Impaired platelet function among platelet donors.

BACKGROUND: Platelet transfusions are effective for the prevention and treatment of bleeding in patients with disorders of platelet number and/or function. In recent years plateletpheresis concentrates have outnumbered pooled platelet concentrates, albeit with significant differences between nations. Thus, the platelet quality of individual donors has become increasingly important. The aim of this study was to gain an estimate for the prevalence of impaired platelet function among platelet donors. STUDY DESIGN AND METHODS: We determined the inter-donor variability in platelet plug formation with a PFA-100 analyzer, the prevalence of impaired thromboxane formation, and effects of the density in alpha2 integrin polymorphism and density. RESULTS: (i) Collagen-epinephrine induced closure time (CEPI-CT) showed a great inter-subject variability in platelet donors and was higher than in healthy controls (p = 0.008). One-fifth of donors had abnormal CEPI-CT values and 11% exceeded >300 s (max measurable value). (ii) Decreased serum thromboxane B2 levels were found in 9% of all donors, compatible with surreptitious intake of cyclooxygenase inhibitors or with an aspirin-like defect. CEPI-CT correlated inversely with TxB2-levels in donors and controls. (iii) The density of the alpha2-integrin correlated negatively with CEPI-CT and CADP-CT values in controls, but was not responsible for the observed impaired platelet function in donors. (iv) Finally, the ABO blood group system modulates closure times. CONCLUSION: In sum, a large number of platelet donors present with prolonged closure times. Decreased thromboxane formation and frequent platelet donation partly account for this observation.

The platelet alpha2-integrin (GPIa) nucleotide-807 polymorphism is not associated with a risk for maternal-fetal human platelet antigen-5 incompatibility.

Alloimmunization against human platelet antigen (HPA)-5 may lead to neonatal alloimmune thrombocytopenia. The HPA-5 dimorphism is expressed on the platelet alpha2beta1 integrin. The density of this receptor is associated with another dimorphism of the 2beta1 integrin (nucleotide-807C/T). We hypothesized that anti-HPA-5b-induced neonatal thrombocytopenia is more likely to occur if the receptor is expressed at high than at low levels. Among 933 mother-child pairs, we identified 79 HPA-5aa mothers giving birth to a HPA-Sab offspring. Seventeen mothers had HPA-5b antibodies, but the offspring had a normal platelet count. We genotyped the offspring and mothers for the alpha2-807C/T dimorphism to evaluate its relationship to antibody formation. There was no difference between the frequency of the 807C/T dimorphism among children delivered from alloimmunized mothers and those from mothers without antibodies (P>0.3). The frequency of the 807C/T dimorphism was not different in the two maternal groups. In three maternal-fetal incompatibilities, we observed at delivery normal platelet counts of platelets typed HPA-5b-alpha2807T, despite increasing maternal antibody titers during the pregnancy. Our data do not support the hypothesis that the 807C/T dimorphism in the HPA-5ab children is a predisposing factor to either elicit alloimmunization against HPA-5b or for neonatal alloimmune thrombocytopenia.

Platelet glycoprotein Ia gene dimorphism alpha2-807 in malignant arrhythmia in coronary artery disease.

It has been shown recently that the variable expression of the platelet collagen receptor integrin alpha2beta1 predisposes to thrombotic risk on the one hand and hemorrhagic risk on the other hand. The level of expression of the integrin alpha2beta1 is genetically controlled and associated with the alpha2-807 dimorphism. The expression level of this platelet collagen receptor may play a central role in the rapidly evolving coronary artery lesions that lead to malignant arrhythmia and sudden cardiac death. We studied allelic frequencies of the alpha2-807 dimorphism for their relation as a risk factor for malignant arrhythmia in a well-defined subgroup of patients with coronary artery disease. We compared allelic frequencies (by sequence specific primer polymerase chain reaction) of the dimorphism that is associated with integrin alpha2beta1 levels in 94 Caucasoid survivors of sudden cardiac death with a matched group of 106 patients with coronary artery disease without sudden cardiac death. Gene frequencies in the patient groups did not differ and were similar to those in the general population represented by 217 healthy individuals. There was no overrepresentation of an allele in any group. The inherited dimorphism that is associated with the levels of platelet integrin alpha2beta1 is not associated with malignant arrhythmia in coronary artery disease patients.

Calcaneal ultrasound attenuation and vitamin-D-receptor genotypes in celiac disease.

BACKGROUND: Osteopenia is common in patients with celiac disease and is believed to result from malnutrition. Osteoporosis in otherwise healthy individuals is related to genetically determined polymorphisms within the vitamin-D-receptor (VDR) gene. We hypothesized that in celiac patients particular genes of the VDR enhance the susceptibility for malnutrition-associated low-bone density. METHODS: We determined allelic frequencies within the VDR gene by restriction fragment length polymorphism analysis in 92 patients with celiac disease (age, 15-83 years). Thirty-eight patients were on a gluten-free diet; 54 patients did not adhere to a diet. The determined VDR polymorphisms in 111 unrelated newborns served as controls. Osteopenia was determined by means of ultrasound measurements of the calcaneus (n = 78). Bone turnover was estimated by osteocalcin determination (n = 60). RESULTS: There was no difference in the frequency of the VDR gene polymorphisms in patients with celiac disease compared with controls. Adjusted ultrasound measures of the calcaneus were low in 47% of patients, but there was no difference of the VDR gene frequencies in these patients compared with those with normal ultrasound results or controls. Bone turnover was higher in patients without a gluten-free diet (P = 0.02). Again, there was no association with any particular VDR gene. CONCLUSIONS: Patients with celiac disease frequently have osteopenia, which is not related to any of the determined genes within the VDR.

Screening for platelet auto-antibodies by flow cytometry and their evaluation by the MAIPA technique.

The determination of platelet antibodies assists in the diagnosis of immune thrombocytopenia. Among the various techniques which have been used two major ways for the determination of these antibodies have entered the routine use, determination of in vivo platelet bound total IgG, termed platelet-associated IgG, PAIgG, and that of specifically to particular platelet glycoproteins bound IgG, GP-IgG. The former has been found to be non-specific, and the evaluation of the latter is rather laborious. Furthermore, both require a large number of platelets. By flowcytometry, however, PAIgG can be determined even if platelet counts are very low. We therefore evaluated in 30 patients' samples if the flowcytometric determination of PAIgG can serve to screen for platelet antibodies. Positive samples subsequently are evaluated by a glycoprotein-specific detection technique (MAIPA). We show that in patients with suspected autoimmune thrombocytopenia (AITP) and in secondary AITP PAIgG is elevated in 83%. However, only 30% of patients' samples have detectable antibodies by the MAIPA technique. Based on the findings that by the MAIPA technique antibodies were only detectable in samples which had also elevated levels of PAIgG we consider the flowcytometric determination of PAIgG useful for screening, prior to the more laborious investigation by the MAIPA assay.

Inherited platelet glycoprotein polymorphisms and a risk for coronary heart disease in young central Europeans.

Among central Europeans polymorphisms of GPIIIa, GPIb, GPIIb, and GPIa named human platelet antigen-1 (HPA-1), -2, -3, and -5 are the clinically most relevant systems in which alloimmunization occurs. These genetically determined polymorphisms of glycoproteins may render platelets sensible for plaque formation and thus could increase risk for coronary artery disease (CAD). We therefore determined gene frequencies of HPA-1, -2, -3, and -5 in European patients suffering from CAD (n = 92; median age, 46 years) or CAD accompanied by diabetes mellitus (DM) (n = 30; median age, 60 years, DM I/II, 5/25) and compared the data obtained with those in DM patients without CAD (n = 80; median age, 43 years; DM I/II, 53/27) and a control group (newborns, n = 906). Triglyceride and cholesterin levels as well as the percentage of smokers was significantly higher in the CAD group compared with the diabetics without DM (p < 0.005). No significant difference of the frequencies of any HPA-type between CAD patients with or without DM, diabetics, or controls could be detected. This was also true when evaluating a subgroup of patients aged 45 years or younger. To include a mutual influence of the described HPA-polymorphisms, we condensed the four HPA genotypes to joint glycoprotein variants. Again the same frequencies were found in patient groups and controls, when analyzing the five most common condensed joint glycoprotein variants. The analysis of the combined published studies shows that the pooled HPA-1 allele frequencies are identical in controls and CAD patients. Thus, no significant association between the polymorphisms of any of the studied HPA systems and the development of CAD can be found in central Europeans.