Prenatal Management of Pregnancies at Risk of Fetal Neonatal Alloimmune Thrombocytopenia (FNAIT): Scientific Impact Paper No. 61.

WHAT IS IT?: Fetal neonatal alloimmune thrombocytopenia (FNAIT), also known as neonatal alloimmune thrombocytopenia (NAIT) or fetomaternal alloimmune thrombocytopenia (FMAIT), is a rare condition which affects a baby's platelets. This can put them at risk of problems with bleeding, particularly into the brain. One baby per week in the UK may be seriously affected and milder forms can affect one in every 1000 births. HOW IS IT CAUSED?: Platelets are blood cells that are very important in helping blood to clot. All platelets have natural proteins on their surface called human platelet antigens (HPAs). In babies, half of these antigens are inherited from the mother and half from the father. During pregnancy, some of the baby's platelets can cross into the mother's bloodstream. In most cases, this does not cause a problem. But in cases of FNAIT, the mother's immune system does not recognise the baby's HPAs that were inherited from the father and develops antibodies, which can cross the placenta and attack the baby's platelets. These antibodies are called anti-HPAs, and the commonest antibody implicated is anti-HPA-1a, but there are other rarer antibody types. If this happens, the baby's platelets may be destroyed causing their platelet count to fall dangerously low. If the platelet count is very low there is a risk to the baby of bleeding into their brain before they are born. This is very rare but if it happens it can have serious effects on the baby's health. HOW IS IT INHERITED?: A baby inherits half of their HPAs from its mother and half from its father. Consequently, a baby may have different HPAs from its mother. As the condition is very rare, and even if the baby is at risk of the condition we have no way of knowing how severely they will be affected, routine screening is not currently recommended. WHAT CAN BE DONE?: FNAIT is usually diagnosed if a previous baby has had a low platelet count. The parents are offered blood tests and the condition can be confirmed or ruled out. There are many other causes of low platelets in babies, which may also need to be tested for. As the condition is so rare, expertise is limited to specialist centres and normally a haematologist and fetal medicine doctor will perform and interpret the tests together. Fortunately, there is an effective treatment for the vast majority of cases called immunoglobulin, or IVIg. This 'blood product' is given intravenously through a drip every week to women at risk of the condition. It may be started from as early as 16 weeks in the next pregnancy, until birth, which would be offered at around 36-37 weeks. Less common treatments that may be considered depending on individual circumstances include steroid tablets or injections, or giving platelet transfusions to the baby. WHAT DOES THIS PAPER TELL YOU?: This paper considers the latest evidence in relation to treatment options in the management of pregnancies at risk of FNAIT. Specifically, we discuss the role of screening, when IVIg should be started, what dose should be used, and what evidence there is for maternal steroids. We also consider in very rare selected cases, the use of fetal blood sampling and giving platelet transfusions to the baby before birth. Finally, we consider the approaches to blood testing mothers to tell if babies are at risk, which is offered in some countries, and development of new treatments to reduce the risk of FNAIT.

Noninvasive prenatal diagnosis by cell-free DNA screening for fetomaternal HPA-1a platelet incompatibility.

BACKGROUND: The development of new noninvasive approaches for the diagnosis of human platelet antigen (HPA)-1 fetomaternal incompatibility has become of great interest. These approaches allow determination of whether the fetus is incompatible or not with the mother and a decision on antenatal therapy to avoid fetal or neonatal alloimmune thrombocytopenia (FNAIT). The objective of this work was to perform rapid, noninvasive prenatal test for HPA-1ab fetal antigen detection after the detection of an HPA-1-homozygous mother by using plasma cell-free DNA (cfDNA). STUDY DESIGN AND METHODS: The HPA-1 genotypes of 142 pregnant women and 17 nonpregnant controls were retrospectively determined by high-resolution melting (HRM) polymerase chain reaction (PCR). Coamplification at lower denaturation temperature (COLD) HRM PCR was performed to determine the fetal genotype analyzing cfDNA from all HPA-1bb pregnant women. RESULTS: After the HRM analysis, the following genotypes were identified: HPA-1aa (71.13%), HPA-1bb (2.8%), and HPA-1ab (26.06%). Four HPA-1bb-homozygous pregnant women were carrying an incompatible fetus. Plasma samples from these mothers were analyzed by HRM COLD-PCR. Homozygous HPA-1bb pregnant women carrying an HPA-1ab-heterozygous fetus did not group with either the HPA-1ab or the HPA-1bb controls. Thus, COLD-PCR analysis allows the detection of HPA-1ab-heterozygous fetuses carried by homozygous mothers during first weeks of pregnancy. CONCLUSION: The fetal genotype from HPA-1bb-homozygous women was detected by a noninvasive prenatal test as soon as 12 weeks of gestation.

Maternal anti-platelet ß3 integrins impair angiogenesis and cause intracranial hemorrhage.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a life-threatening disease in which intracranial hemorrhage (ICH) is the major risk. Although thrombocytopenia, which is caused by maternal antibodies against ß3 integrin and occasionally by maternal antibodies against other platelet antigens, such as glycoprotein GPIbα, has long been assumed to be the cause of bleeding, the mechanism of ICH has not been adequately explored. Utilizing murine models of FNAIT and a high-frequency ultrasound imaging system, we found that ICH only occurred in fetuses and neonates with anti-ß3 integrin-mediated, but not anti-GPIbα-mediated, FNAIT, despite similar thrombocytopenia in both groups. Only anti-ß3 integrin-mediated FNAIT reduced brain and retina vessel density, impaired angiogenic signaling, and increased endothelial cell apoptosis, all of which were abrogated by maternal administration of intravenous immunoglobulin (IVIG). ICH and impairment of retinal angiogenesis were further reproduced in neonates by injection of anti-ß3 integrin, but not anti-GPIbα antisera. Utilizing cultured human endothelial cells, we found that cell proliferation, network formation, and AKT phosphorylation were inhibited only by murine anti-ß3 integrin antisera and human anti-HPA-1a IgG purified from mothers with FNAIT children. Our data suggest that fetal hemostasis is distinct and that impairment of angiogenesis rather than thrombocytopenia likely causes FNAIT-associated ICH. Additionally, our results indicate that maternal IVIG therapy can effectively prevent this devastating disorder.

[PREVFNAIT prevention of foetal/neonatal alloimmune thrombocytopenia (FNAIT) in Polish foetuses and newborns--the PREVFNAIT program]. / Zapobieganie alloimmunologicznej maloplytkowosci plodów i noworodków (AIMPN) w Polsce--program PREVFNAIT.

The scientific goals related to the grant include 1) estimation of FNAIT prevalence in Poland and 2) search for biomarkers to predict the risk of the antibody production and severity of fetal thrombocytopenia. Fetal/Neonatal Alloimmune Thrombocytopenia (FNAIT) is caused by destruction of fetal blood platelets due to maternal antibodies. This condition, which most commonly results from incompatibility between the mother and the fetus for the Human Platelet Antigen-1a (HPA-1a), may lead to intracranial hemorrhage, damage of the central nervous system (CNS) and even death of the fetus or the newborn. It can be the cause of strokes in term newborns. FNAIT is usually attributed to the presence of anti-HPA-1a antibodies. Its incidence rate is estimated at approximately 1/1000-2000 live births. In the absence of a screening program, it is usually diagnosed after birth of a child with symptoms of thrombocytopenia or CNS hemorrhage. Monitoring of antibody production and thrombocytopenia treatment to effectively minimize the risk of stroke are therefore launched only at the next pregnancy. Testing indications are broader to include fetal ultrasound for symptoms of stroke to the CNS, ventricular enlargement or hydrocephalus, and obstetric failure. Diagnostic process is also recommended prior to the planned cordocentesis, in vitro fertilization and in sisters of mothers with children with FNAIT history. HPA-1a testing remains the best method for diagnosing pregnancies at risk. The detection frequency for FNAIT in Poland remains low. Therefore, the Institute of Hematology and Transfusion Medicine (IHTM) will have performed such HPA-1a antigen testing in 30 000 Polish women within the framework of the PREVFNAIT program by March 2016. HPA-1a negative women (2% of the population) are a risk group for production of anti- HPA-1a antibodies responsible for FNAIT therefore all of them will be monitored for the presence and activity of anti-HPA-1a antibodies. Such testing will be performed free of charge for the women.

Preimplantation genetic diagnosis for fetal neonatal alloimmune thrombocytopenia due to antihuman platelet antigen maternal antibodies.

OBJECTIVE: To develop a reliable preimplantation genetic diagnosis protocol for antihuman platelet antigen-1 incompatibility for a family in whom antenatal treatment was not possible because of the mother's hypersensitivity to intravenous immunoglobulin (IVIG). METHODS: Haplotypes were constructed from genomic DNA of the family members. A polymerase chain reaction protocol that included eight microsatellite polymorphic markers and the ITGB3-specific (T196C, rs5918) polymorphism were multiplexed to be used in a single cell protocol, and single blastomeres were analyzed. RESULTS: In one preimplantation genetic diagnosis cycle, out of 28 retrieved oocytes, 24 embryos fertilized and 12 underwent biopsy. Three embryos were found to be antihuman platelet antigen-1b/1b homozygotes and two were transferred. This cycle resulted in an uneventful pregnancy and birth of a healthy child. CONCLUSION: In cases in which there is antihuman platelet antigen incompatibility and IVIG cannot be administered, preimplantation genetic diagnosis is a reliable alternative to enable birth of unaffected children.