Maternal Platelet Research Articles

A case report of neonatal alloimmune thrombocytopenia: The utility of platelet crossmatch studies in the diagnosis and management

Alloimmune thrombocytopenia is the most common cause of severe thrombocytopenia and intracranial bleed in the perinatal period, resulting from placental transfer of maternal platelet antibodies directed against the paternal-derived fetal platelet antigens. It is estimated to occur in 1 in 2500 births but continues to be an underdiagnosed and underreported condition in our country. Detection of human platelet antigen-specific antibody in the maternal serum and platelet genotyping are the gold standards in the diagnosis. This case report highlights the utility of platelet crossmatch studies in the diagnosis and management of neonatal alloimmune thrombocytopenia.

Maternal Hematological Parameters and Placental and Umbilical Cord Histopathology in Intrauterine Growth Restriction

Objective: To investigate the placental and umbilical cord histopathology in intrauterine growth restriction (IUGR) and their relation to second-trimester maternal hematological parameters. Materials and Methods: Patients were selected for the IUGR group based on estimated fetal weight below the 10th percentile. Patients were recruited into the control group randomly. Patients were followed up with ultrasound, and blood samples were taken between the 20th and 24th gestational weeks. After delivery and formalin fixation, weight and volume of the placenta were recorded and histologic samples were processed. Results: Maternal platelet count strongly correlates with placental weight (r = 0.766). On the other hand, neonatal weight correlates with placental volume (r = 0.572) rather than with placental weight (r = 0.469). Umbilical arterial lumen cross-sectional area correlates with birth weight (r = 0.338). Conclusions: Maternal hematological parameters do not seem to affect neonatal outcome. Our main findings are the correlation of maternal platelet count with placental weight, the correlation of placental volume with birth weight being stronger than the correlation of placental weight with birth weight, and the correlation of umbilical artery lumen cross-sectional area with neonatal weight. Mild histopathologic alterations might occur in normal pregnancies; however, sufficient fetal nutrition can be maintained. This compensatory function of the placenta seems to be insufficient when two or more pathologies are present, which is characteristic for IUGR.

823: Risk factors associated with neonatal thrombocytopenia in pregnant women with immune thrombocytopenic purpura

To characterize the risk factors associated with neonatal thrombocytopenia among pregnant women with immune thrombocytopenic purpura (ITP). We reviewed the records of ITP patients who delivered during 2006-2016 at our medical center. Of 253 pregnancies, median maternal age at diagnosis was 29 [25-33] years, 222 (87.7%) had previously- diagnosed ITP and 31 (12.3%) were diagnosed with new-onset ITP during pregnancy. Baseline characteristics were comparable between the groups except for a higher proportion of nulliparity among those with new-onset disease (P=0.002). Maternal nadir platelet count was significantly lower among those with new-onset compared to previously diagnosed ITP (median 62 X 109/L vs. 81 X 109/L, P=0.005). Neonatal thrombocytopenia (<150 X 109/L) was encountered in 24 (9.5%) pregnancies, and required treatment in 12 (50%) of them. Neonatal platelet count was directly correlated with maternal platelet count at delivery (r=0.23, P=0.01), with significantly lower maternal platelet count among those whose newborns experienced thrombocytopenia (P<0.001). Neonatal thrombocytopenia followed a higher proportion of pregnancies of women with new-onset than previously diagnosed ITP (22.6% vs. 7.7%, P=0.02). In multivariate analysis, the presence of new-onset ITP (odds ratio [95% CI]: 4.88 (1.68, 14.16), P=0.004) was the only independent predictor of the development of neonatal thrombocytopenia. Neonatal thrombocytopenia presented following almost one-tenth of pregnancies with ITP. New pregnancy-onset disease was the only prognostic marker for neonatal thrombocytopenia. This finding could contribute to risk stratification and individualized patient management.

821: Clinical characteristics, neonatal risk and recurrence rate of gestational thrombocytopenia with platelet count

Gestational thrombocytopenia (GT) accounts for 75% of cases of thrombocytopenia in pregnancy. In most cases of GT, thrombocytopenia is mild (100-150 X 109/L) and has no consequences for either the mother or the fetus. We aimed to investigate the characteristics, neonatal risk and recurrence rate of GT with a platelet count <100 X 109/L. We reviewed the records of women who delivered during 2006-2016 at a large tertiary care university hospital, and who had platelet count <100 X 109/L during pregnancy. Of 97 pregnancies in which platelet count lower than 100 X 109/L was encountered, 66 (68%) were diagnosed as GT and 31 (32%) as new-onset immune-thrombocytopenic purpura (ITP). The proportions of women with onset of thrombocytopenia in early pregnancy (P=0.004) and a lower maternal nadir platelet count (P=0.01) were higher among those with new-onset ITP than GT. Neonatal thrombocytopenia (<100 X 109/L) was encountered following comparable proportions of pregnancies of women with new-onset ITP and GT (16.1% vs. 10.6%, P=0.51). Among women with GT, the rate of neonatal thrombocytopenia was higher in those who experienced antepartum bleeding (P=0.009) and in whom the onset of thrombocytopenia was in early pregnancy (P=0.002). Of 40 subsequent pregnancies, a recurrence of GT (<100 X 109/L) was encountered in 22 (55%), with similar maternal and perinatal outcomes compared to the initial pregnancy. The risk of neonatal thrombocytopenia was substantial and similar in GT and new-onset ITP. The recurrence rate of GT was high in subsequent pregnancies.

Risk factors associated with neonatal thrombocytopenia in pregnant women with immune thrombocytopenic purpura

Objectives: To characterize the risk factors associated with neonatal thrombocytopenia among pregnant women with immune thrombocytopenic purpura (ITP).Methods: We reviewed the records of ITP patients who delivered during 2006–2016 at our medical center.Results: Of 253 pregnancies, median maternal age at diagnosis was 29 [25–33] years, 222 (87.7%) had previously-diagnosed ITP and 31 (12.3%) were diagnosed with new-onset ITP during pregnancy. Baseline characteristics were comparable between the groups except for a higher proportion of nulliparity among those with new-onset disease (p = .002). Maternal nadir platelet count was significantly lower among those with new-onset compared to previously diagnosed ITP (median 62 × 109/L versus 81 × 109/L, p = .005). Neonatal thrombocytopenia (<150 × 109/L) was encountered in 24 (9.5%) pregnancies and required treatment in 12 (50%) of them. Neonatal platelet count was directly correlated with maternal platelet count at delivery (r = 0.23, p = .01), with significantly lower maternal platelet count among those whose newborns experienced thrombocytopenia (p < .001). Neonatal thrombocytopenia followed a higher proportion of pregnancies of women with new-onset than previously diagnosed ITP (22.6 versus 7.7%, p = .02). In multivariate analysis, the presence of new-onset ITP (odds ratio [95% CI]: 4.88 (1.68, 14.16), p = .004) was the only independent predictor of the development of neonatal thrombocytopenia.Conclusion: Neonatal thrombocytopenia presented following almost one-tenth of pregnancies with ITP. New pregnancy-onset disease was the only prognostic marker for neonatal thrombocytopenia. This finding could contribute to risk stratification and individualized patient management.

Clinical characteristics, neonatal risk and recurrence rate of gestational thrombocytopenia with platelet count

ObjectiveGestational thrombocytopenia (GT) accounts for 75% of cases of thrombocytopenia in pregnancy. In most cases of GT, thrombocytopenia is mild (100–150 × 109/L) and has no consequences for either the mother or the fetus. We aimed to investigate the characteristics, neonatal risk and recurrence rate of GT with a platelet count <100 × 109/L. Study DesignWe reviewed the records of women who delivered during 2006–2016 at a large tertiary care university hospital, and who had platelet count <100 × 109/L during pregnancy. ResultsOf 97 pregnancies in which platelet count lower than 100 × 109/L was encountered, 66 (68%) were diagnosed as GT and 31 (32%) as new-onset immune-thrombocytopenic purpura (ITP). The proportions of women with onset of thrombocytopenia in early pregnancy (P = 0.004) and a lower maternal nadir platelet count (P = 0.01) were higher among those with new-onset ITP than GT. There was no difference in the rate of neonatal thrombocytopenia (<100 × 109/L) between those with newly diagnosed ITP and GT (16.1% vs. 10.6%, P = 0.51). Among women with GT, the rate of neonatal thrombocytopenia was higher in those who experienced antepartum bleeding (P = 0.009) and in whom the onset of thrombocytopenia was in early pregnancy (P = 0.002). Of 40 subsequent pregnancies, a recurrence of GT (<100 × 109/L) was encountered in 22 (55%), with similar maternal and perinatal outcomes compared to the initial pregnancy. ConclusionThe risk of neonatal thrombocytopenia was substantial, with no difference found between those with GT and new-onset ITP. The recurrence rate of GT was high in subsequent pregnancies.

449. Management of microangiopathic haemolytic anaemia in pregnancy

Microangiopathic haemolytic anaemia (MAHA) refers to haemolytic anaemia caused by small arteriole endothelial dysfunction. Pregnancy-induced changes to maternal vasculature, coagulation and immunity predispose women to MAHA. Materno-fetal disease follows platelet consumption within microthrombi of arterioles to end-organs and is often organ-specific. The key to successful management is accurate diagnosis. MAHA and microthrombi within the utero-placental circulation is associated with pre-eclampsia. Childbirth is the cure, but management is supportive until maternal or fetal condition deteriorate, or when fetal maturity is considered sufficient for ex-utero survival. HELLP syndrome describes the pathological components of MAHA affecting the liver. It presents suddenly with acute hepatic pain and an acute rise in liver transaminases with platelet consumption. HELLP is often associated with placental dysfunction, fetal growth restriction and hypertension. Management is similar to preeclampsia management. Steroids may improve the maternal platelet count and reduce the risk of peripartum bleeding. MAHA and microthrombi within the brain is suggestive of thrombotic thrombocytopaenic purpura (TTP). Women present with neurological symptoms, headache and seizures. TTP is secondary to low level of metalloproteinase ADAMTS13, which cleaves the endothelial von Willebrand factor and prevents platelet microthrombi. Levels of ADAMTS13 fall during pregnancy such that women with a congenital deficiency, or with autoantibodies against ADAMTS13, are predisposed to peripartum TTP. Treatment is plasma exchange. MAHA and microthrombi within the kidneys is suggestive of haemolytic uraemic syndrome (HUS). Pregnant women present with hypertension and acute kidney injury. Treatment of atypical HUS has been transformed by the introduction of Eculizimab that targets a component of the complement system. Acute fatty liver of pregnancy (AFLP) is a metabolic disorder characterised by a defect in fat metabolism. AFLP presents with multi-organ failure. This lecture will use a case-based approach to highlight features that discriminate between MAHA and allow implementation of targeted therapies to improve pregnancy outcome.

Impact of fetal maceration grade on risk of maternal disseminated intravascular coagulation after intrauterine fetal death \u2013 A retrospective cohort study

Disseminated intravascular coagulation (DIC) is a life-threatening event that is the endpoint of a pathologically activated cascade leading to excessive consumption of platelets culminating in bleeding. Several diseases are known to be associated with DIC, some of which may also occur during pregnancy or the puerperium. One of the potential risk factors that have been considered as a potential trigger for DIC is the retention of a highly macerated fetus after intrauterine fetal death (IUFD). However, sparse evidence exists on its clinical implication on hemostasis parameters. In this retrospective single-center study, we investigated the role of fetal maceration grades 0-III on the risk of DIC in 91 women following IUFD between gestational weeks (+days) 22 + 0 and 41 + 6 between 2003 and 2017. We calculated the Erez DIC-score after consideration of maternal platelet count (PC), prothrombin time (PT) and fibrinogen (Fib) and correlated the findings with fetal maceration grade. Mean (±SD) age of women was 32.1 ± 6.7 years. Neither maternal hemostasis parameters (PC, PT, Fib), nor the Erez score showed a statistically significant difference between maceration grades 0-III with median values of 1 for all four grades (maceration grade I: range 0 to 27; I: 0 to 51; II: 0 to 52; III: 0 to 39). We therefore conclude, that the pathophysiology of DIC in women after singleton IUFD is unrelated to the degree of fetal maceration.

THE ROLE OF INTERACTIONS BETWEEN TROPHOBLASTDERIVED EXTRACELLULAR MICROVESICLES, IMMUNE CELLS AND ENDOTHELIUM IN PATHOGENESIS OF PRE-ECLAMPSIA

Pre-eclampsia is a multisystemic disease that occurs in the second half of pregnancy, being characterized by the development of hypertension and proteinuria. Pre-eclampsia is still one of the main causes of maternal and neonatal morbidity and mortality. Pre-eclampsia is believed to be a result of complex interactions between maternal and placental factors. However, the exact pathophysiology of this syndrome remains unclear. Intercellular interactions are the basis of fetoplacental development in physiological pregnancy. A special mechanism of intercellular interactions is associated with the release of membranebound extracellular microvesicles by cells. Concentration and molecular composition of extracellular vesicles in biological fluids depend on the producer cell types, as well as the stimuli that trigger their formation. The studies of extracellular vesicles in pre-eclampsia focus on the particles produced by the cells of maternal cardiovascular system (endothelium, smooth muscle cells of blood vessels), and blood (erythrocytes, leukocytes, and platelets), like as by the cells of syncytiotrophoblast. Changed concentrations and molecular composition of these extracellular vesicles can contribute to the pathophysiology of pre-eclampsia, due to increased proinflammatory and procoagulant state occurring during pregnancy. This review focuses, firstly, on characteristics of the extracellular vesicles produced by syncytiotrophoblast, and possible role of their interaction with maternal immune cells, endothelial cells and platelets in the course of developing pre-eclampsia. Understanding the role of extracellular vesicles of syncytiotrophoblast in pathogenesis of pre-eclampsia could suggest an opportunity of providing these results for early and non-invasive diagnostics of placental disorders, as well as for predicting development of this disease.

A longitudinal, cross-sectional study of diversity in maternal platelet count kinetics, related to gestational thrombocytopenia

A longitudinal, cross-sectional study of diversity in maternal platelet count kinetics, related to gestational thrombocytopenia

Intracranial Hemorrhage and Autoimmune Thrombocytopenia in a Neonate: A Rare "Unpredictable" Event.

Neonatal thrombocytopenia is a rare complication of maternal autoimmune thrombocytopenia, and no maternal predictors of its gravity and potential complications have been identified. Neonatal cerebral hemorrhage, a feared event in the setting of autoimmune thrombocytopenia, is fortunately uncommon, but it can occur in utero or in the perinatal period, with potentially serious consequences. The authors report the case of a boy born to a mother affected by autoimmune thrombocytopenia, who presented with severe thrombocytopenia at birth and developed intracranial hemorrhage despite mild maternal thrombocytopenia at delivery and a prompt preventive treatment of the newborn. Platelet count should be tested at birth in all babies born from mothers with autoimmune thrombocytopenia, irrespective of maternal platelets counts during pregnancy or at delivery, and should be closely monitored during the first days of life. Systematic early and serial cranial ultrasound might be advocated in the setting of neonatal thrombocytopenia.

The altered platelet mineral ratios in pregnancy complicated with intrauterine growth restriction

Altered function of maternal platelets has been evidenced in intrauterine growth restriction (IUGR) but intraplatelet burden of trace elements, factors known to affect platelet activity, remains unknown in IUGR pregnancy. This study assessed the intraplatelet status of Ca, Cu, Mg, Na, K, P, Zn and their ratios (Ca/P, Ca/Mg, Na/K, Cu/Zn) in IUGR pregnancy (n = 35), uncomplicated pregnancy (n = 25) and in non-pregnant females (n = 25). The IUGR group was characterized by the lowest content of Ca, Mg and Zn, and Ca/P ratio (<1.0), and the highest Ca/Mg and Cu/Zn ratios. The studied parameters in non-pregnant women and in uncomplicated pregnancy were comparable except P content and Ca/Mg ratio which were significantly lower in the former group. No differences in Na and K contents, and Na/K ratio between studied groups were found. This study reports that maternal intraplatelet status of selected minerals may be altered in IUGR.

Severe neonatal thrombocytopenia due to fetomaternal anti-A alloimmunization: A case report

Severe neonatal thrombocytopenia due to fetomaternal anti-A alloimmunization: A case report

Intracranial hemorrhages in neonates born from 32 weeks of gestation-low frequency of associated fetal and neonatal alloimmune thrombocytopenia: a register-based study.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare condition, with an estimated incidence of one in 1000 to 2000 live births. Predominantly, FNAIT is due to maternal alloantibodies that target paternally derived human platelet antigen (HPA) 1a. The most feared complication is an intracranial hemorrhage (ICH). The aim of this study was to determine the frequency of associated maternal platelet (PLT) alloimmunization in a population of neonates born from 32 weeks of gestation and diagnosed with an ICH. The Swedish Neonatal Quality (SNQ) register was used to identify neonates diagnosed with an ICH born between 2003 and 2012. Mothers were invited to donate peripheral blood, to investigate their HPA-1a antigen status, and test for anti-HPA and anti-HLA Class I alloantibodies. Clinical data for the neonates were retrieved from the SNQ register and available clinical records. Of 286 registered neonates, 278 mothers were contacted. Of 105 analyzed maternal samples, two (1.9%) were HPA-1a antigen negative. Antibody analyses revealed in total three (2.9%) mothers with anti-HPA: one mother (0.94%) with anti-HPA-1a and two mothers (1.9%) with anti-HPA-5b, of whom one had concurrent anti-HPA-15a. Twenty-four percent tested positive for anti-HLA Class I antibodies. A total of 8.5% of neonates (5/59) with PLT counts available in clinical records were severely thrombocytopenic, with PLT counts of less than 50 × 109 /L. This retrospective cohort revealed a wide range of factors associated with ICH in neonates born from 32 weeks of gestation and suggests PLT alloimmunization to be a less common contributor than anticipated.

Maternal and fetal outcomes of primary immune thrombocytopenia during pregnancy: A retrospective study

We reviewed outcomes of 52 pregnancies in 45 women with immune thrombocytopenic purpura who delivered at Auckland Hospital with an antenatal platelet count of <100 × 109/L. Primary outcomes were maternal platelet count at delivery and treatment response. Secondary outcomes included post-partum haemorrhage (PPH). Most women had thrombocytopenia at delivery. Treatment with prednisone was given in 14 (27%) pregnancies with responses considered safe for delivery in 11 pregnancies (79%). Women in eight pregnancies also received intravenous immunoglobulin; in five pregnancies (63%) a platelet response acceptable for delivery was achieved.Seventeen pregnancies (33%) were complicated by a PPH ≥500 mL. Ten pregnancies (19%) were complicated by a PPH ≥1000 mL. PPH was reported in all women with a platelet count <50 × 109/L at delivery. There were no antenatal bleeding complications but PPH was common among women with platelet counts <50 × 109/L at the time of birth.

Fetal exposure to maternal human platelet antigen-1a does not induce tolerance. An analytical observational study.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a disease that may cause severe bleeding complications with risk of perinatal death or lifelong disability. The main cause of FNAIT is maternal antibodies against human platelet antigen (HPA)-1a. Both fetomaternal bleeding and transplacental trafficking of fetal cells during pregnancy could be the cause of alloimmunization. Persistence of fetal cells in the mother (fetal microchimerism) and maternal cells in the child (maternal microchimerism) are well-recognized phenomena. Thus, it could be envisaged that fetal exposure to the HPA-1a antigen could tolerize an HPA-1a negative female fetus and prevent production of anti-HPA-1a antibodies later in life if she becomes pregnant with an HPA-1a positive fetus. The objective of the current study was to assess if the risk of producing anti-HPA-1a antibodies and the severity of neonatal thrombocytopenia in HPA-1a negative women with HPA-1a positive mothers (i.e. the mother is HPA-1a/b), was lower than in HPA-1a negative women with HPA-1a negative mothers. HPA-1a negative women with HPA-1a antibodies, identified from a Norwegian screening study (1996–2004), where HPA-1 genotype of their mothers was available, were included in the study. The frequency of HPA-1a positive mothers to HPA-1a immunized daughters were compared to the calculated frequency in the general population. We did not find any difference in the frequency of HPA-1ab among mothers to daughters with HPA-1a antibodies as compared with the general population. Furthermore, acknowledging sample-size limitations, we neither found an association between the mothers’ HPA type and their daughters’ anti-HPA-1a antibody levels or any difference between the two groups of mothers (HPA-1ab vs HPA-1bb), with respect to frequency of thrombocytopenia in the children of their daughters with HPA-1a antibodies. Hence, there was no indication of tolerance against fetal HPA-1a antigen in HPA-1bb women who had been exposed to HPA-1a antigen during fetal development.

Association of intrapartum maternal mean platelet volume with neonatal birth weight

Purpose: To investigate the relationship between neonatal birth weight (NBW) and intrapartum maternal mean platelet volume (MPV). Materials and Methods: A total of 650 women who had a live birth at the Etlik Zubeyde Hanım Women's Health Education and Research Hospital in Ankara were divided into three groups according to the babies'birth weight adjusted for gestational week: 145 delivered small for gestational age (SGA) (th percentile), 363 delivered appropriate for gestational age (AGA) (10-90th percentile), and 142 delivered large for gestational age (LGA) babies (> 90th percentile). Maternal MPV value of the women were taken into account together with demographic values, body mass index (BMI), and gestational age at delivery and birth weight. Results: MPV was found to be significantly higher in the mothers of LGA babies (9.69 ± 1.11) in comparison to SGA (9.38 ± 1.03) and AGA (9.36 ± 1.09) babies in the statistical analysis (p = 0.009). More than 9.65 fL value of intrapartum maternal MPV was associated with LGA. Conclusion: MPV was increased in the intrapartum period in women who delivered LGA babies.

Immunohistochemical study of endometrial immune cells in patients with chronic endometritis with recurrent miscarriage

Anti-HLA class I antibodies have been suggested as a possible cause of fetal and neonatal alloimmune thrombocytopenia (FNAIT). The aim of this study was to characterize maternal anti-HLA class I alloantibodies in suspected cases of FNAIT.The study population consisted of all nationwide referrals of neonates with suspected FNAIT to the National Unit for Platelet Immunology in Tromsø, Norway, during 1998–2009 (cases), and 250 unselected pregnancies originally included in a prospective study (controls). Inclusion criterion was a positive screening for maternal anti-HLA class I antibodies. Neonates with other identifiable causes of thrombocytopenia, including maternal anti-human platelet antigens (HPA) antibodies, were excluded. Ultimately, 50 cases with suspected FNAIT were compared with 60 controls.The median neonatal platelet count nadir among cases was 24 × 109/L (range 4–98 × 109/L). Five children (10%) were reported to have intracranial hemorrhage. Maternal and neonatal HLA class I genotype was available for 33 mother/child pairs (66%). Immunization was not tied to any particular HLA class I antigen. Using epitope mapping, we could demonstrate that the maternal anti-HLA class I antibodies were specific towards mismatched paternally-inherited fetal epitopes, with little reactivity towards any third-party epitopes. Antibody reactivity patterns were similar to those found among controls, although the mean fluorescence intensities (MFI) among cases were significantly higher.This study demonstrates the value of using data on HLA epitope expression, instead of HLA antigens, to examine alloimmune responses in connection with neonatal thrombocytopenia. Our findings support the idea that maternal anti-HLA class I antibodies are involved in FNAIT.

Reproductive cycle-dependent expression of MHC and TCR in vaginal fluid and cells

Anti-HLA class I antibodies have been suggested as a possible cause of fetal and neonatal alloimmune thrombocytopenia (FNAIT). The aim of this study was to characterize maternal anti-HLA class I alloantibodies in suspected cases of FNAIT.The study population consisted of all nationwide referrals of neonates with suspected FNAIT to the National Unit for Platelet Immunology in Tromsø, Norway, during 1998–2009 (cases), and 250 unselected pregnancies originally included in a prospective study (controls). Inclusion criterion was a positive screening for maternal anti-HLA class I antibodies. Neonates with other identifiable causes of thrombocytopenia, including maternal anti-human platelet antigens (HPA) antibodies, were excluded. Ultimately, 50 cases with suspected FNAIT were compared with 60 controls.The median neonatal platelet count nadir among cases was 24 × 109/L (range 4–98 × 109/L). Five children (10%) were reported to have intracranial hemorrhage. Maternal and neonatal HLA class I genotype was available for 33 mother/child pairs (66%). Immunization was not tied to any particular HLA class I antigen. Using epitope mapping, we could demonstrate that the maternal anti-HLA class I antibodies were specific towards mismatched paternally-inherited fetal epitopes, with little reactivity towards any third-party epitopes. Antibody reactivity patterns were similar to those found among controls, although the mean fluorescence intensities (MFI) among cases were significantly higher.This study demonstrates the value of using data on HLA epitope expression, instead of HLA antigens, to examine alloimmune responses in connection with neonatal thrombocytopenia. Our findings support the idea that maternal anti-HLA class I antibodies are involved in FNAIT.

Cab4b, the first human platelet antigen carried by glycoprotein IX discovered in a context of severe neonatal thrombocytopenia

Background After three miscarriages, a 39-year-old woman gave birth, with a 1-year interval, to two severely thrombocytopenic neonates (4 ×109 L-1 and 33 ×109 L-1 ) with intracranial hemorrhages. Transfusion of platelet concentrates corrected the thrombocytopenia. The outcome was favorable for the first child, but the second one died 10 days after cesarean delivery (31 weeks of gestation + 6 days). Methods Serologic studies were performed with mAb-specific immobilization of platelet antigens and flow cytometry techniques. Human platelet alloantigen (HPA) genotyping was performed with the BioArray HPA BeadChip and PCR-sequence-specific primer techniques. Genomic DNA was studied by direct sequencing of PCR products. The mutant glycoprotein (GP) was expressed in transiently transfected HEK293 cells. Results In MAIPA assay, the maternal serum faintly reacted with GPIbIX from paternal and child 1 platelets, but not with maternal or panel platelets. No maternofetal incompatibility was found in the 22 known HPA systems, tested except for HPA-1b in child 2. A new alloantigen carried by GPIbIX was suspected. Genomic sequencing revealed a paternal GPIX variation (NM_000174.4:c.368C>T). The father and children were heterozygous and incompatible with the mother, who was NM_000174.4:c.368C homozygous. The maternal serum reacted with the GPIX NP_000165.1:p.Leu123 form coexpressed with GPIb in transfected HEK293 cells. The NM_000174.4:c.368T allele (rs202229101) has a minor allele frequency of 0.0002, and was not detected in 120 French subjects (families with fetal and neonatal alloimmune thrombocytopenia [FNAIT]), suggesting that it is rarely implicated in alloimmunization. Conclusion The NP_000165.1:p.Leu123 allele named Cab4b is the first platelet alloantigen described on GPIX. In the absence of other known maternofetal incompatibility, the child 1 case suggests that anti-Cab4b alloantibodies can induce severe thrombocytopenias.