosis-associated gene UNC13D in a patient with systemic juvenile idiopathic arthritis

The clinical syndromes of hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are both characterized by dysregulated inflammation with prolonged fever, hepatosplenomegaly, coagulopathy, hematologic cytopenias, and evidence of hemophagocytosis in the bone marrow or liver. While HLH is either inherited or acquired, children with severe rheumatic diseases, most notably systemic juvenile idiopathic arthritis, are at risk for MAS. The phenotypic similarity between HLH and MAS raises the possibility that they share common pathogenetic mechanisms. Familial forms of HLH have been attributed to mutations in the genes encoding perforin (PRF1) and Munc13-4 (UNC13D), among others, and are characterized by defective cytotoxic lymphocyte function. While some patients with systemic JIA have decreased levels of perforin protein expression and natural killer (NK) cell function, mutations of HLH-associated genes in patients with systemic JIA have not been reported. We report the case of an 8-year-old girl with systemic JIA without MAS who was found to have compound heterozygous mutations of UNC13D and reduced NK cell cytotoxic function. This case broadens the range of clinical phenotypes attributable to UNC13D mutations and offers new insights into the etiology and pathogenesis of systemic JIA.     

Mutations of the hemophagocytic lymphohistiocytosis–associated gene UNC13D in a patient with systemic juvenile idiopathic arthritis

The clinical syndromes of hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are both characterized by dysregulated inflammation with prolonged fever, hepatosplenomegaly, coagulopathy, hematologic cytopenias, and evidence of hemophagocytosis in the bone marrow or liver. While HLH is either inherited or acquired, children with severe rheumatic diseases, most notably systemic juvenile idiopathic arthritis, are at risk for MAS. The phenotypic similarity between HLH and MAS raises the possibility that they share common pathogenetic mechanisms. Familial forms of HLH have been attributed to mutations in the genes encoding perforin (PRF1) and Munc13‐4 (UNC13D), among others, and are characterized by defective cytotoxic lymphocyte function. While some patients with systemic JIA have decreased levels of perforin protein expression and natural killer (NK) cell function, mutations of HLH‐associated genes in patients with systemic JIA have not been reported. We report the case of an 8‐year‐old girl with systemic JIA without MAS who was found to have compound heterozygous mutations of UNC13D and reduced NK cell cytotoxic function. This case broadens the range of clinical phenotypes attributable to UNC13D mutations and offers new insights into the etiology and pathogenesis of systemic JIA.     

Subtyping of natural killer cell cytotoxicity deficiencies in haemophagocytic lymphohistocytosis provides therapeutic guidance

The familial form of haemophagocytic lymphohistiocytosis (HLH) is a fatal disease, with allogeneic stem cell transplantation (SCT) being the only curative treatment. In contrast, patients with secondary (infection-associated) HLH usually do not require SCT. Since it often is difficult to distinguish primary and secondary HLH, we wanted to identify a tool that provides guidance on whether SCT is required. The clinical outcome of 65 HLH patients was analysed in relation to the recently reported four types of defects in natural killer (NK)-cell cytotoxicity in HLH. None (0%) of the 36 patients with NK-cell deficiency type 3 attained a sustained (1-year) remission after stopping therapy without receiving SCT, in contrast to 45% (13/29) non-type 3 patients (P < 0.001). Most type 3 patients (22/36) underwent SCT (14/22, 64% are alive), whereas 11 of 14 that did not receive SCT died, and the three others had received HLH-therapy during the last year of follow-up. Of 54 patients analysed for perforin expression and/or mutation, the five with perforin deficiency were all type 3 patients. The data suggests that HLH patients with NK-cell deficiency type 3 will probably require SCT to survive. Thus, NK-cell deficiency classification may provide valuable guidance in judging whether an HLH-patient needs SCT.     

Perforin gene analaysis in an Iranian family with familial hemophagocytic lymphohistiocytosis

Perforin gene (PRF1) mutations have been reported in 20-30% of patients with familial hemophagocytic lymphohistiocytosis (FHL), an immune disorder of infancy and early childhood. Cytotoxic T and natural killer (NK) cell activities are remarkably reduced or absent in FHL patients. We report the first cases of familial hemophagocytic lymphohistiocytosis in an Iranian family with two siblings. Exons 2 and 3 of the PRF1 gene were analyzed by polymerase chain reaction (PCR) amplification and direct sequencing. Perforin gene mutation(s) were detected in none of the cases. The result of our study indicates that not much evidence is present concerning a correlation between perforin gene defects and familial hemophagocytic lymphohistiocytosis etiology in these cases.     

Genetic subtypes of familial hemophagocytic lymphohistiocytosis: correlations with clinical features and cytotoxic T lymphocyte/natural killer cell functions

Mutations of the perforin (PRF1) and MUNC13-4 genes distinguish 2 forms of familial hemophagocytic lymphohistiocytosis (FHL2 and FHL3, respectively), but the clinical and biologic correlates of these genotypes remain in question. We studied the presenting features and cytotoxic T lymphocyte/natural killer (CTL/NK) cell functions of 35 patients for their relationship to distinct FHL subtypes. FHL2 (n = 11) had an earlier onset than either FHL3 (n = 8) or the non-FHL2/FHL3 subtype lacking a PRF1 or MUNC13-4 mutation (n = 16). Deficient NK cell activity persisted after chemotherapy in all cases of FHL2, whereas some patients with FHL3 or the non-FHL2/FHL3 subtype showed partial recovery of this activity during remission. Alloantigen-specific CTL-mediated cytotoxicity was deficient in FHL2 patients with PRF1 nonsense mutations, was very low in FHL3 patients, but was only moderately reduced in FHL2 patients with PRF1 missense mutations. These findings correlated well with Western blot analyses showing an absence of perforin in FHL2 cases with PRF1 nonsense mutations and of MUNC13-4 in FHL3 cases, whereas in FHL2 cases with PRF1 missense mutations, mature perforin was present in low amounts. These results suggest an association between the type of genetic mutation in FHL cases and the magnitude of CTL cytolytic activity and age at onset.     

Perforin gene mutations in patients with acquired aplastic anemia

Perforin is a cytolytic protein expressed mainly in activated cytotoxic lymphocytes and natural killer cells. Inherited perforin mutations account for 20% to 40% of familial hemophagocytic lymphohistiocytosis, a fatal disease of early childhood characterized by the absence of functional perforin. Aplastic anemia, the paradigm of immune-mediated bone marrow failure syndromes, is characterized by hematopoietic stem cell destruction by activated T cells and Th1 cytokines. We examined whether mutations in the perforin gene occurred in acquired aplastic anemia. Three nonsynonymous PRF1 mutations among 5 unrelated patients were observed. Four of 5 patients with the mutations showed some hemophagocytosis in the bone marrow at diagnosis. Perforin protein levels in these patients were very low or absent, and perforin granules were completely absent. Natural killer (NK) cell cytotoxicity from these patients was significantly decreased. Our data suggest that PRF1 genetic alterations help explain the aberrant proliferation and activation of cytotoxic T cells and may represent genetic risk factors for bone marrow failure.     

Functional consequences of perforin gene mutations in 22 patients with familial haemophagocytic lymphohistiocytosis

Familial haemophagocytic lymphohistiocytosis (FHL), an inherited form of haemophagocytic lymphohistiocytosis (HLH) syndrome, is characterized by the overwhelming activation of T lymphocytes and macrophages invariably leading to death in the absence of treatment. FHL is a heterogeneous autosomal recessive disorder, with one known causative gene which codes for perforin, a cytotoxic effector protein. In this study, we have characterized the genotype and phenotype of 14 unrelated families with perforin deficiency. Four new missense mutations of the perforin gene were identified. In every case, perforin gene mutations led to undetectable intracellular perforin expression within cytotoxic cells, while some residual T-cell cytotoxic activity could be associated with certain missense mutations. Clinical and biological analyses did not differentiate between patients with nonsense or missense mutations, although age at diagnosis, which tended to be similar within members of the same family, was delayed in patients from two families belonging to the second group. In one case, consequences of perforin deficiency, diagnosed at birth, could be assessed prior to onset of clinical manifestations. No evidence for T-cell activation could be shown, suggesting that an exogenous event is required to trigger the disease manifestation. Control assessment of perforin expression and cytotoxic assays by lymphocytes from young children led to the conclusion that perforin content of natural killer cells could be a reliable diagnostic test at any age. Altogether, these data enabled a better characterization of perforin deficiency and its consequences, and defined reliable diagnostic tools.     

Fatal immune dysregulation due to a gain of glycosylation mutation in lymphocyte perforin

Mutations in the perforin gene (PRF1) are a common cause of the fatal immune dysregulation disorder, familial hemophagocytic lymphohistiocytosis (type 2 FHL, FHL2). Here we report a female infant born with biallelic PRF1 mutations: a novel substitution, D49N, and a previously identified in-frame deletion, K285del. We assessed the effects of each mutation on the cytotoxicity of human NK cells in which the expression of endogenous perforin was ablated with miR30-based short hairpin (sh) RNAs. Both mutations were detrimental for function, thereby explaining the clinically severe presentation and rapidly fatal outcome. We demonstrate that D49N exerts its deleterious effect by generating an additional (third) N-linked glycosylation site, resulting in protein misfolding and degradation in the killer cell. Our data provide a rationale for treating some cases of type 2 familial hemophagocytic lymphohistiocytosis, based on the pharmacologic inhibition or modification of glycosylation.     

Hemophagocytic lymphohistiocytosis due to germline mutations in SH2D1A, the X-linked lymphoproliferative disease gene

The hemophagocytic lymphohistiocytoses (HLH) comprise a heterogeneous group of disorders characterized by dysregulated activation of T cells and macrophages. Although some patients with HLH harbor perforin gene mutations, the cause of the remaining cases is not known. The phenotype of HLH bears a strong resemblance to X-linked lymphoproliferative disease (XLP), an Epstein-Barr virus (EBV)-associated immunodeficiency resulting from defects in SH2D1A, a small SH2 domain-containing protein expressed in T lymphocytes and natural killer cells. Here it is shown that 4 of 25 male patients with HLH who were examined harbored germline SH2D1A mutations. Among these 4 patients, only 2 had family histories consistent with XLP. On the basis of these findings, it is suggested that all male patients with EBV-associated hemophagocytosis be screened for mutations in SH2D1A. Patients identified as having XLP should undergo genetic counseling, and be followed long-term for development of lymphoma and hypogammaglobulinemia.     

Immunophenotypic analysis of Epstein-Barr virus (EBV)-infected CD8(+) T cells in a patient with EBV-associated hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a severe and often fatal condition characterized by uncontrolled activation of T cells and macrophages. In Epstein-Barr virus (EBV)-associated HLH (EBV-HLH), the pathogenic roles of ectopic EBV infection in the T-cell population and of clonal proliferation of EBV-infected T cells has been described. However, the immunophenotype of EBV-infected T cells has not been fully characterized. Here we describe a case of EBV-HLH presenting with a massive clonal proliferation of CD8(+) T cells with TCR VB14. Analysis of in situ hybridization for EBV-encoded small RNA1 showed that only CD8(+) T cells harbored EBV in this patient. The EBV-infected TCR VB14(+) CD8(+) T cells exhibited unique immunophenotypic features including lacked CD5 expression and a markedly bright expression of HLA-DR. After initiation of treatment with prednisolone, etoposide, and cyclosporin A, the percentage of infected cells declined progressively in parallel with other serum markers such as ferritin. These findings suggest that lacking expression of CD5 on CD8(+) T cells with specific TCR VB may serve as a useful marker of dysregulated T-cell activation and proliferation in EBV-HLH.     

Characteristic features of the genotype and phenotype of hereditary spherocytosis in the Japanese population

Hereditary spherocytosis (HS) is the most common hemolytic anemia of congenital origin in the Japanese population. Among 844 cases of 520 kindred with congenital red cell membrane disorders studied at the Kawasaki Medical School in the last 25 years (1975-1999), 407 cases (48.2%) of 215 kindred had HS. Among the recent 60 kindred with HS, autosomal dominant (AD) transmission was proven in 19. The remaining 41 non-AD HS included 1) homozygous patients with autosomal recessive inheritance, 2) HS patients with de novo gene mutations, and 3) mild HS with AD inheritance. The extent of clinical severity in the non-AD HS cases was nearly identical to that in the AD cases. The incidence of membrane protein abnormalities in our 60 Japanese HS kindred was unique: there were lower ankyrin deficiencies (7%), moderate band 3 deficiencies (20%), and much higher protein 4.2 deficiencies (45%), with 28% of unknown etiology. The incidence of membrane protein deficiencies corresponded to that determined by gene analyses; i.e., mutations mostly in band 3 and/or in protein 4.2 genes and fewer ankyrin gene mutations. In the band 3 gene, 11 mutations pathognomonic for HS were identified (3 frameshift and 8 missense mutations). There were 5 mutations of the protein 4.2 gene (3 missense mutations, 1 nonsense mutation, and 1 splicing mutation) pathognomonic for HS. On the other hand, 2 missense mutations were detected in the ankyrin gene in this study. The genetic abnormalities in our HS patients correlated well with the phenotypic ultrastructural abnormalities of red cell membranes in situ. Ankyrin mutations (ankyrin Marburg and ankyrin Stuttgart with frameshift mutations) were associated mostly with a disrupted cytoskeletal network, and band 3 mutations (band 3 Kagoshima with frameshift mutation) typically demonstrated anomalies of intramembrane particles (IMPs). Protein 4.2 mutations (homozygotes of protein 4.2 Nippon) with complete protein 4.2 deficiency showed abnormalities of both the cytoskeletal network and IMPs.