POS0361 DNA METHYLATION SIGNATURES CHARACTERIZE PSORIASIS AND PSORIATIC ARTHRITIS IN MONOZYGOTIC TWINS DISCORDANT FOR THE DISEASE

Background:

Psoriatic disease is a chronic inflammatory disorder spanning from skin disease (psoriasis) to psoriatic arthritis (PsA). The genetic background is insufficient to explain disease onset as illustrated by not very informative Genome Wide Association Studies and monozygotic (MZ) twin studies recently performed. It is strongly assumed that epigenetics may contribute to disease susceptibility modulating gene expression. DNA methylation has been found involved in several autoimmune inflammatory rheumatic diseases. Here we have analysed the DNA methylation profile of a selected cohort of MZ twins discordant for psoriasis/PsA.

Objectives:

To identify the methylome associated with psoriasis and PsA in the peripheral blood of MZ twins discordant for these conditions.

Methods:

Peripheral blood from 7 couples of MZ twins discordant for psoriatic disease was collected and DNA extracted for a genome-wide evaluation of the DNA methylation profile, with the Infinium MethylationEPIC BeadChip. Minfi and the packages of the Bioconductor were used to analyse the data obtained. Quality control and exclusion criteria were applied to the raw data having a final number of 762.451 probes, which accounts for 88% of the total.

Results:

The approach first identified 2564 differentially methylated positions (DMPs; *p<0.005) with 19 genes potentially affected (with at least two DMPs within 1 kb of distance), including SMAD3 and SMARCA4/BRG1 involved in the Interferon and TGFβ pathways. Gene Ontology (GO) analysis of DMP-associated genes showed a significative enrichment (*p<0.005) in transcription factor binding, transcription corepressor and transcription coactivator activity, SMAD binding and histone -lysine-N-methyltransferase activity. To further validate the results, 5’-methylcytosine immunoprecipitation (MedIP) followed by Real Time PCR was performed to assess the methylation level of SMAD3 and SMARCA4/BRG1 promoters in the same cohort of MZ twins. We found significantly DNA methylation enrichment in SMARCA4/BRG1 promoter in psoriatic disease twins (p<0.05). SMAD3 and SMARCA4/BRG1 mRNA expression was also assessed to evaluate any inverse correlation with promoter methylation level, on the MZ cohort used for the EPIC array (n=4) and on a cohort of PsA/Ps patients (n=8) and appropriate healthy controls (n=3). Reduced mRNA expression (p<0.05) was demonstrated for SMARCA4/BRG1 (n=4). Conversely, no changes were found for SMAD3.

Conclusion:

We report the first DNA methylation approach in MZ twins discordant for psoriatic disease. We believe that the observed changes in SMAD3 and SMARCA/BRG1 genes may suggest an epigenetic imbalance of chromatin remodelling factors involved in inflammation pathways with a potential role in PsA/psoriasis immunopathogenesis.

Disclosure of Interests:

None declared

Hepatic fibrinogen storage disease: identification of two novel mutations (p.Asp316Asn, fibrinogen Pisa and p.Gly366Ser, fibrinogen Beograd) impacting on the fibrinogen γ-module

BACKGROUND

Quantitative fibrinogen deficiencies (hypofibrinogenemia and afibrinogenemia) are rare congenital disorders characterized by low/unmeasurable plasma fibrinogen antigen levels. Their genetic basis is invariably represented by mutations within the fibrinogen genes (FGA, FGB and FGG coding for the Aα, Bβ and γ chains). Currently, only four mutations (p.Gly284Arg, p.Arg375Trp, delGVYYQ 346-350, p.Thr314Pro), all affecting the fibrinogen γ chain, have been reported to cause fibrinogen storage disease (FSD), a disorder characterized by protein aggregation, endoplasmic reticulum retention and hypofibrinogenemia.

OBJECTIVES

To investigate the genetic basis of FSD in two hypofibrinogenemic patients.

METHODS

The mutational screening of the fibrinogen genes was performed by direct DNA sequencing. The impact of identified mutations on fibrinogen structure was investigated by in-silico molecular modeling. Liver histology was evaluated by light microscopy, electron microscopy and immunocytochemistry.

RESULTS

Here, we describe two hypofibrinogenemic children with persistent abnormal liver function parameters. Direct sequencing of the coding portion of fibrinogen genes disclosed two novel FGG missense variants (p.Asp316Asn, fibrinogen Pisa; p.Gly366Ser, fibrinogen Beograd), both present in the heterozygous state and affecting residues located in the fibrinogen C-terminal γ-module. Liver sections derived from biopsies of the two patients were examined by immunocytochemical analyses, revealing hepatocyte cytoplasmic inclusions immunoreactive to anti-fibrinogen antibodies.

CONCLUSIONS

Our work strongly confirms the clustering of mutations causing FSD in the fibrinogen γ chain between residues 284 and 375. Based on an in-depth structural analysis of all FSD-causing mutations and on their resemblance to mutations leading to serpinopathies, we also comment on a possible mechanism explaining fibrinogen polymerization within hepatocytes.

Identification of a novel large deletion in a patient with severe factor V deficiency using an in-house F5 MLPA assay

Factor V (FV) deficiency is a rare autosomal recessive bleeding disorder caused by mutations in the F5 gene. FV-deficient patients in whom no mutation or only one mutation is found may harbour large gene rearrangements, which are not detected by conventional mutation screening strategies. The aim of this study was to develop and validate a multiplex ligation-dependent probe amplification (MLPA) assay for the detection of large deletions and duplications in the F5 gene. Twenty-two MLPA probes targeting 19 of the 25 exons and the upstream and downstream regions of the F5 gene were designed and tested in 10 normal controls, a patient with a known heterozygous deletion of F5 exons 1-7 (positive control) and 14 genetically unexplained FV-deficient patients. MLPA results were confirmed by digital PCR on a QuantStudio(™) 3D Digital PCR System. The F5-specific probes yielded a reproducible peak profile in normal controls, correctly detected the known deletion in the positive control and suggested the presence of a novel deletion of exons 9-10 in a patient with undetectable FV levels and only one identified mutation. Follow-up by chip-based digital PCR, long-range PCR and direct sequencing confirmed that this patient carried a heterozygous F5 deletion of 1823 bp extending from intron 8 to intron 10. Bioinformatics sequence analysis pinpointed repetitive elements that might have originated the deletion. In conclusion, we have developed and validated an MLPA assay for the detection of gross F5 gene rearrangements. This assay may represent a valuable tool for the molecular diagnosis of FV deficiency.

The spectrum of factor XI deficiency in Italy

Factor XI (FXI) deficiency is a rare inherited bleeding disorder invariably caused by mutations in the FXI gene. The disorder is rather frequent in Ashkenazi Jews, in whom around 98% of the abnormal alleles is represented by Glu117X and Phe283Leu mutations. A wide heterogeneity of causative mutations has been previously reported in a few FXI deficient patients from Italy. In this article, we enlarge the knowledge on the genetic background of FXI deficiency in Italy. Over 4 years, 22 index cases, eight with severe deficiency and 14 with partial deficiency, have been evaluated. A total of 21 different mutations in 30 disease-associated alleles were identified, 10 of which were novel. Among them, a novel Asp556Gly dysfunctional mutation was also identified. Glu117X was also detected, as previously reported from other patients in Italy, while again Phe283Leu was not identified. A total of 34 heterozygous relatives were also identified. Bleeding tendency was present in very few cases, being inconsistently related to the severity of FXI deficiency in plasma. In conclusion, at variance with other populations, no single major founder effect is present in Italian patients with FXI deficiency.

Functional characterization of a novel missense mutation identified in a Turkish patient affected by severe coagulation factor V deficiency

Factor V (FV) deficiency is a rare coagulation disorder, characterized by a bleeding phenotype varying from mild to severe. To date, 115 mutations have been described along the gene encoding for FV (F5) but only few of them have been functionally characterized. Aim of this study was the identification and the molecular characterization of genetic defects underlying severe FV deficiency in a 7-month-old Turkish patient. Mutation detection was performed by sequencing the whole F5 coding region, exon-intron boundaries and about 300 bp of the promoter region. Functional analysis of the identified missense mutation was conducted by transient expression of wild-type and mutant FV recombinant molecules in COS-1 cells. Two novel mutations: a missense (Pro132Arg) and a 1-bp deletion (Ile1890TyrfsX19) were identified in the F5 gene. While the frameshift mutation is responsible for the introduction of a premature stop codon, likely triggering F5 mRNA to nonsense-mediated mRNA degradation, the demonstration of the pathogenic role of the Pro132Arg mutation required an experimental validation. Expression experiments showed that the missense mutation causes a significant reduction in FV secretion and in the specific activity of the residual secreted molecule (77% and 78% decrease, respectively). This paper reports the identification of two novel mutations responsible for FV deficiency, thus widening the mutational spectrum of the F5 gene. The Pro132Arg mutation adds to the only other two functionally characterized missense defects in the FV A1 domain.

Alterations of mRNA processing and stability as a pathogenic mechanism in von Willebrand factor quantitative deficiencies

INTRODUCTION

von Willebrand disease (VWD) is an inherited bleeding disorder due to a deficiency or abnormality of von Willebrand factor (VWF), associated with heterogeneous phenotypes. While VWD mutations acting at the protein level have been deeply investigated, fewer data are available on genetic defects affecting VWF mRNA.

AIM

The aim of this study was to characterize the molecular mechanism underlying VWD in three patients.

METHODS

Mutational screening of the patients (P1-3) was accomplished by DNA sequencing of all VWF exons and splicing junctions. Platelet mRNA was analyzed by reverse-transcription (RT)-PCR and real-time RT-PCR.

RESULTS

P1 is a compound heterozygote for a c.1534-3C>A transversion in intron 13 and for a nonsense mutation (p.Q77X) in exon 4. P2 is heterozygous for a splicing mutation in intron 9 (c.1109+2T>C). RT-PCR assays on the patient's platelet RNA revealed three mRNA populations: (i) wild type; (ii) lacking exon 9; and (iii) lacking exons 8 and 9. P3 showed a novel homozygous splicing mutation in intron 46 (c.7770+1G>T), producing three different mRNA species: (i) retaining the first 25 bp of intron 46; (ii) skipping exon 46; and (iii) skipping exon 46 while retaining 5 bp of intron 45. Whenever possible, the effect of mutations on the levels of VWF transcripts was analyzed, showing that mRNA variants containing a premature termination codon are downregulated, probably by the nonsense-mediated mRNA decay pathway.

CONCLUSIONS

The identification of the genetic basis of VWD in three patients confirmed that mutations leading to null alleles in the VWF gene are associated with allele-specific mRNA degradation.

The association of factor V Leiden with myocardial infarction is replicated in 1880 patients with premature disease

AIMS

Gain-of-function variants of genes encoding coagulation factor V (F5 G1691A) and prothrombin (F2 G20210A) cause hypercoagulability and are established risk factors for venous thrombosis. A meta-analysis of 66,155 cases and 91,307 controls found that either polymorphism is associated with a moderately increased risk of coronary artery disease (CAD). Because genetic factors play a particularly important role when acute myocardial infarction (AMI) occurs in the young, we chose to replicate these results by investigating, in the frame of a case-control study, a large cohort of Italian patients who had AMI before the age of 45years.

METHODS AND RESULTS

In 1880 patients with AMI (1680 men and 210 women) and an equal number of controls, the minor A allele of F5 G1691A (2.6% frequency in cases and 1.7% in controls) was associated with an increased risk of AMI, the association remaining significant after adjustment for traditional risk factors (OR, 1.66; 95% CI, 1.15-2.38; P=0.006). The positive association with AMI for the minor A allele of F2 G20210A (2.5% frequency in cases and 1.9% in controls) did not reach statistical significance (OR, 1.32; 95% CI, 0.96-1.80; P=0.159).

CONCLUSIONS

In a large cohort of young AMI patients the gain-of-function variant F5 G1691A was associated with an increased risk of AMI. The findings on the variant F2 G20210A confirmed the previously reported results, but the association was statistically not significant. These data suggest that a number of young patients with AMI carry gene variants associated with a procoagulant phenotype.

Molecular genetics of quantitative fibrinogen disorders

Fibrinogen is a complex glycoprotein involved in the final step of the coagulation cascade as the precursor of fibrin monomers that participate in the formation of the haemostatic plug. Three genes (FGA, FGB, and FGG) clustered on chromosome 4q31.3-4q32.1 encode the three polypeptide chains (Aalpha, Bbeta, and gamma), which in a pairwise fashion form the hexameric circulating molecule. Among congenital fibrinogen deficiencies, quantitative defects (also called type I deficiencies; i.e. congenital afibrino-genemia [CAF] and hypofibrinogenemia) are characterized by the concomitant absence or reduction of coagulant activity and immunoreactive protein, while qualitative defects (type II deficiencies; i.e. dysfibrinogenemia and hypodysfibrino-genemia) show low clotting protein in contrast with normal or moderately reduced antigen. Patients affected by CAF (Mendelian Inheritance in Man, [MIM] #202400) or severe hypofibrinogenemia (MIM+134820, *134830, and *134850) may experience bleeding manifestations varying from mild to catastrophic. Although many cases of fibrinogen deficiencies have been described from a clinical point of view, only in a minority of cases the causal mutation was identified. The genetic defects so far described, most unique for any analyzed family, are invariantly located in the fibrinogen cluster; for only few of them the pathogenic role either at the protein or at the mRNA level has been investigated. This review, besides providing a concise description of the main structural and functional properties of fibrinogen and giving an overview of the clinical manifestations, the laboratory diagnosis and therapeutic approches, will be focused on the present knowledge on the genetic basis of quantitative fibrinogen deficiencies. Our systematic analysis of the available clinical and genetic data on these disorders evidences their high allelic heterogeneity, the existence of different pathogenic mechanisms, and the absence of strong genotype/phenotype correlations.

The molecular basis of quantitative fibrinogen disorders

Hereditary fibrinogen disorders include type I deficiencies (afibrinogenemia and hypofibrinogenemia, i.e. quantitative defects), with low or unmeasurable levels of immunoreactive protein; and type II deficiencies (dysfibrinogenemia and hypodysfibrinogenemia, i.e. qualitative defects), showing normal or altered antigen levels associated with reduced coagulant activity. While dysfibrinogenemias are in most cases autosomal dominant disorders, type I deficiencies are generally inherited as autosomal recessive traits. Patients affected by congenital afibrinogenemia or severe hypofibrinogenemia may experience bleeding manifestations varying from mild to severe. This review focuses on the genetic bases of type I fibrinogen deficiencies, which are invariantly represented by mutations within the three fibrinogen genes (FGA, FGB, and FGG) coding for the three polypeptide chains Aalpha, Bbeta, and gamma. From the inspection of the mutational spectrum of these disorders, some conclusions can be drawn: (i) genetic defects are scattered throughout the three fibrinogen genes, with only few sites appearing to represent relative mutational hot spots; (ii) several different types of genetic lesions and pathogenic mechanisms have been described in affected individuals (including gross deletions, point mutations causing premature termination codons, missense mutations affecting fibrinogen assembly/secretion, and uniparental isodisomy associated with a large deletion); (iii) the possibility to express recombinant fibrinogen mutants in eukaryotic cells is rapidly shedding light into the molecular mechanisms responsible for physiologic and pathologic properties of the molecule; (iv) though mutation analysis of the fibrinogen cluster does not yield precise information for predicting genotype/phenotype correlations, it still provides a valuable tool for diagnosis confirmation, identification of potential carriers, and prenatal diagnosis.

Genetic diagnosis of haemophilia and other inherited bleeding disorders

Inherited deficiencies of plasma proteins involved in blood coagulation generally lead to lifelong bleeding disorders, whose severity is inversely proportional to the degree of factor deficiency. Haemophilia A and B, inherited as X-linked recessive traits, are the most common hereditary hemorrhagic disorders caused by a deficiency or dysfunction of blood coagulation factor VIII (FVIII) and factor IX (FIX). Together with von Willebrand's disease, a defect of primary haemostasis, these X-linked disorders include 95% to 97% of all the inherited deficiencies of coagulation factors. The remaining defects, generally transmitted as autosomal recessive traits, are rare with prevalence of the presumably homozygous forms in the general population of 1:500,000 for FVII deficiency and 1 in 2 million for prothrombin (FII) and factor XIII (FXIII) deficiency. Molecular characterization, carrier detection and prenatal diagnosis remain the key steps for the prevention of the birth of children affected by coagulation disorders in developing countries, where patients with these deficiencies rarely live beyond childhood and where management is still largely inadequate. These characterizations are possible by direct or indirect genetic analysis of genes involved in these diseases, and the choice of the strategy depends on the effective available budget and facilities to achieve a large benefit. In countries with more advanced molecular facilities and higher budget resources, the most appropriate choice in general is a direct strategy for mutation detection. However, in countries with limited facilities and low budget resources, carrier detection and prenatal diagnosis are usually performed by linkage analysis with genetic markers. This article reviews the genetic diagnosis of haemophilia, genetics and inhibitor development, genetics of von Willebrand's disease and of rare bleeding disorders.

Inherited defects of coagulation factor V: the hemorrhagic side

Coagulation factor V (FV) is the protein cofactor required in vivo for the rapid generation of thrombin catalyzed by the prothrombinase complex. It also represents a central regulator in the early phases of blood clot formation, as it contributes to the anticoagulant pathway by participating in the downregulation of factor VIII activity. Conversion of precursor FV to either a procoagulant or anticoagulant cofactor depends on the local concentration of procoagulant and anticoagulant enzymes, so that FV may be regarded as a daring tight-rope walker gently balancing opposite forces. Given this dual role, genetic defects in the FV gene may result in opposite phenotypes (hemorrhagic or thrombotic). Besides a concise description on the structural, procoagulant and anticoagulant properties of FV, this review will focus on bleeding disorders associated with altered levels of this molecule. Particular attention will be paid to the mutational spectrum of type I FV deficiency, which is characterized by a remarkable genetic heterogeneity and by an uneven distribution of mutations throughout the FV gene.

Liver histology of an afibrinogenemic patient with the Bbeta-L353R mutation showing no evidence of hepatic endoplasmic reticulum storage disease (ERSD); comparative study in COS-1 cells of the intracellular processing of the Bbeta-L353R fibrinogen vs. the ERSD-associated gamma-G284R mutant

BACKGROUND

Type I fibrinogen deficiencies (hypofibrinogenemia and afibrinogenemia) are rare congenital disorders characterized by low or unmeasurable plasma fibrinogen antigen levels. Their genetic bases are represented by mutations within the three fibrinogen genes. Among the 11 reported missense mutations, a few have been characterized by expression studies and found to have an impaired fibrinogen assembly and/or secretion. Histopathological analyses were previously reported in two hypofibrinogenemic cases with discernible hepatic disease, revealing that both underlying mutations (gamma-Gly284Arg and gamma-Arg375Trp) were associated with hepatic fibrinogen endoplasmic reticulum storage disease (ERSD).

OBJECTIVE

The objective of this study was to investigate the liver histology in an afibrinogenemic patient, homozygous for the Bbeta-Leu353Arg mutation, and to study the intracellular processing of the mutant protein.

PATIENTS AND METHODS

Liver histology was evaluated by light microscopy, electron microscopy and immunocytochemistry. Intracellular processing of mutant fibrinogen was analyzed by pulse-chase labeling and immunoprecipitation experiments. Messenger RNA levels were determined by real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The histopathological characterization of the liver showed no signs of fibrinogen accumulation, a difference from the previously reported findings in two hypofibrinogenemic kindreds with ERSD. To evaluate whether the Bbeta-Leu353Arg mutation and the ERSD-associated gamma-Gly284Arg mutation affected intracellular fibrinogen trafficking differently, both mutant proteins were expressed in COS-1 cells. Bbeta-Leu353Arg led to a more severe secretion defect, but no differences that could explain phenotype-genotype correlation were found in the intracellular processing. Endoglycosidase-H analysis demonstrated a secretion block before translocation to the Golgi medial stacks. Real-time RT-PCR studies showed normal levels of the Bbeta mRNA in the patient's liver.

CONCLUSIONS

The results confirm that Bbeta-Leu353Arg is associated with impaired fibrinogen secretion, but not with hepatic ERSD.

Severe factor V deficiency: exon skipping in the factor V gene causing a partial deletion of the C1 domain

BACKGROUND

Severe factor V (FV) deficiency is a rare coagulation disorder, characterized by very low or unmeasurable plasma levels of functional and immunoreactive FV. Among rare inherited coagulopathies, FV deficiency is the least characterized from a molecular point of view (only 12 mutations have been reported).

OBJECTIVES

The aim of this work was to investigate, at the molecular level, the pathogenetic mechanisms responsible for a case of severe FV deficiency.

PATIENTS AND METHODS

A 19-year-old Iranian man showing unmeasurable FV activity and severely reduced FV antigen level in plasma was studied. Mutation screening was performed by sequencing. The effect of the identified mutation was investigated both at the mRNA and at the protein level.

RESULTS

Molecular analysis of the factor V (FV) gene identified a novel homozygous A-->T transversion at position + 3 of the donor splice site of intron 19 (IVS19 + 3A-->T). Production of mutant mRNA in HeLa cells demonstrated that this mutation causes the entire exon 19 to be skipped from the FV mRNA. The mutant processed transcript codes for a deleted FV, lacking the first 24 amino acids of the C1 domain. Expression of the mutant FV protein in COS-1 cells showed that the deleted protein was synthesized but not secreted; moreover, the intracellular amount of deleted FV was reduced compared to wild type, suggesting intracellular degradation of mutant FV.

CONCLUSIONS

This work reports the molecular characterization of the first mutation causing a partial deletion in the FV molecule, resulting in a severe impairment of protein secretion.

Rare coagulation deficiencies

Deficiencies of coagulation factors (other than factor VIII and factor IX) that cause a bleeding disorder are inherited as autosomal recessive traits and are generally rare, with prevalences in the general population varying between 1 : 500 000 and 1 : 2 000 000. In the last few years, the number of patients with recessively transmitted coagulation deficiencies has increased in European countries with a high rate of immigration of Islamic populations, because in these populations, consanguineous marriages are frequent. Owing to the relative 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 haemophilia A and B. This article reviews these disorders in terms of their clinical manifestations and characterization of the molecular defects involved. The general principles of management are also discussed.

KEYWORDS

afibrinogenaemia, autosomal recessive disorders, factor VIII, factor XI, factor XIII.

Characterization of the genomic structure of the human neuronal nicotinic acetylcholine receptor CHRNA5/A3/B4 gene cluster and identification of novel intragenic polymorphisms

Genes coding for the alpha5, alpha3, and beta4 subunits (CHRNA5, CHRNA3, and CHRNB4) of the neuronal nicotinic acetylcholine receptors (nAChRs) are clustered on chromosome 15q24. Linkage of this chromosomal region to autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), an idiopathic partial epilepsy, was reported in one family. Moreover, mutations in other neuronal nAChR subunit genes coding for the alpha4 (CHRNA4) and the beta2 (CHRNB2) subunits were associated with ADNFLE. Apart from the exon-intron structure of CHRNA3, the genomic organization of this gene cluster was unknown, making comprehensive mutational analyses impossible. The genomic structure of CHRNA5 and CHRNB4 is here reported. Moreover, two hitherto unknown introns were identified within the 3' untranslated region of CHRNA3, causing a partial tail-to-tail overlap with CHRNA5. Four novel intragenic polymorphisms were identified and characterized in the cluster.

Congenital afibrinogenemia: mutations leading to premature termination codons in fibrinogen A alpha-chain gene are not associated with the decay of the mutant mRNAs

Congenital afibrinogenemia is a rare coagulation disorder with autosomal recessive inheritance, characterized by the complete absence or extremely reduced levels of fibrinogen in patients' plasma and platelets. Eight afibrinogenemic probands, with very low plasma levels of immunoreactive fibrinogen were studied. Sequencing of the fibrinogen gene cluster of each proband disclosed 4 novel point mutations (1914C>G, 1193G>T, 1215delT, and 3075C>T) and 1 already reported (3192C>T). All mutations, localized within the first 4 exons of the A alpha-chain gene, were null mutations predicted to produce severely truncated A alpha-chains because of the presence of premature termination codons. Since premature termination codons are frequently known to affect the metabolism of the corresponding messenger RNAs (mRNAs), the degree of stability of each mutant mRNA was investigated. Cotransfection experiments with plasmids expressing the wild type and each of the mutant A alpha-chains, followed by RNA extraction and semiquantitative reverse-transcriptase-polymerase chain reaction analysis, demonstrated that all the identified null mutations escaped nonsense-mediated mRNA decay. Moreover, ex vivo analysis at the protein level demonstrated that the presence of each mutation was sufficient to abolish fibrinogen secretion.

Coexistence of a novel homozygous nonsense mutation in exon 13 of the factor V gene with the homozygous Leiden mutation in two unrelated patients with severe factor V deficiency

A novel homozygous 3571C-->T nonsense mutation predicting the synthesis of a truncated factor V (FV) molecule was identified in exon 13 of the human coagulation factor V gene in two unrelated Italian probands with undetectable plasma levels of FV antigen and activity. Both patients were also homozygous for the FV Leiden mutation. Reverse transcription polymerase chain reaction studies showed strongly reduced mRNA levels of the mutant FV allele and FV heavy and light chains were not measurable in the plasma of the probands and reverse transcriptase. Haplotype analysis indicated that the nonsense mutation in both families had a common founder a long time ago.

Identification of four novel polymorphisms in the Aalpha and gamma fibrinogen genes and analysis of association with plasma levels of the protein

Four novel polymorphisms were identified in the fibrinogen gene cluster. Three of them were localized in the promoter regions of the Aalpha-chain (alpha -128 C/G, alpha -58 G/A) or the gamma-chain (gamma -239 A/G) gene, while the remaining one was identified in intron 9 of the gamma-chain gene (gamma 7792 C/T). Genotype distributions for these polymorphisms were analyzed in 200 healthy Italian individuals and were in Hardy-Weinberg equilibrium. Since high levels of plasma fibrinogen have been associated with an increased risk of cardiovascular disease and genetic variations have been evaluated as thrombotic risk predictors, we analyzed their role in determining the plasma levels of this protein. Owing to the low frequency of the rare allele of alpha -128 C/G and gamma -239 A/G polymorphisms, association with plasma fibrinogen levels was investigated for only alpha -58 G/A and gamma 7792 C/T. We also investigated in the same population two previously identified polymorphisms in the fibrinogen gene cluster (alpha TaqI and beta -455 G/A) chosen for their widely studied association with plasma fibrinogen levels. In the multivariate linear regression analysis, no statistically significant association with plasma fibrinogen levels was found.

A novel two base pair deletion in the factor V gene associated with severe factor V deficiency

We studied a family in which the proband, a 13-year-old boy, had unmeasurable plasma levels of coagulation factor V antigen and activity. Clinical symptoms were severe, with several episodes of haemorrhages in the mucosal tracts (gastrointestinal, nose and urinary) and recurrent haemarthroses that caused permanent arthropathy. Sequence analysis of the factor V gene demonstrated the presence of a novel 2 base pair (bp) homozygous deletion in exon 13 at positions 2833-2834. This mutation, present in the heterozygous state in the asymptomatic mother and absent in the healthy brother, introduced a frameshift and a premature stop at codon 900. This would predict the synthesis of a truncated factor V molecule, lacking part of the B domain and the complete light chain. Because of the existence of a surveillance mechanism that selectively recognizes and degrades mRNA molecules carrying premature termination codons, we analysed the relative abundance of mutant vs. wild-type mRNA molecules in the platelets of the heterozygous proband's mother. The mutant mRNA was significantly reduced in amount (mutant/wild-type ratio 0.35). This is the first reported mutation in the factor V gene causing severe factor V deficiency, the effect of which was quantitatively analysed at mRNA level.

A new biallelic polymorphism in intron 1 of the CHRNA4 gene may cause erroneous genotyping of a closely linked CA repeat marker

A new polymorphism in intron 1 of the neuronal nicotinic acetylcholine receptor alpha 4 subunit gene (CHRNA4) was identified. It consists of a G to T substitution located in the downstream flanking region of a previously reported CA repeat marker. This polymorphism whose frequency is about six percent in a control population occurs near the 3' end of the reverse primer generally used to type the CA repeat marker. Data are presented showing that the newly identified polymorphism causes erroneous genotyping of the CA repeat marker which can alter the results of linkage analysis for CHRNA4. The use of a different reverse primer located 34 nt downstream of the published sequence overcame errors in genotyping and identified two novel alleles of the CA repeat marker. Re-typing of the marker with the new proposed primer pair in a Caucasian control population of 107 unrelated individuals was also performed

Afibrinogenemia: first identification of a splicing mutation in the fibrinogen gamma chain gene leading to a major gamma chain truncation

Congenital afibrinogenemia is a rare autosomal recessive disorder characterized by the complete absence of plasma fibrinogen and by a bleeding tendency ranging from mild to moderately severe. Beside a deletion of the almost entire Aalpha-chain gene, only 2 missense mutations in the C-terminal domain of the Bbeta-chain have been very recently described as being associated with afibrinogenemia. We studied a Pakistani patient with unmeasurable plasma levels of functional and immunoreactive fibrinogen. Sequencing of the fibrinogen genes revealed a homozygous G-->A transition at position +5 of intron 1 of the gamma-chain gene. The predicted mutant fibrinogen gamma-chain would contain the signal peptide, followed by a short stretch of aberrant amino acids, preceding a premature stop codon. To demonstrate the causal role of the identified mutation, we prepared expression vectors containing a region of the fibrinogen gamma-chain gene spanning from exon 1 to intron 4 and carrying either a G or an A at position +5 of intron 1. Transient transfection of the mutated plasmid in HeLa cells, followed by RNA extraction and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, allowed us to demonstrate the production of an erroneously spliced messenger RNA (mRNA), retaining intron 1, as shown by direct sequencing. A normal splicing occurred in HeLa cells transfected with the wild-type plasmid. This is the first report of a mutation in the fibrinogen gamma-chain gene causing afibrinogenemia and indicates that, in addition to the Aalpha and Bbeta-chain genes, the gamma-chain gene must also be considered in mutation screening for afibrinogenemia.

Refined mapping of CHRNA3/A5/B4 gene cluster and its implications in ADNFLE

The chromosome 15q24 region, containing the CHRNA3/A5/B4 gene cluster, coding for the alpha3, alpha5 and beta4 subunits of neuronal nicotinic acetylcholine receptors, has been reported to be linked to autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) in one family. However, nor the gene nor the mutation involved have been identified. We report the refined mapping of CHRNA3/A5/B4 cluster. Segregation analyses of CHRNA3/A5/B4 polymorphisms in families showing recombinations for 15q24 G¿en¿ethon STR markers allowed to position the cluster in a 0.6 cM interval, between STRs D15S1027 and D15S1005. This location is external to the 15q24-ADNFLE-linked region, therefore excluding the involvement of this cluster in the pathogenesis of ADNFLE in the 15q24-linked family. Moreover, these data provide more precise information for further linkage studies.

cDNA cloning of turtle prion protein

Cloning of the cDNA coding for the 270-residue turtle prion protein is reported. It represents the most remote example thus far described. The entire coding region is comprised in a single exon, while a large intron interrupts the 5' UTR. The common structural features of the known prion proteins are all conserved in turtle PrP, whose identity degree to mammalian and avian proteins is about 40 and 58%, respectively. The most intriguing feature, unique to the turtle prion, is the presence of an EF-hand Ca(2+) binding motif in the C-terminal half of the protein.

The intron-containing L3 ribosomal protein gene (RPL3): sequence analysis and identification of U43 and of two novel intronic small nucleolar RNAs

Isolation and sequencing of bovine and human intron-containing L3 ribosomal protein genes are here reported. They exhibit very similar organisation, both comprising 10 exons and nine introns. A polymorphic locus, involving a 19-bp deletion, was found in intron 6 of the human gene. The frequency of the two alleles has been estimated in 200 haploid genomes. In bovine and human genes intron sequences are rather different, except for limited regions, located in corresponding positions, which show a surprisingly high degree of identity. All these regions contain conserved features defining the box C/D class of small nucleolar RNAs. Demonstration is given that U43 small nucleolar RNA is encoded within the first intron of both bovine and human genes. Single nucleotide sequences, encoding two novel species of small nucleolar RNAs (U82, U83a and U83b), are located in introns 3, 5 and 7. Their expression has been investigated and a possible role of these molecules in 2'-O-ribose methylation of rRNAs is discussed.

Missense mutations in the human beta fibrinogen gene cause congenital afibrinogenemia by impairing fibrinogen secretion

Congenital afibrinogenemia is a rare autosomal recessive disorder characterized by bleeding that varies from mild to severe and by complete absence or extremely low levels of plasma and platelet fibrinogen. Although several mutations in the fibrinogen genes associated with dysfibrinogenemia and hypofibrinogenemia have been described, the genetic defects of congenital afibrinogenemia are largely unknown, except for a recently reported 11-kb deletion of the fibrinogen Aalpha-chain gene. Nevertheless, mutation mechanisms other than the deletion of a fibrinogen gene are likely to exist because patients with afibrinogenemia showing no gross alteration within the fibrinogen cluster have been reported. We tested this hypothesis by studying the affected members of two families, one Italian and one Iranian, who had no evidence of large deletions in the fibrinogen genes. Sequencing of the fibrinogen genes in the 2 probands detected 2 different homozygous missense mutations in exons 7 and 8 of the Bbeta-chain gene, leading to amino acid substitutions Leu353Arg and Gly400Asp, respectively. Transient transfection experiments with plasmids expressing wild-type and mutant fibrinogens demonstrated that the presence of either mutation was sufficient to abolish fibrinogen secretion. These findings demonstrated that missense mutations in the Bbeta fibrinogen gene could cause congenital afibrinogenemia by impairing fibrinogen secretion. (Blood. 2000;95:1336-1341)

Genomic organization of the human gamma adducin gene

We report the genomic structure of the human gamma adducin gene (ADD3). Adducin is a protein involved in cytoskeletal assembly and composed of alpha-beta or alpha-gamma subunits which share a high degree of homology between human and rat. Mutations in alpha subunit have been shown associated to both human and rat hypertension. The human ADD3 gene spans over 20 kb and is composed of at least 13 introns and 14 exons covering the entire coding region. The exon size ranges from 81 bp to greater than 293 bp and the intron size from 111 bp to longer than 3.2 kb. We also demonstrate the presence of an alternative splicing event around exon 13, whose sequence, position, and expression is analogous in rat Add3 gene. Moreover, human ADD3 amino acid sequence presents 91.9% of identity compared to rat sequence. Characterization of human ADD3 gene provides an important tool for mutation analysis.

SER252PHE and 776INS3 mutations in the CHRNA4 gene are rare in the Italian ADNFLE population

41 patients (19 sporadic and 22 familial) affected by autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) were analyzed for the presence of two mutations (Ser252Phe, 776ins3) in the CHRNA4 gene, reported to be associated with this disease. Electroclinical findings of sporadic forms were indistinguishable from familial ones. In none of the patients, these mutations were found by dot blot analysis with allele specific oligonucleotides. These data, obtained on the largest group so far studied, suggest the rarity of the reported mutations.

A new exon in the 5' untranslated region of the connexin32 gene

The cloning and sequencing of two bovine connexin32 cDNAs are reported. Comparative analysis with known corresponding mammalian cDNA and protein sequences, besides confirming a high degree of similarity among these proteins, allowed us to identify some specific features of the bovine connexin32 gene. The latter include: the presence of a novel exon in the 5' UTR which is alternatively spliced, giving rise to a new mRNA species; the presence of two potential hairpin loops in the 5' and 3' UTR; and the presence of an additional amino acid, glycine235, in the C-terminal domain of the 284 residue protein. Among the common features, the presence of polypyrimidine clusters within the 3' UTR, containing a consensus sequence for a cis-acting element, is noteworthy. Expression of connexin32 mRNAs was analysed in 16 bovine tissues. Transcript analysis suggests the presence, in cattle, of an alternative downstream promoter.

Analysis of the 16S rRNA gene sequence of the coryneform bacterium associated with hyperkeratotic dermatitis of athymic nude mice and development of a PCR-based detection assay

By 16S rDNA sequencing the authors have characterized the coryneform bacteria associated with hyperkeratotic dermatitis (HD) of athymic nude mice isolated from six different outbreaks of the disease in Northern Italy. This analysis has allowed the authors to confirm the classification of the bacteria as Corynebacterium bovis and to develop a 16S rDNA-based polymerase chain reaction (PCR) detection assay. The test was performed directly on the DNA extracted from epidermal swabs. The PCR primers were chosen to match the 16S rDNA sequence fragments which differ most from the other Corynebacterium spp. The test was shown to be both sensitive and specific for C. bovis. Detection of as few as three viable bacterial cells was possible with the use of an oligonucleotide probe in a liquid hybridization assay.

Identification of a glucocorticoid response element in the human gamma chain fibrinogen promoter

The effect of the synthetic glucocorticoid hormone dexamethasone on human gamma chain fibrinogen gene expression was examined. The whole promoter region of 3.8 kb of this gene and progressive 5'-deletions were inserted into a promoterless expression vector, upstream of the luciferase gene and transiently transfected into the human hepatoma HepG2 cells, in the presence or in the absence of dexamethasone stimulation. Deletion analysis allowed to identify a region located between -1359 and -954 bp upstream from the transcription start site, involved in hormone inducibility. On the basis of a computer-assisted analysis, a putative GRE was found in this region at bases -1116 to -1102. Specific point mutations eliminating this putative GRE led to complete loss of glucocorticoid inducibility, thus indicating its functional role. Binding of the rat glucocorticoid receptor to this site was demonstrated by mobility-shift assays.

Identification and spatial distribution of the mRNA encoding the gp49 component of the gilthead sea bream, Sparus aurata, egg envelope

A cDNA encoding the precursor of one of the major components of gilthead sea bream, Sparus aurata, egg envelope has been cloned by reverse transcriptase polymerase chain reaction (RT-PCR) techniques. The clone was isolated starting from total RNA extracted from the liver of spawning female fish and estradiol-17 beta-treated male fish. Sequence analysis revealed that the cDNA encoded a protein of 405 aa corresponding to 49-kDa component (termed gp49), a glycoprotein belonging to the N-linked type. The gp49 protein is homologous to the Zl-3 of medaka Oryzias latipes, the mammalian ZPC and ZPC homologues of Xenopus laevis (xlZPC) and carp Cyprinus carpio (ccZPC). In addition, the open reading frame also encodes an additional aa sequence, the signal peptide, located in the N-terminal region of the protein. RT-PCR and in situ expression analyses evidenced an organ-restricted pattern: the mRNA was detected only in liver of spawning female and estradiol-17 beta-treated male fish but not in other tissues.

cDNA cloning and expression of the flavoprotein D-aspartate oxidase from bovine kidney cortex

The isolation and sequencing of the complete cDNA coding for a d-aspartate oxidase, as well as the overexpression of the recombinant active enzyme, are reported for the first time. This 2022 bp cDNA, beside the coding portion, comprises a 5' untranslated tract and the whole 3' region including the polyadenylation signal and the poly(A) tail. The encoded protein comprises 341 amino acids, with the last three residues (-Ser-Lys-Leu) representing a peroxisomal targeting signal 1 (PTS1), hitherto unknown for this protein. The overexpression of recombinant d-aspartate oxidase was achieved in a prokaryotic system, and a soluble and active enzyme was obtained which accounted for about 10% of total bacterial protein. Comparisons with the known cDNAs for mammalian d-amino acid oxidase, another peroxisomal enzyme, are also made. The close structural and functional similarities shared by these enzymes at the protein level are not reflected at the nucleic acid level.

L-aspartate oxidase from Escherichia coli. I. Characterization of coenzyme binding and product inhibition

This paper reports the biochemical characterization of the flavoprotein L-aspartate oxidase from Escherichia coli. Modification of a previously published procedure allowed overexpression of the holoenzyme in an unproteolysed form. L-Aspartate oxidase is a monomer of 60 kDa containing 1 mol of noncovalently bound FAD/mol protein. A polarographic and two spectrophotometric coupled assays have been set up to monitor the enzymatic activity continuously. L-Aspartate oxidase was subjected to product inhibition since iminoaspartate, which results from the oxidation of L-aspartate, binds to the enzyme with a dissociation constant (Kd) equal to 1.4 microM. The enzyme binds FAD by a simple second-order process with Kd 0.67 microM. Site-directed mutagenesis of the residues E43, G44, S45, F47 and Y48 located in the putative binding site of the isoallossazinic portion of FAD reduces the affinity for the coenzyme.