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

Molecular typing of human platelet and neutrophil antigens (HPA and HNA)

Genotyping is an important tool in the diagnosis of disorders involving allo-immunisation to antigens present on the membranes of platelets and neutrophils. To date 28 human platelet antigens (HPAs) have been indentified on six polymorphic glycoproteins on the surface of platelets. Antibodies against HPAs play a role in foetal and neonatal alloimmune thrombocytopenia (FNAIT), post-transfusion purpura (PTP) and refractoriness to donor platelets. The 11 human neutrophil antigens (HNAs) described to date have been indentified on five polymorphic proteins on the surface of granulocytes. Antibodies to HNAs are implicated with foetal and neonatal alloimmune neutropenia (FNAIN), autoimmune neutropenia (AIN) and transfusion related acute lung injury (TRALI). In this report, we will review the molecular basis and techniques currently available for the genotyping of human platelet and neutrophil antigens.

Human platelet antigens - 2013

To date, 33 human platelet alloantigens (HPAs) have been identified on six functionally important platelet glycoprotein (GP) complexes and have been implicated in alloimmune platelet disorders including foetal and neonatal alloimmune thrombocytopenia (FNAIT), posttransfusion purpura (PTP) and multitransfusion platelet refractoriness (MPR). The greatest number of recognized HPA (20 of 33) resides on the GPIIb/IIIa complex, which serves as the receptor for ligands important in mediating haemostasis and inflammation. These include HPA-1a, the most commonly implicated HPA in FNAIT and PTP in Caucasian populations. Other platelet GP complexes, GPIb/V/IX, GPIa/IIa and CD109, express the remaining 13 HPAs. Of the recognized HPAs, 12 occur as six serologically and genetically defined biallelic 'systems' where the -a form designates the higher frequency allele and the -b form, the lower. Twenty-one other HPAs are low-frequency or rare antigens for which postulated higher frequency -a alleles have not yet been identified as antibody specificities. In addition to the HPA markers, platelets also express ABO and human leucocyte antigen (HLA) antigens; antibodies directed at the former are occasionally important in FNAIT, and to the latter, in MPR.

New K103 β3 allele identified in a context of severe neonatal thrombocytopenia

BACKGROUND

A new β3 allele was identified in a severe case of neonatal alloimmune thrombocytopenia (<7 × 10(9) /L).

STUDY DESIGN AND METHODS

Diagnosis was done by use of monoclonal antibody-specific immobilization of platelet (PLT) antigen for serologic analyses and polymerase chain reaction (PCR)-sequence-specific primers (SSP) and PCR-restriction fragment length polymorphism (RFLP) for genotyping. Direct sequencing of PCR product was done and mutant αIIbβ3 expressed in HEK-293 cells.

RESULTS

Serologic analysis revealed in the maternal serum an anti-human PLT alloantigen (HPA)-1a alloantibody associated to an anti-α2β1. Anti-HPA-1a alloimmunization diagnosis was confirmed by genotyping showing maternofetal incompatibility. However, investigation of rare HPA polymorphisms revealed discrepant HPA-16b assignation between PCR-RFLP and PCR-SSP. Sequencing revealed a new c.385C>A mutation in the β3 coding sequence resulting in a false assignation of the HPA-16b allele by PCR-RFLP. This mutation leads to a Q103K substitution in mature β3. The K103-β3 form of the complex was expressed in HEK-293 cells but did not react with the maternal serum.

CONCLUSION

We have characterized a new rare allele (frequency < 1%) of β3 that yields false HPA-16b genotyping in PCR-RFLP. This new case of false typing assignation emphasizes the necessity to use two genotyping techniques in diagnosis. This particularly applies for rare HPA polymorphisms when PLT phenotyping cannot be used.

A screening and intervention program aimed to reduce mortality and serious morbidity associated with severe neonatal alloimmune thrombocytopenia

The study's objective was to identify HPA 1a-negative women and to offer them an intervention program aimed to reduce morbidity and mortality of neonatal alloimmune thrombocytopenia (NAIT). HPA 1 typing was performed in 100 448 pregnant women. The HPA 1a-negative women were screened for anti-HPA 1a. In immunized women, delivery was performed by Cesarean section 2 to 4 weeks prior to term, with platelets from HPA 1a-negative donors reserved for immediate transfusion if petechiae were present and/or if platelet count was less than 35 x 10(9)/L. Of the women screened, 2.1% were HPA 1a negative, and anti-HPA 1a was detected in 10.6% of these. One hundred seventy pregnancies were managed according to the intervention program, resulting in 161 HPA 1a-positive children. Of these, 55 had severe thrombocytopenia (< 50 x 10(9)/L), including 2 with intracranial hemorrhage (ICH). One woman with a twin pregnancy missed the follow-up and had one stillborn and one severely thrombocytopenic live child. In 15 previous prospective studies (136 814 women) there were 51 cases of severe NAIT (3 intrauterine deaths and 7 with ICH). Acknowledging the limitation of comparing with historic controls, implementation of our screening and intervention program seemed to reduce the number of cases of severe NAIT-related complications from 10 of 51 to 3 of 57.

Cost-effectiveness of antenatal screening for neonatal alloimmune thrombocytopenia

OBJECTIVES

To estimate the costs and health consequences of three different screening strategies for neonatal alloimmune thrombocytopenia (NAIT).

DESIGN

Cost-utility analysis on the basis of a decision tree that incorporates the relevant strategies and outcomes.

SETTING

Three health regions in Norway encompassing a 2.78 million population.

POPULATION

Pregnant women (n = 100,448) screened for human platelet antigen (HPA) 1a and anti-HPA 1a antibodies, and their babies.

METHOD

Decision tree analysis. In three branches of the decision tree, pregnant women entered a programme while in one no screening was performed. The three different screening strategies included all HPA 1a negative women, only HPA 1a negative, HLA DRB3*0101 positive women or only HPA 1a negative women with high level of anti-HPA 1a antibodies. Included women underwent ultrasound examination and elective caesarean section 2-4 weeks before term. Severely thrombocytopenic newborn were transfused immediately with compatible platelets.

MAIN OUTCOME MEASUREMENTS

Quality-adjusted life years (QALYs) and costs.

RESULTS

Compared with no screening, a programme of screening and subsequent treatment would generate between 210 and 230 additional QALYs among 100,000 pregnant women, and at the same time, reduce health care costs by approximately 1.7 million euros. The sensitivity analyses indicate that screening is cost effective or even cost saving within a wide range of probabilities and costs.

CONCLUSION

Our calculations indicate that it is possible to establish an antenatal screening programme for NAIT that is cost effective.

Evaluation of a new flow cytometric HPA 1a screening method

We have evaluated a flow cytometric screening method for identification of HPA la negative individuals, using a commercially available monoclonal anti-CD61 antibody specific for the HPA 1a allotype, and compared the method with an ELISA based method for HPA la phenotyping and two methods for PCR genotyping. HPA 1a phenotyping by fluorochrome conjugated monoclonal anti-HPA la and analysis by flow cytometry is a rapid, reliable and inexpensive technique, suitable for screening purposes.

Alloimmune thrombocytopenia in the fetus: current management theories

Fetal alloimmune thrombocytopenia (AIT) affects only a small number of fetuses but the consequences may be devastating. Outcomes range from mild thrombocytopenia without signs or symptoms to intracranial hemorrhage (ICH) and fetal or neonatal death. Antenatal screening is available but not used routinely in the United States. The most frequent method of AIT identification is its diagnosis in the neonatal period (index neonate). AIT may be diagnosed antenatally if an ICH is noted on routine obstetric ultrasound. There are accurate predictors of AIT, as well as antenatal therapies, to prevent the occurrence of severe disease and ICH.

Rapid and reliable genotyping of human platelet antigen (HPA)-1, -2, -3, -4, and -5 a/b and Gov a/b by melting curve analysis

BACKGROUND

The probability for occurrence of neonatal alloimmune thrombocytopenic purpura (NAITP) depends largely on the frequency of each individual phenotype in various populations. In caucasians, antibodies to human platelet antigen (HPA)-1a are the major cause of neonatal alloimmune thrombocytopenic purpura, whereas in the Japanese population, antibodies to HPA-4b is most frequently involved in NAITP. Conventional PCR techniques for platelet antigen genotyping rely on sequence-specific primers (SSPs) and detection by gel electrophoresis, a method which is laborious and time consuming. New PCR technology, measuring the match of a hybridization probe with its target and thereby allowing simultaneous detection of both alleles, provides an efficient tool for genotyping of the HPA systems.

STUDY DESIGN AND METHODS

A total of 105 healthy blood donors were genotyped for HPA-1, -2, -3, -4, and -5 a/b and Gov a/b with new primers and probes designed for mutation detection by melting curve analysis (using LightCycler technology). Donor DNA was independently genotyped by an allele-specific assay, using SSPs, in a reference laboratory.

RESULTS

There was full concordance between the two genotyping methods, and genotype frequencies were comparable with previous studies in caucasians.

CONCLUSION

We present rapid and reliable detection systems for HPA-1, -2, -3, -4, and -5 a/b and Gov a/b based on mutation detection of both alleles simultaneously by melting curve analysis. As the Gov system has been reported to have similar frequency of involvement in alloimmune thrombocytopenia as HPA-5, the opportunity for genotyping should aid the diagnosis of such patients.