Amino Acid Dimorphism Research Articles

Homozygosity for killer immunoglobin-like receptor haplotype A predicts complete molecular response to treatment with tyrosine kinase inhibitors in chronic myeloid leukemia patients

Several recent reports suggest a possible role for killer immunoglobulin-like receptors (KIR) in the onset of chronic myeloid leukemia (CML) and response to therapy with tyrosine kinase inhibitors (TKIs). To explore this hypothesis, we studied KIRs and their human leukocyte antigen class I ligands in 59 consecutive patients with chronic-phase CML (mean age, 53 years; range, 23-81 years) and a group of 121 healthy control participants belonging to the same ethnic group as the patients. The 2-year cumulative incidence of complete molecular response, obtained after a median of 27 months (range, 4-52 months), was 51.2%. An increased frequency of the activating receptor KIR2DS1 (pm = 0.05) and a reduced frequency of the KIR-ligand combination KIR2DS2/2DL2 absent/C1 present (pm = 0.001) were significantly associated with CML. Moreover, KIR repertoires in patients appeared to influence response to TKI therapy. Homozygosity for KIR haplotype A (pm = 0.01), a decreased frequency of the inhibitory KIR gene KIR2DL2 (pm = 0.02), and low numbers of inhibitory KIR genes (pm = 0.05) were all significantly associated with achievement of complete molecular remission. These data suggest that a decrease in properly stimulated and activated NK cells might contribute to the occurrence of CML and indicate homozygosity for KIR haplotype A as a promising immunogenetic marker of complete molecular response that could help clinicians decide whether to withdraw treatment in patients with CML.

Association between Platelet Glycoprotein Ib‐α and Myocardial Infarction

Myocardial infarction (AMI) is a complex multifactorial disorder. Platelet adhesion and thrombosis are pivotal events in the development of atherosclerotic lesions. Occlusive thrombus is almost exclusively initiated by plaque rupture and adhesion of platelets to subendothelial von Willebrand factor (vWf) by its specific platelet receptor, the alpha-chain of glycoprotein (GP) Ib-IX-V complex of the human platelet-specific antigens (HPA). Two polymorphisms have been reported in the sequence of GPIb-alpha. The first, a C/T transition at nucleotide 1018 results in an amino acid dimorphism (Thr/Met) at residue 145 of GPIb-alpha, which is located within the vWF-binding domain of the receptor. The second is a T/C polymorphism in the Kozak sequence at position -5 from the initiator ATG. This affects the receptor density on the platelet surface. We assessed 1018 C/T and -5 T/C Kozak polymorphisms to see whether they are associated with AMI in homogeneous populations of Sicilian patients with AMI. To this end, we have analyzed the distribution of 1018 C/T and -5 T/C Kozak polymorphisms in 105 young Sicilian patients (<46 years) and 110 healthy age-related controls, by PCR-SSP and PCR-RFLP. Our results demonstrate no significant differences in the frequency of 1018 C/T and -5 T/C Kozak polymorphism between patients with AMI and controls. Stratifying by gender, there is no difference between male and female patients and control data. Thus, our results indicate that the HPA-2 polymorphisms are not associated with an increased risk for AMI at early onset (< 46 years) both in men and in women.

Platelet glycoprotein I(b)alpha and integrin alpha2 beta1 polymorphisms: gene frequencies and linkage disequilibrium in a population diversity panel.

Genetic variants in the GP1BA and ITGA2 genes have been proposed as potential modifiers for arterial vascular disease and bleeding disorders. Since ancestry may play an important role in the prevalence of these variants, we sought to determine their allele frequency and linkage disequilibrium in a collection of 1064 DNA samples from 51 ethnic groups. We studied haplotypes of ITGA2 defined by single nucleotide substitutions at positions -52, 807, and 1648, and GP1BA variants defined by sequence changes in positions -5 (Kozak), 1018 (T145M, HPA-2) and 1285 (VNTR A, B, C and D). Frequency of haplotypes of ITGA2 showed considerable variation across the different groups, with a higher prevalence of the haplotype -52C or T/807C/1648A observed in African compared with caucasian and Asian populations. The haplotypes 52C/807T/1648A and -52T/807T/1648A were not observed in caucasians or South Americans. While relative frequencies of the GP1BA Kozak alleles were comparable across groups, the methionine allele (HPA-2b) showed a higher frequency in Africa (0.26) than in the other groups. We also observed a high prevalence of the VNTR B allele in the African and Israeli populations. Haplotype analysis revealed incomplete linkage disequilibrium between the HPA-2 and VNTR alleles. Incorporation of GP1BA variants into the set of SNPs already genotyped by the HapMap project disrupted the pre-existing haplotype block. These data provide a valuable resource for optimal selection of variants best tailored for association studies of vascular disease or bleeding disorders when examining individuals of different ancestral origins.

Amino acid dimorphism and parasite immune evasion: cellular immune responses to a promiscuous epitope of Plasmodium falciparum merozoite surface protein 1 displaying dimorphic amino acid polymorphism are highly constrained.

Like most other surface-exposed antigens of Plasmodium falciparum, the leading malaria vaccine candidate merozoite surface protein (MSP)-1 contains a large number of dimorphic amino acid positions. This type of diversity is presumed to be associated with parasite immune evasion and represents one major obstacle to malaria subunit vaccine development. To understand the precise role of antigen dimorphism in immune evasion, we have analyzed the flexibility of CD4 T cell immune responses against a semi-conserved sequence stretch of the N-terminal block of MSP-1. While this sequence contains overlapping promiscuous T cell epitopes and is a target for growth inhibitory antibodies, three dimorphic amino acid positions may limit its suitability as component of a multi-epitope malaria vaccine. We have analyzed the CD4 T cell responses in a group of human volunteers immunized with a synthetic malaria peptide vaccine containing a single MSP-143-53 sequence variant. All human T cell lines and HLA-DR- or -DP-restricted T cell clones studied were exclusively specific for the sequence variant used for immunization. Competition peptide binding assays with affinity-purified HLA-DR molecules indicated that dimorphism does not primarily affect HLA binding. Modeling studies of the dominant restricting HLA-DRB1*0801 molecule showed that the dimorphic amino acids represent potential TCR contact residues. Lack of productive triggering of the TCR by MHC/variant peptide ligand complexes thus seems to be the characteristic feature of parasite immune evasion associated with antigen dimorphism.

The effect of a common methylenetetrahydrofolate reductase mutation on levels of homocysteine, folate, vitamin B12 and on the risk of premature atherosclerosis

An increased total plasma homocysteine level is an established risk factor for atherosclerotic vascular disease. The plasma level of homocysteine is influenced by both environmental and genetic factors. An important genetic determinant of plasma homocysteine is a common amino acid dimorphism (Ala222Val) in the methylenetetrahydrofolate reductase (MTHFR) gene. Individuals homozygous for the Val allele have significantly higher homocysteine levels than those with an Ala/Val or Ala/Ala genotype. Moreover, the Val/Val genotype has been claimed to be a strong genetic risk factor for atherosclerosis. The aim of the present study is: (1) to determine the risk associated with the MTHFR dimorphism by comparing the genotype distribution in patients with premature atherosclerosis with that in a group of healthy controls; and (2) to investigate the relationship between the MTHFR genotype and parameters of homocysteine metabolism. The patient group consisted of 257 consecutive referred individuals with angiographically proven premature (<50 years of age) arterial disease (coronary, and/or peripheral vascular disease). A total of 272 healthy hospital workers without a history of vascular disease were selected as a control group. The MTHFR-genotype was determined by PCR and gel-electrophoresis. A methionine-loading test was performed on 245 patients, and, in addition to homocysteine, levels of folate and vitamin B12 were measured. We found a strong correlation between MTHFR genotype and plasma homocysteine levels both before and after methionine loading. In addition, the MTHFR genotype seems important for the inverse relationship between homocysteine and folate and vitamin B12 levels. Lastly, the MTHFR genotype distribution was not different between patient and control groups. MTHFR genotype is a strong determinant of plasma homocysteine levels. Moreover, the plasma level of folate, which by itself influences homocysteine levels, is also dependent on the MTHFR genotype. In Val/Val genotypes, low levels of both folate and B12 lead to a relatively large increase in homocysteine levels. Nevertheless, the MTHFR genotype does not increase the risk for premature coronary artery disease.

Expression of the amino acid dimorphism in the small myelin-associated glycoprotein cytoplasmic domain in rat peripheral nerves during postnatal development

The myelin-associated glycoprotein (MAG) is one of the proteins expressed during the period of myelin formation and is believed to play a major role in the initiation of myelination. It exists as two differentially expressed isoforms, L- and S-MAG, that are generated by alternative mRNA splicing. A nucleotide dimorphism at the mRNA level resulting in an Arg/Pro dimorphism in the cytoplasmic tail of the S-MAG protein has previously been detected in the rat brain. In this study, we show that this dimorphism is detectable in the rat peripheral nervous system. We propose an allelic origin for the dimorphism and demonstrate the differential expression of the S-MAG alleles in the sciatic nerves of heterozygous rats during the period of active myelination. We also present data on the properties of the two S-MAG cytoplasmic domains produced as GST fusion proteins. The importance of this differentially expressed amino acid dimorphism is discussed, taking into account both its probable effect on the S-MAG cytoplasmic domain function and its significance in functional and structural studies concerning the S-MAG protein.

HFE codon 63/282 (H63D/C282Y) dimorphism in German patients with genetic hemochromatosis.

Genetic hemochromatosis (GH) is closely associated with genes of the major histocompatibility complex (MHC) on chromosome 6. Recently, a candidate gene for GH, with structural similarities to MHC class I genes, designated HLA-H and presently named HFE, has been cloned. The HFE gene is localized telomeric to the MHC and several reports have indicated that the HFE gene is mutated in GH patients. In the present study we have analyzed the relationship of HFE gene variants and disease manifestation in GH patients and family members. Fifty-seven patients with GH, 73 family members and 153 healthy blood donors were studied for the amino acid dimorphism at codon 63 (His63Asp=H63D) and codon 282 (Cys282Tyr= C282Y) of the HFE gene. The codon 63 and 282 dimorphism were defined by PCR amplification of genomic DNA samples and restriction enzyme digestion using RsaI/SnaBI for C282Y and BclI/MboI for H63D. Ferritin, transferrin serum levels and total iron-binding capacity were determined prior to therapeutic intervention. The Tyr-282 substitution occurred in 53 (93%) of patients compared with 8 (5.2%) of controls (OR=169, P<0.0001). Fifty-one (90%) patients were Tyr-282 homozygous. In contrast, the Asp-63 substitution was present in 5 (8.8%) of the patients compared with 34 (22%) of controls (OR=0.39, P=NS) with none of the patients being homozygous. In Tyr-282 homozygous GH patients serum ferritin levels, transferrin saturation, liver iron and liver iron index were elevated significantly compared to Tyr-282-negative patients, whereas no difference was observed between Tyr/Cys-282 heterozygous and Tyr-282-negative patients.

Frequency and functional relevance of genetic threonine145/methionine145 dimorphism in platelet glycoprotein Ib alpha in an Italian population.

Threonine145/methionine145 dimorphism in platelet glycoprotein (GP) Ib alpha defines the human platelet antigen (HPA)-2 system that has been implicated in refractoriness to HLA-matched platelet transfusion and in neonatal immune thrombocytopenic purpura. The occurrence of this amino acid dimorphism was investigated in 379 Italian blood donors by studying their genomic DNA. Two oligonucleotide primers, Ib alpha-3 (5'-GGACGTCTCCTTCAACCGGC-3') and Ib alpha-4 (5'-GCTTTGGTGGGGAACTTGAC-3'), were used in a polymerase chain reaction to generate a 591-base pair fragment that was digested with the restriction enzyme Acy I. To investigate whether this dimorphism is involved in the binding of von Willebrand factor (vWF) to GPlb, the binding of vWF to the GPlb/IX complex was measured in two Met145/Met145 and two Thr145/Thr145 subjects. The genotypic frequencies are 78.9% for Thr/Thr, 19.8% for Thr/Met), and 1.3% for Met/Met; the allelic frequencies are 88.8% for Thr145 and 11.2% for Met145. Estimates for binding of subunit molecules per platelet at saturation and inhibition constant in mol per L, respectively, follow. In the presence of ristocetin (0.5 mg/mL), they are 11,460 +/- 2,040 and 1.26 +/- 0.44 x 10(-8) for normals and 11,230 +/- 2,330 and 1.29 +/- 0.48 x 10(-8) for patients. In the presence of botrocetin (2.5 micrograms/mL), they are 64,260 +/- 7,760 and 2.99 +/- 0.96 x 10(-8) for normals and 65,770 +/- 11,570 and 2.47 +/- 0.22 x 10(-8) for patients. Platelet aggregation responses obtained using platelet-rich plasma from donors with Met145/Met145 or Thr145/Thr145 genotype were within normal limits. Genotypic and phenotypic frequencies in the HPA-2 system in this population are consistent with those reported among the white population. Furthermore, the HPA-2 system is not involved in the binding of vWF to GPlb.

128 Amino acid dimorphism of the small myelin-associated glycoprotein isoform in the peripheral nervous system

International Journal of Developmental NeuroscienceVolume 14, Issue S1 p. 81-81 Article 128 Amino acid dimorphism of the small myelin-associated glycoprotein isoform in the peripheral nervous system Petri Kursula, Petri KursulaSearch for more papers by this authorVeli-Pekka Lehto, Veli-Pekka LehtoSearch for more papers by this authorAnthony M. Heape, Anthony M. HeapeSearch for more papers by this author Petri Kursula, Petri KursulaSearch for more papers by this authorVeli-Pekka Lehto, Veli-Pekka LehtoSearch for more papers by this authorAnthony M. Heape, Anthony M. HeapeSearch for more papers by this author First published: July-August 1996 https://doi.org/10.1016/0736-5748(96)80318-2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, IssueS111th Biennial Meeting of the International Society for Developmental NeuroscienceJuly-August 1996Pages 81-81 RelatedInformation

Plasma factor VII levels are influenced by a polymorphism in the promoter region of the FVII gene.

Genetic factors play a role in determining the variability of plasma factor VII (FVII) levels in healthy individuals. There is also evidence that high serum lipids are associated with high FVII levels in plasma. In the promoter region of the human FVII a DNA polymorphism has been described, originating from a decanucleotide insert present in the less frequent allele. This biallelic system, reflecting the absence (AA) or presence (Aa) of the decanucleotide, can be detected by a DNA enzyme immunoassay of PCR products. We evaluated the association between the polymorphic alleles and the levels of FVII:Ag and FVII:C in 100 healthy individuals and in 19 hypertriglyceridemic individuals. Among healthy individuals, mean FVII:Ag and FVII:C levels of those with the homozygous genotype (A/A; mean FVII:Ag 112%, mean FVII:C 109%) were significantly higher (P < 0.001) than the mean levels of those with the heterozygous genotype (A/a, mean FVII:Ag 80%, mean FVII:C 90%; P < 0.001). Similar genotype-associated differences for FVII:Ag and FVII:C were found in individuals with triglycerides above 250 mg/dl (P < 0.05). FVII:C and FVII:Ag levels were positively related to triglycerides only in individuals without the insert (P < 0.01); there was no significant relationship in those carrying the allele with the insert (A/a; P = 0.43 and 0.08). Our findings of genotype-associated differences in FVII levels and interactions with triglycerides are similar to those obtained with the amino acid dimorphism at position 353 of the factor VII protein.

Amino acid dimorphism in IL1A is detectable by PCR amplification.

Amino acid dimorphism in IL1A is detectable by PCR amplification.

Genetic and Structural Characterization of an Amino Acid Dimorphism in Glycoprotein Iba Involved in Platelet Transfusion Refractoriness

AbstractThe platelet-specific alloantigen. Sib®, located within the a-subunit of the glycoprotein (GP) Ib-IX membrane receptor, has been found to be involved in the pathogenesis of platelet transfusion refractoriness. We have identified the existence of a naturally occurring threonine / methionine dimorphism at position 145 of the GPIbα sequence, and determined that the Sib® antigen corresponds to the molecule containing methi-onine145. The diallelic codons can be detected by restriction enzyme analysis of amplified genomic DNA fragments from the GPIbα gene. Evaluation of 61 healthy blood donors showed that the allele frequencies are 89% and 11% for the threonine145 and methionine145 codons, respectively. A posi-tive correlation exists between platelet reactivity with the anti-Sib® antibody and the presence of a methionine145-encoding allele. Moreover, recombinant expression of two soluble GPIbα fragments differing only at residue 145, provided definitive evidence that the human anti-Sib® antibody reacts only with the molecule containing methionine145. These results explain the structural basis of the Sib® human alloantigen system and define screening methodologies useful in transfusion medicine to match donor and recipient platelets accordingly.

Genetic and structural characterization of an amino acid dimorphism in glycoprotein Ib alpha involved in platelet transfusion refractoriness

The platelet-specific alloantigen, Siba, located within the alpha-subunit of the glycoprotein (GP) Ib-IX membrane receptor, has been found to be involved in the pathogenesis of platelet transfusion refractoriness. We have identified the existence of a naturally occurring threonine/methionine dimorphism at position 145 of the GPIb alpha sequence, and determined that the Siba antigen corresponds to the molecule containing methionine145. The diallelic codons can be detected by restriction enzyme analysis of amplified genomic DNA fragments from the GPIb alpha gene. Evaluation of 61 healthy blood donors showed that the allele frequencies are 89% and 11% for the threonine145 and methionine145 codons, respectively. A positive correlation exists between platelet reactivity with the anti-Siba antibody and the presence of a methionine145-encoding allele. Moreover, recombinant expression of two soluble GPIb alpha fragments differing only at residue 145, provided definitive evidence that the human anti-Siba antibody reacts only with the molecule containing methionine145. These results explain the structural basis of the Siba human alloantigen system and define screening methodologies useful in transfusion medicine to match donor and recipient platelets accordingly.