Trp207Gly in platelet glycoprotein Ibalpha is a novel mutation that disrupts the connection between the leucine-rich repeat domain and the disulfide loop structure and causes Bernard-Soulier syndrome

BACKGROUND

Bernard-Soulier syndrome (BSS) is a severe inherited bleeding disorder that is caused by a defect in glycoprotein (GP)Ib-IX-V complex, the platelet membrane receptor for von Willebrand factor.

PATIENTS

The diagnosis of BSS was made in two members of a Bukharian Jewish family who had life-long thrombocytopenia associated with mucocutaneous bleeding manifestations.

METHODS AND RESULTS

Flow cytometry and Western blot analyses showed only trace amounts of GPIb and GPIX on the patients' platelets. Sequence analysis of the GPIbalpha gene revealed a homozygous T > G transversion at nucleotide 709 predicting Trp207Gly substitution in the mature protein. Introduction of the mutation into a mammalian expression construct abolished the surface expression of GPIbalpha in transfected baby hamster kidney cells. The crystal structure of the N-terminus of GPIbalpha (PDB: 1SQ0) indicates that Trp207 is completely buried and located in a disulfide loop structure that interacts with the leucine-rich repeat (LRR) domain.

CONCLUSION

A novel mutation, Trp207Gly, causes BSS and predicts disruption of the interaction between a disulfide loop and the LRR domain that is essential for the integrity of GPIbalpha structure.

Diversity of Glanzmann thrombasthenia in southern India: 10 novel mutations identified among 15 unrelated patients

BACKGROUND

Glanzmann thrombasthenia (GT) is a congenital bleeding disorder caused by either a lack or dysfunction of the platelet integrin alphaIIbbeta3.

OBJECTIVES

To determine the molecular basis of GT in patients from southern India.

PATIENTS

Fifteen unrelated patients whose diagnosis was consistent with GT were evaluated.

RESULTS

Platelet surface expression of alphaIIbbeta3 was < 10%, 10%-50%, and > 50% of controls in five, nine, and one patient(s), respectively. Immunoblotting of the platelet lysates showed no alphaIIb in 14 patients, and no beta3 in 10 patients, although severely reduced in four patients. Platelet fibrinogen was undetectable in 13 patients, and severely reduced in one patient. One patient showed normal surface alphaIIbbeta3 expression, and normal alphaIIb, beta3 and fibrinogen levels in the lysate. Ten novel candidate disease-causing mutations were identified in 11 patients. The missense mutations included Gly128Ser, Ser287Leu, Gly357Ser, Arg520Trp, Leu799Arg in alphaIIb, and Cys575Gly in beta3. We have already shown that Gly128Ser, Ser287Leu, and Gly357Ser mutations variably affect alphaIIbbeta3 surface expression. The Cys575Gly mutation may disrupt the disulphide link with Cys586 to cause the GT phenotype. The molecular pathology of the other missense mutations is not clear. Two nonsense mutations, Trp-16Stop and Glu715Stop in alphaIIb, and a 7-bp deletion (330-336TCCCCAG) in beta3 are predicted to result in truncated proteins. An IVS15(-1)G --> A mutation in alphaIIb induced a cryptic splice site as confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Thirteen polymorphisms were also identified (five in alphaIIb and eight in beta3), among which five were novel.

CONCLUSIONS

While identifying a significant number of novel mutations causing GT, this study confirms the genetic heterogeneity of the disorder in southern India.

Rare bleeding disorders

Deficiencies of coagulation factors other than factor VIII and factor IX (afibrinogenemia, FII, FV, FV+FVIII, FVII, FX, FXI, FXIII) that cause bleeding disorders (RBDs) are inherited as autosomal recessive traits and are rare, with prevalences in the general population varying between 1 in 500,000 and 1 in 2 million for the homozygous forms. As a consequence of the rarity of these deficiencies, the type and severity of bleeding symptoms, the underlying molecular defects, and the actual management of bleeding episodes are not as well established as for hemophilia A and B. The study of the genetic basis of these disorders could represent an important tool for prevention through prenatal diagnosis. Treatment of patients with RBDs during bleeding episodes or surgery is a challenge because of the lack of experience and the paucity of data. For some deficiency factor concentrates are still non available and severe complications can occur. These complications can be minimized by assessment of risks of bleeding and thrombosis, use of haemostatic means other than blood components or no therapy at all. The RBDs pose a problem for guideline writers because there are no suitable clinical trials to supply good evidence for how these people are best treated. The lack of adequate information on clinical manifestations, treatment and genetic basis of RBDs could be improved by the collection of data in an International Database (http://www.rbdd.org), linkable to others previously published. This could be a useful tool to fill the gap between clinical data and clinical practice. This article reviews the genetic basis of RBDs, problems and complications of treatment, problems in the preparation of suitable guidelines for treatment and the future perspectives of the International Registry on RBDs.

Prerequisites for recombinant factor VIIa-induced thrombin generation in plasmas deficient in factors VIII, IX or XI

BACKGROUND

Recombinant factor VIIa (rFVIIa) used for the treatment of hemophilia A or B patients with an inhibitor is hemostatically effective because it induces thrombin generation (TG), despite grossly impaired FVIII- and FIX-dependent amplification of FX activation. Tissue factor (TF) and or activated platelets were shown to be essential for the rFVIIa activity.

OBJECTIVE

To evaluate the relative effects of TF and phospholipids on rFVIIa-induced TG in FVIII-, FIX- and FXI-deficient plasmas.

METHODS

Phospholipids had an independent effect that was augmented by TF. The contribution of blood-borne TF in FVIII-, FIX- and FXI-deficient plasma to rFVIIa-induced TG was demonstrated by removing microparticles and use of anti-TF antibodies.

RESULTS

At increasing concentrations of rFVIIa, the dependence of rFVIIa-induced TG on TF declined, but the presence of phospholipids was essential. rFVIIa was also shown to activate purified FIX and FX in the presence of phospholipids and absence of TF. rFVIIa-induced TG was dramatically augmented in FVIII- or FIX-deficient plasma in which the level of FVIII or FIX was increased to 1 or 2 U dL(-1).

CONCLUSIONS

The data indicate that rFVIIa-induced TG is affected by TF, phospholipids, rFVIIa concentration, and the presence of FVIII and FIX.

New observations on factor XI deficiency

Factor (F) XI is an injury-related bleeding tendency that commonly occurs when trauma involves tissues rich in fibronolytic activators. Severe FXI deficiency is defined when the activity of FXI in plasma is less than 15 U dL(-1). The disorder is inherited as an autosomal recessive trait manifesting in homozygotes or compound heterozygotes, and infrequently in heterozygotes. So far 53 mutations in the gene of FXI have been described and four of them were found to be prevalent in Ashkenazi Jews, Iraqi Jews, Basques or the English population. For each of the four mutations a founder effect was discerned. Inhibitors can develop in patients with FXI level < 1U dL(-1) who were exposed to plasma which seriously complicates their management during surgery. No correction of a prolonged aPTT by normal plasma is indicative of the presence of an inhibitor. In contrast to patients with haemophilia A, severe FXI deficiency provides no protection against myocardial infarction. In patients with severe FXI deficiency undergoing surgery, fresh frozen plasma is the treatment of choice. FXI concentrates can also be used but cause thrombosis in approximately 10% of patients, particularly those with cardiovascular disease. Recombinant FVIIa has successfully prevented bleeding during or after surgery in patients with FXI inhibitors.

Thrombophilic factors are not the leading cause of thrombosis in Behçet's disease

BACKGROUND

Venous and arterial thromboses occur in patients with Behçet's disease and are associated with significant morbidity and mortality. Studies on a possible association between the occurrence of thrombosis and thrombophilia in patients with this disease have been controversial.

OBJECTIVE

To determine the prevalence of the most common thrombophilias and dyslipidaemia in patients with Behçet's disease with and without thrombosis.

METHODS

Blood samples from 107 patients with Behçet's disease who had or did not have thrombosis were analysed for factor V Leiden, prothrombin G20210A polymorphism, methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, factor VIII level, homocysteine and C reactive protein concentrations, dyslipidaemia, and plasma glucosylceramide.

RESULTS

There was no difference between patients with and without thrombosis in the prevalence of prothrombin G20210A polymorphism, factor V Leiden, homozygous MTHFR C677T, or plasma concentrations of homocysteine, C reactive protein, or glucosylceramide. In contrast, patients with thrombosis were found to have significantly higher mean levels of factor VIII, total cholesterol, triglycerides, VLDL cholesterol, and apolipoproteins B-100, C-II, and C-III than those without thrombosis. Multistepwise logistic regression analysis showed that triglyceride concentration was the best marker associated with thrombosis (p = 0.008), with an estimated odds ratio of 1.58 (95% confidence interval, 1.09 to 2.30) for a difference of 40 mg/dl.

CONCLUSIONS

Thrombophilia does not seem to play a major role in the tendency to thrombosis in Behçet's disease. However, dyslipidaemia, predominantly hypertriglyceridaemia, might be a risk factor.

Severe factor XI deficiency caused by a Gly555 to Glu mutation (factor XI-Glu555): a cross-reactive material positive variant defective in factor IX activation

During normal hemostasis, the coagulation protease factor (F)XIa activates FIX. Hereditary deficiency of the FXIa precursor, FXI, is usually associated with reduced FXI protein in plasma, and circulating dysfunctional FXI variants are rare. We identified a patient with < 1% normal plasma FXI activity and normal levels of FXI antigen, who is homozygous for a FXI Gly555 to Glu substitution. Gly555 is two amino acids N-terminal to the protease active site serine residue, and is highly conserved among serine proteases. Recombinant FXI-Glu555 is activated normally by FXIIa and thrombin, and FXIa-Glu555 binds activated factor IX similarly to wild type FXIa (FXIa(WT)). When compared with FXIa(WT), FXIa-Glu555 activates factor IX at a greatly reduced rate ( approximately 400-fold), and is resistant to inhibition by antithrombin. Interestingly, FXIa(WT) and FXIa-Glu555 cleave the small tripeptide substrate S-2366 with comparable k(cat)s. Modeling indicates that the side chain of Glu555 significantly alters the electrostatic charge around the active site, and would sterically interfere with the interaction between the FXIa S2' site and the P2' residues on factor IX and antithrombin. FXI-Glu555 is the first reported example of a naturally occurring FXI variant with a significant defect in FIX activation.

Characterization of mutations causing factor VII deficiency in 61 unrelated Israeli patients

Inherited factor (F)VII deficiency is rare in most populations but relatively common in Israel. The aim of this study was to characterize the molecular and functional defect in unrelated Israeli patients with FVII deficiency. Mutations were identified by direct sequencing of PCR-amplified genomic DNA fragments. Selected mutations were expressed in baby hamster kidney (BHK) cells and tested for binding to tissue factor (TF), activation by FXa and activation of FX. In 61 patients with FVII deficiency, the causative mutation in the FVII gene was discerned. The predominant mutation found in this and a previously reported cohort of 27 unrelated patients in Israel was Ala244Val substitution; of 121 independent mutant alleles defined in all 88 patients ascertained in Israel, 102 (84%) bore this alteration. Eleven additional mutations were identified of which one, Cys22Arg, is novel. Expression of the mutations in BHK cells revealed that four (Ala244Val, 11128delC, Leu300Pro and Cys22Arg) were cross-reacting material (CRM)- negative, and three (Ala294Val, Cys310Phe and Phe24del) were CRM-positive. As predicted by modeling, we observed no binding to TF of FVII Phe24del, diminished binding of FVII Cys310Phe and normal binding of FVII Ala294Val. The main defect of FVII Ala294Val was its inability to activate FX in the presence of TF. Coexpression of Ala294Val and Arg353Gln, a polymorphism known to affect FVII secretion, did not reveal an additive effect on FVII secretion, while coexpression of Ala244Val and Arg353Gln did yield an additive effect.

Seven novel mutations in the factor XIII A-subunit gene causing hereditary factor XIII deficiency in 10 unrelated families

BACKGROUND

Hereditary factor (F)XIII deficiency is a rare bleeding disorder mostly due to mutations in FXIII A subunit.

OBJECTIVES

We studied the molecular basis of FXIII deficiency in patients from 10 unrelated families originating from Israel, India and Tunisia.

METHODS

Exons 2-15 of genomic DNA consisting of coding regions and intron/exon boundaries were amplified and sequenced. Structural analysis of the mutations was undertaken by computer modeling.

RESULTS

Seven novel mutations were identified in the FXIIIA gene. The propositus from the Ethiopian-Jewish family was found to be a compound heterozygote for two novel mutations: a 10-bp deletion in exon 12 at nucleotides 1652-1661 (followed by 22 altered amino acids and termination codon) and Ala318Val mutation. The propositus of the Tunisian family was homozygous for C insertion after nucleotide 863 within a stretch of six cytosines of exon 7. This insertion results in generation of eight altered amino acids followed by a termination codon downstream. The propositus from Indian-Jewish origin was found to be homozygous for G to T substitution at IVS 11 [+1] resulting in skipping of exons 10 and 11. In addition to the Ala318Val mutation, three of the novel mutations identified are missense mutations: Arg260Leu, Thr398Asn and Gly210Arg each occurring in a homozygous state in an Israeli-Arab and two Indian families, respectively.

CONCLUSIONS

Structure-function correlation analysis by computer modeling of the new missense mutations predicted that Gly210Arg will cause protein misfolding, Ala318Val and Thr398Asn will interfere with the catalytic process or protein stability, and Arg260Leu will impair dimerization.

A novel Phe171Cys mutation in integrin alpha causes Glanzmann thrombasthenia by abrogating alphabeta complex formation

BACKGROUND

Glanzmann thrombasthenia (GT) is an autosomal recessive bleeding disorder characterized by lack of platelet aggregation induced by most agonists. The disease is caused by mutations in either alpha(IIb)[glycoprotein (GP) IIb] or beta(3) (GPIIIa) genes that lead to a lack or dysfunction of the integrin alpha(IIb)beta(3) which serves as a fibrinogen receptor.

PATIENTS

Mucocutaneous bleeding manifestations and platelet dysfunction consistent with GT were observed in three members of a Cypriot family: a 3-year-old proband, her father and her paternal uncle.

OBJECTIVE

To determine the molecular basis of GT in this family and to characterize possible biochemical and structural defects.

RESULTS

Analysis of the patients' platelets by fluorescence-activated cell sorting demonstrated trace amounts of beta(3), no alpha(IIb) and no alpha(IIb)beta(3) on the membrane. Sequence analysis revealed a novel T607G transversion in exon 5 of the alpha(IIb) gene predicting a Phe171Cys alteration that created a PstI recognition site. All three patients were homozygous for the mutation, the mother and paternal grandparents of the proband were heterozygous, whereas 110 healthy subjects lacked this transversion. Chinese hamster ovary cells cotransfected with cDNAs of mutated alpha(IIb) and wild-type beta(3) failed to express alpha(IIb)beta(3) as shown by immunoprecipitation and immunohistochemistry experiments. Structural analysis of the alpha(IIb)beta(3) model, which was based on the crystal structure of alpha(v)beta(3), indicated that Phe171 plays an essential role in the interface between the beta-propeller domain of alpha(IIb) and the betaA domain of beta(3).

CONCLUSIONS

A novel Phe171Cys mutation in the alpha(IIb) gene of patients with GT is associated with abrogation of alpha(IIb)beta(3) complex formation.

A common ancestral mutation (C128X) occurring in 11 non-Jewish families from the UK with factor XI deficiency

Factor XI (FXI) deficiency is a mild bleeding disorder that is particularly common in Ashkenazi Jews, but has been reported in all populations. In Jews, two FXI gene (F11) mutations (a stop codon in exon 5, E117X, type II, and a point mutation in exon 9, F283L, type III) are particularly common, but in other populations a variety of different mutations have been described. In the Basque region of France one mutation, C38R in exon 3, was found in eight of 12 families studied, haplotype analysis suggesting a founder effect. In the course of screening 78 unrelated individuals (including 15 Jewish and 12 Asian) we have found 10 Caucasian non-Jewish patients with the mutation C128X in exon 5. Individuals were investigated because of a personal or family history of bleeding, or finding a prolonged activated partial thromboplastin time. Individuals negative for the type II and type III mutations were screened by a combination of SSCP and heteroduplex analysis. The C128X mutation was found in 10 families (one previously described). Among three individuals with severe FXI deficiency, one was homozygous for the C128X mutation, and two were compound heterozygotes for the C128X and another mutation; other individuals were carriers of the C128X mutation. This is a nonsense mutation producing a truncated protein; individuals have FXI antigen levels concordant with FXI coagulant activity. Haplotype analysis of 11 families, including a further kindred previously reported from the USA, but which originally came from the UK (in which the index patient was homozygous for C128X), suggests a founder effect.

Inherited factor XI deficiency confers no protection against acute myocardial infarction

BACKGROUND AND PURPOSE

Factor XI (FXI) contributes to thrombin generation thereby affecting fibrin formation and to down regulation of fibrinolysis by activation of thrombin-activatable fibrinolysis inhibitor (TAFI). The purpose of this study was to evaluate whether patients with severe FXI deficiency are protected against acute myocardial infarction (AMI).

METHODS

The incidence of AMI in patients with severe FXI deficiency (FXI activity less than 15 U dL(-1)) whose age was 35 years or more was compared to the incidence of AMI in age and gender matched persons of the general population. Atherosclerotic risk factors were assessed in FXI deficient patients and blood was tested for prothrombotic parameters such as FV Leiden, prothrombin G20210A, lupus anticoagulant, and platelet membrane polymorphisms. The common mutations causing FXI deficiency in Jews were also examined.

RESULTS

Of 96 patients with severe FXI deficiency (55 women and 41 men) 16 had a history of AMI (6 women and 10 men). The median age at the time of AMI was 64.5 for women and 58 for men. The calculated annual rate of AMI in men was similar to the expected in the general Israeli population, whereas in women it was almost 2-fold higher, but this difference did not reach statistical significance. One or more atherosclerotic risk factors were observed in 13 of 16 patients (81.3%) with AMI compared to 44 of 79 patients (55.7%) without AMI (P < 0.001). The frequency distributions of platelet polymorphisms and of prothrombotic polymorphisms were not different between patients with severe FXI deficiency who experienced or not an AMI. None of the patients had lupus anticoagulant. The common genotypes which cause FXI deficiency in Jews were similarly distributed in patients with and without AMI.

CONCLUSIONS

Severe FXI deficiency does not confer protection against AMI.

Methionine synthase A2756G and methylenetetrahydrofolate reductase A1298C polymorphisms are not risk factors for idiopathic venous thromboembolism

Hyperhomocysteinemia is a defined risk factor for venous thromboembolism (VTE). Several polymorphisms of genes encoding for enzymes acting in the remethylation pathway of homocysteine metabolism, ie, methionine synthase (MS) A2756G, methylenetetrahydrofolate reductase (MTHFR) C677T and MTHFR A1298C, can cause increased homocysteine levels particularly in patients with deficiencies of folic acid, vitamin B6, or B12 and hence be potential risk factors for VTE. Indeed, homozygous MTHFR C677T was shown to be a mild risk factor for VTE by some, but not by all, investigators. In this study, we assessed the risk exerted by MS A2756G and MTHFR A1298C in a cohort of patients with idiopathic venous thromboembolism. Homozygosities for MS A2756G and MTHFR A1298C were not found to be statistically significant risk factors for VTE. In addition, no interactions were observed among MS A2756G, MTHFR A1298C and MTHFR C677T in conferring a risk of VTE.

Molecular characterization of four novel mutations causing factor VII deficiency

INTRODUCTION

Hereditary deficiency of factor VII (FVII) is a rare coagulation defect. We previously studied the molecular basis of the FVII deficiency in Israeli patients and found that the majority of them bore the Ala244Val mutation. In the present study we further analysed FVII deficient patients.

PATIENTS AND METHODS

Three patients with severe FVII deficiency (FVII activity < or =1%) and one with partial deficiency (25%) were studied. In all four patients, the FVII gene was amplified and sequenced.

RESULTS

Four novel mutations have been identified: IVS 2+1G-->C Phe 24 deletion, Leu300Pro and Arg277His. Homozygosity for the IVS2+1G-->C mutation was lethal, whereas homozygosity for the Phe 24 deletion was accompanied by a severe bleeding tendency. FVII modeling showed that Phe 24 is located in the Gla domain. Both Arg 277 and Leu 300 are within the catalytic domain, although Arg 277 is also involved in tissue factor binding.

CONCLUSION

We have analysed four mutations, two of which (IVS2+1G-->C, Phe 24 deletion) were associated with severe bleeding tendency in the homozygous state, facilitating prenatal diagnosis. Hypothetically, using FVII modeling, Arg 277 replacement by histidine may weaken the tissue factor, while deletion of Phe 24 and Leu300Pro mutation might be associated with abnormal folding of the Gla and catalytic domains, respectively.

Patients with Glanzmann thrombasthenia lacking platelet glycoprotein alpha(IIb)beta(3) (GPIIb/IIIa) and alpha(v)beta(3) receptors are not protected from atherosclerosis

BACKGROUND

Platelets have been suggested to play a role in the early development of atherosclerosis. As one test of this hypothesis, we assessed whether patients with Glanzmann thrombasthenia who lack platelet glycoprotein alpha(IIb)beta(3) (GPIIb/IIIa) complexes or both alpha(IIb)beta(3) and the more ubiquitous alpha(v)beta(3) cell membrane complexes are protected from development of atherosclerosis.

METHODS AND RESULTS

Seven patients with Glanzmann thrombasthenia, 45 to 66 years of age, underwent bilateral carotid artery ultrasonography and screening for risk factors of atherosclerosis. Findings consistent with early atherosclerosis evaluated by measurement of intima-media thickness and presence of atherosclerotic plaques were observed in 6 of the 7 patients. Intima-media thickness values higher than the 75th and 90th percentiles of age- and sex-matched white control subjects of the Atherosclerosis Risk in Communities (ARIC) study were observed in 30 and 8 of 56 carotid artery measurements, respectively. Five of the 6 patients with signs consistent with early atherosclerosis lacked both alpha(IIb)beta(3) and alpha(v)beta(3) complexes and 1 only lacked alpha(IIb)beta(3).

CONCLUSIONS

Glanzmann thrombasthenia does not protect affected individuals from development of atherosclerosis.

Cerebrovascular events in patients with significant stenosis of the carotid artery are associated with hyperhomocysteinemia and platelet antigen-1 (Leu33Pro) polymorphism

BACKGROUND AND PURPOSE

Although risk factors for carotid artery stenosis caused by atherosclerosis are known, it is unclear what triggers "activation" of the atherosclerotic plaques and the ensuing thromboembolic cerebral events. The aim of this study was to evaluate whether thrombophilic factors, platelet glycoprotein (GP) polymorphisms, and homocysteine are associated with a risk of ischemic events in patients with significant carotid stenosis.

METHODS

Consecutive patients with >/=50% carotid stenosis, whether symptomatic (with ipsilateral ischemic events) or asymptomatic, who were evaluated and followed in a neurovascular clinic were tested for plasma levels of homocysteine, C677T mutation in methylenetetrahydrofolate reductase, G20210A mutation of factor II, factor V Leiden, antiphospholipid antibodies, and polymorphisms of platelet membrane GP: human platelet antigen (HPA)-1, GP Ia (C807T), and GP Ib (variable number of tandem repeats, Kozak, and HPA-2).

RESULTS

Eighty-six asymptomatic and 67 symptomatic patients were evaluated. The former group was older (73.7+/-6.9 versus 69.5+/-9.1 years, P=0.02). Major risk factors for stroke were similar in both groups. In symptomatic patients versus asymptomatic patients, hyperhomocysteinemia was 3-fold more frequent (34.3% versus 12.8%, respectively; P=0.002) and HPA-1a/b was almost 2-fold more common (38.8% versus 20.9%, respectively; P=0.01). All other thrombophilic factors and platelet polymorphisms studied did not differ significantly between the 2 groups. Multivariate analysis revealed that hyperhomocysteinemia and the HPA-1a/b genotype conferred a significant risk of cerebral ischemic events, with odds ratios (95% CI) of 4.07 (1.7 to 9.7) and 3.4 (1.5 to 7.8), respectively.

CONCLUSIONS

Hyperhomocysteinemia and HPA-1a/b are independent risk factors for ischemic events in patients with significant carotid stenosis.

Identification and functional analysis of two novel mutations in the multidrug resistance protein 2 gene in Israeli patients with Dubin-Johnson syndrome

Dubin-Johnson syndrome (DJS) is an inherited disorder characterized by conjugated hyperbilirubinemia and is caused by a deficiency of the multidrug resistance protein 2 (MRP2) located in the apical membrane of hepatocytes. The aim of this study was to identify the mutations in two previously characterized clusters of patients with Dubin-Johnson syndrome among Iranian and Moroccan Jews and determine the consequence of the mutations on MRP2 expression and function by expression studies. All 32 exons and adjacent regions of the MRP2 gene were screened by polymerase chain reaction and DNA sequencing. Two novel mutations were identified in exon 25. One mutation, 3517A-->T, predicting a I1173F substitution, was found in 22 homozygous Iranian Jewish DJS patients from 13 unrelated families and a second mutation, 3449G-->A, predicting a R1150H substitution, was found in 5 homozygous Moroccan Jewish DJS patients from 4 unrelated families. Use of four intragenic dimorphisms and haplotype analyses disclosed a specific founder effect for each mutation. The mutations were introduced into an MRP2 expression vector by site-directed mutagenesis, transfected into HEK-293 cells, and analyzed by a fluorescence transport assay, immunoblot, and immunocytochemistry. Continuous measurement of probenecid-sensitive carboxyfluorescein efflux revealed that both mutations impaired the transport activity of MRP2. Immunoblot analysis and immunocytochemistry showed that MRP2 (R1150H) matured properly and localized at the plasma membrane of transfected cells. In contrast, expression of MRP2 (I1173F) was low and mislocated to the endoplasmic reticulum of the transfected cells. These findings provide an explanation for the DJS phenotype in these two patient groups. Furthermore, the close localization of the two mutations identify this region of MRP2 as important for both activity and processing of the protein.

Identification of a region in glycoprotein IIIa involved in subunit association with glycoprotein IIb: further lessons from Iraqi-Jewish Glanzmann thrombasthenia

The most frequent mutation causing Glanzmann thrombasthenia in Iraqi-Jews (IJ-1) is an 11-bp deletion in exon 13 of the glycoprotein (GP) IIIa gene. This deletion predicts a frameshift that results in the elimination of the C406-C655 disulfide bond and a premature termination codon shortly before the transmembrane domain. To determine the contribution of each of these alterations to the thrombasthenic phenotype, Chinese hamster ovary or baby hamster kidney cells were cotransfected with normal GPIIb complementary DNA (cDNA) and the following GPIIIa cDNAs: normal, cDNA bearing IJ-1 mutation, 2011T>A mutated cDNA predicting C655S (single-letter amino acid codes) substitution, and 2019A>T mutated cDNA predicting Stop657. Elimination of the C406-C655 disulfide bond by C655S substitution did not affect GPIIb/IIIa surface expression or binding of the transfected cells to immobilized fibrinogen, whereas elimination of the transmembrane and cytoplasmic domains in IJ-1 and Stop657 mutants prevented both surface expression and binding of the transfected cells to immobilized fibrinogen. Immunohistochemical staining and immunoprecipitation demonstrated that the elimination of amino acids 657-762 in IJ-1 and Stop657 prevented intracellular GPIIb/IIIa complex formation, and differential immunofluorescence staining of GPIIIa and cellular organelles suggested that the truncated uncomplexed GPIIIa protein was retained in the endoplasmic reticulum. Because the use of GPIIIa Stop693 and normal GPIIb cDNAs yielded GPIIb/IIIa complex formation, though with lower efficiency, it is suggested that amino acids 657-692 of GPIIIa are essential for the intracellular association of GPIIb and GPIIIa. (Blood. 2001;98:1063-1069)

High prevalence and impact of subnormal serum vitamin B12 levels in Israeli elders admitted to a geriatric hospital

BACKGROUND

The elderly are known to have higher rates of low and subnormal vitamin B12 levels than younger persons. Vitamin B12 deficiency has been extensively studied in the elderly, but primarily in outpatient settings. There is a paucity of data regarding the prevalence of low and low-normal B12 in frail, hospitalized, elderly patients, and its implications. Additionally, there is little information regarding vitamin B12 status in Israeli elders.

OBJECTIVES

The objectives of the study were to estimate the prevalence of low and borderline vitamin B12 levels among frail, hospitalized, elderly patients, and their clinical implications.

METHODS

We conducted a chart review, using a retrospective cohort design. The participants were 895 patients admitted to Harzfeld Medical Center in Gedera, Israel. Records were abstracted for vitamin B12 and Folic Acid levels, gastric disease, and outcomes including death, cognitive impairment and neurologic disease.

RESULTS

Six hundred and forty patients were eligible for the study. In 15% of the patients, vitamin B12 level was in the low range (<150pmol/L) and in 25% in the low-normal range (150-250pmol/L). Gastric disease and antacid use were not associated with the vitamin B12 status. Mortality was higher in the high vitamin B12 group (p=0.02), perhaps reflecting a selection toward higher acuity in this group. Cerebrovascular disease was more common in patients with lower vitamin B12 levels (p=0.046).

CONCLUSIONS

Forty percent of hospitalized elderly patients have low or borderline serum levels of vitamin B12, which may contribute to cerebrovascular disease and cognitive decline.