An additional HpaII polymorphism in exon 2 of the human platelet membrane glycoprotein IIIa gene

New mutation in the platelet beta3-integrin gene: implication for the diagnosis of fetomaternal alloimmunization

BACKGROUND

Fetal ventriculomegaly is a relatively common finding and fetomaternal alloimmune thrombocytopenia may be one of the causes.

STUDY DESIGN AND METHODS

Such a case discovered at 21 weeks of gestation leading to platelet (PLT) immunologic testing is reported here. PLT genotyping was performed by polymerase chain reaction (PCR)-sequence-specific primers (SSPs) method and PCR-restriction fragment length polymorphism (RFLP) analysis. Serologic investigation was done with the monoclonal antibody-specific immobilization of PLT antigens technique.

RESULTS

The mother was found to be HPA-1b homozygous and the father HPA-1a homozygous with PCR-SSP, but the mother was found to be HPA-1 heterozygous by phenotyping. This result was confirmed by PCR-RFLP. Sequencing of the glycoprotein IIIa exon 3 revealed a heterozygous mutation 262T > C, which does not induce an amino acid change. It is localized in the sequence of the antisense primer of the HPA-1 PCR-SSP, inducing the sole amplification of the DNA copy bearing the HPA-1b allele.

CONCLUSION

Even if such mutations are a rare event, PLT phenotyping is still of interest to avoid rare false PLT typing assignation, the unknown polymorphism being only discovered by such a combination of techniques.

HPA polymorphism in sub-Saharan African populations: Beninese, Cameroonians, Congolese, and Pygmies

The frequency of human platelet antigen-1 (HPA-1) to HPA-11w (excluding HPA-8w) and HPA-15 systems was studied in four sub-Saharan populations: Beninese, Congolese (Democratic Republic of Congo Kinshasa), Cameroonians, and Aka pygmies (Central African Republic). No report of HPA prevalence has previously been published concerning these populations which are characterized by the highest HPA-2b gene frequencies of any reported to date (Aka 0.393, Benin 0.292, Cameroon 0.237, and Congo 0.224) and at lesser degree HPA-5b (Aka 0.405, Congo 0.268, Cameroon 0.254, and Benin 0.182). This study is of great importance (i) particularly in the context of the diversity caused by the population migrations, we may observe today in our hospitals (ii) to confirm that the Pygmy population with distinctive frequencies (absence of the HPA-1b, HPA-2b, and HPA-5b highest frequencies) is an isolated population.

Eleven human platelet systems studied in the Vietnamese and Ma'ohis Polynesian populations

The frequencies of human platelet antigens (HPA) are variable among different ethnic groups. Platelet phenotyping and genotyping in different populations are important to the clinical implications of antiplatelet alloimmunization. No report on HPA prevalence has been published concerning the Vietnamese Kinh and Ma'ohis Polynesian populations. Recent anthropological and genetic marker studies suggest that these two groups have a common origin in East Asia, so we have conducted a combined study concerning the frequency of HPA-1 to HPA-11w systems (excluding HPA-8w) and Gov in these two populations. The results demonstrate a similar pattern of prevalence between Ma'ohis and most of the Asian populations. However, it should be noted that the frequency of HPA-2 is closer to northern Caucasian frequencies than to Asian frequencies. The population of Kinh shows an HPA distribution that is closer to the Chinese population than to the northeastern Thais except for HPA-3, closer to the Indonesian population. Given HPA-3 gene frequency distribution fetomaternal incompatibility could occur more frequently with the risk of alloantibody production.

Human platelet antigen 1 (HPA 1) genotyping with 5' nuclease assay and sequence-specific primers reveals a single nucleotide deletion in intron 2 of the HPA 1a allele of platelet glycoprotein IIIa

We have established a 5' nuclease assay (5' NA) for human platelet antigen (HPA) 1a/b allelic discrimination. The assay is based on the simultaneous amplification and detection of the two targets in a one-tube system. The results are read optically, immediately after termination of the polymerase chain reaction (PCR), and no post-PCR processing is necessary. This genotyping procedure is less time-consuming and cheaper than our conventional sequence-specific primer PCR (SSP-PCR), which is run as a two-tube test, with verification of the results after electrophoresis in agarose gel. The reduction of analytical steps, simplification of the procedure and potential for automation were important advantages for our choice of system. This test system is more suitable for large-scale testing and fits better for our screening programme for HPA 1bb determination. DNA from 1093 individuals were tested in parallel with the SSP-PCR and the 5' NA. One thousand and ninety-one samples gave identical results in SSP-PCR and 5' NA. Upon repeated testing, two samples consistently came out as HPA 1bb in SSP-PCR and HPA 1ab in 5' NA. DNA sequencing revealed a defect located in an intronic area that corresponds to the consensus primer used for the SSP-PCR HPA 1a typing.

Gene frequencies of human platelet antigens in the Tunisian population

Gene frequencies for the human platelet antigens HPA-1, -3 and -5 in the Tunisian population were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) on 93 volunteer blood donors (78 were tested for HPA-1, 90 for HPA-3 and 93 for HPA-5). This study shows the highest frequencies of the HPA-1b (0.25) and HPA-5b (0.22) yet recorded. These antigens are considered as markers of a high risk of platelet alloimmunisation in other populations, and for this reason particular attention should be paid in the case of pregnancy or blood transfusion in this population. The 9 base pair deletion located in intron 21 of the GPIIb gene associated with HPA-3b determinant is present in this population. No individual showed the polymorphism associated with HPA-1b (T-->G at codon 40 of the GPIIIa).

R to Q Amino Acid Substitution in the GFFKR Sequence of the Cytoplasmic Domain of the Integrin IIb Subunit in a Patient With a Glanzmann’s Thrombasthenia-Like Syndrome

The integrin IIbβ3 mediates platelet aggregation through its fibrinogen and adhesive protein-binding properties. Particular interest concerns the role of the cytoplasmic domains of IIb and β3. We now report the molecular analysis of IIbβ3 from a patient with a Glanzmann’s thrombasthenia-like syndrome for whom the principal characteristics are an approximate 50% total platelet content of IIbβ3 but with a much lower proportion in the surface pool (Hardisty et al, Blood 80:696, 1992). Polymerase chain reaction (PCR) single-strand conformational polymorphism and DNA sequencing showed a heterozygous mutation giving rise to amino acid substitution R995 to Q in the GFFKR sequence of the cytoplasmic domain of IIb. Reverse transcriptase-PCR and polymorphism analysis only detected mRNA for the mutated allele of the IIb gene and a single allele of the β3 gene in his platelets, suggesting other unidentified defects. Site-directed mutagenesis followed by transient expression of the mutated IIb together with wild-type β3 in Cos-7 cells resulted in a markedly decreased expression of the complex at the cell surface when compared with cells transfected with wild-type IIb and β3. Flow cytometry with PAC-1 and a stable Chinese hamster ovary–transfected cell line showed that the mutated receptor was not locked into a high activation state, although it became so in the presence of the activating antibody, anti-LIBS6. This is the first reported natural mutation in the highly conserved GFFKR sequence of the IIb cytoplasmic domain.

R to Q Amino Acid Substitution in the GFFKR Sequence of the Cytoplasmic Domain of the Integrin IIb Subunit in a Patient With a Glanzmann’s Thrombasthenia-Like Syndrome

The integrin IIbβ3 mediates platelet aggregation through its fibrinogen and adhesive protein-binding properties. Particular interest concerns the role of the cytoplasmic domains of IIb and β3. We now report the molecular analysis of IIbβ3 from a patient with a Glanzmann’s thrombasthenia-like syndrome for whom the principal characteristics are an approximate 50% total platelet content of IIbβ3 but with a much lower proportion in the surface pool (Hardisty et al, Blood 80:696, 1992). Polymerase chain reaction (PCR) single-strand conformational polymorphism and DNA sequencing showed a heterozygous mutation giving rise to amino acid substitution R995 to Q in the GFFKR sequence of the cytoplasmic domain of IIb. Reverse transcriptase-PCR and polymorphism analysis only detected mRNA for the mutated allele of the IIb gene and a single allele of the β3 gene in his platelets, suggesting other unidentified defects. Site-directed mutagenesis followed by transient expression of the mutated IIb together with wild-type β3 in Cos-7 cells resulted in a markedly decreased expression of the complex at the cell surface when compared with cells transfected with wild-type IIb and β3. Flow cytometry with PAC-1 and a stable Chinese hamster ovary–transfected cell line showed that the mutated receptor was not locked into a high activation state, although it became so in the presence of the activating antibody, anti-LIBS6. This is the first reported natural mutation in the highly conserved GFFKR sequence of the IIb cytoplasmic domain.

HPA-10wb (Laa): Genetic Determination of a New Platelet-Specific Alloantigen on Glycoprotein IIIa and Its Expression in COS-7 Cells

The heterodimeric complex glycoprotein (GP)IIb-IIIa, the fibrinogen receptor of platelets, carries numerous alloantigen systems. These polymorphisms are responsible for the immune response after transfusion or during pregnancy. In the latter case, the mother develops an antibody against an epitope present on fetal platelets, and this results in platelet destruction in the fetus. In this report, we describe the molecular characterization of a new alloantigen (Laa) on GPIIIa responsible for neonatal alloimmune thrombocytopenia (NAIT). Using polymerase chain reaction (PCR)–singlestrand conformation polymorphism (SSCP) and DNA sequencing, we found a point mutation (G to A) in a heterozygous state on the GPIIIa gene leading to amino acid substitution Arg to Gln at position 62 of the mature protein. Transient expression of GPIIb-IIIa complexes in Cos-7 cells using wild-type or mutated GPIIIa cDNA allowed us to demonstrate that this mutation was responsible for expression of the Laa epitope.

A rapid genotype assay for Pla haplotypes

The method described here results in simple visual analysis of 1, 2, or 3 ethidium bromide-stained bands corresponding to the PlA1, PlA2 or PlA1/A2 phenotypes, respectively. The amplification primers, designed to yield a 711bp product which encompasses exon 2 and substantial intronic sequence both 5' and 3' of the exon enable exquisite resolution of the restriction enzyme digestion products which define the alleles. In addition to prediction of fetal risk of neonatal alloimmune thrombocytopenia using this method, an ethnically heterogeneous pool of platelet donors was screened for the platelet antigen PlA (HPA-1) and gave unequivocal results which should be useful for platelet matching.

Bilateral linkage between a new deletion polymorphism in intron 21 of the GP IIb gene and the HPA-3b (Bakb) determinant

Glycoproteins (GP) IIb (alpha IIb) and GP IIIa (beta 3) form heterodimeric complexes (GP IIb-IIIa) at the platelet surface and mediate platelet aggregation by binding fibrinogen after platelet activation. The structures and DNA sequences of the GP IIb and GP IIIa genes are known. Punctual mutations resulting in alloantigen systems (HPA) have been described on both genes, as have a series of genetic defects giving rise to Glanzmann's thrombasthenia (GT). We now report a nine base pair deletion located in intron 21 of the GP IIb gene. This was found both in unrelated GT patients and in normal individuals. Subsequent studies showed that the deletion polymorphism and the mutation responsible for the platelet alloantigen. HPA-3b, were linked together. The deletion was always present when the gene carried the HPA-3b genotype, but was never observed in association with the HPA-3a polymorphism. Analysis of 60 independent alleles from 30 unrelated caucasian individuals revealed no exceptions to this linkage. It is the first time that two genetic markers have been reported to be linked to each other on the GP IIb gene.