Neonatal alloimmune thrombocytopenia
| Fetal and Neonatal Alloimmune Thrombocytopenia | |
|---|---|
| Synonyms | fetal and neonatal alloimmune thrombocytopenia (FNAIT), feto-maternal alloimmune thrombocytopenia (FMAITP, FMAIT) |
| Classification and external resources | |
| Specialty | pediatrics |
| ICD-10 | P61.0 |
| ICD-9-CM | 776.1 |
| DiseasesDB | 33767 |
| eMedicine | med/3256 med/3480 |
Neonatal alloimmune thrombocytopenia (NAITP, NAIT, NATP or NAT) is a disease that affects babies in which the platelet count is decreased. Platelet antigens are inherited from both mother and father. NAIT is caused by antibodies specific for platelet antigens inherited from the father but which are absent in the mother. Fetomaternal transfusions (or fetomaternal hemorrhage) results in the recognition of these antigens by the mother's immune system as non-self, with the subsequent generation of allo-reactive antibodies which cross the placenta. NAIT, hence, is caused by transplacental passage of maternal platelet-specific alloantibody and rarely human leukocyte antigen (HLA) allo-antibodies (which are expressed by platelets) to fetuses whose platelets express the corresponding antigens. NAIT occurs in somewhere between 1/800 and 1/5000 live births. More recent studies of NAIT seem to indicate that it occurs in around 1/600 live births in the Caucasian population.
Frequently, the thrombocytopenia is mild and the affected neonates remain largely asymptomatic. In these cases, therapeutic interventions are not indicated. In case of severe thrombocytopenia, the neonates may exhibit hemorrhagic complication at or a few hours after delivery. The most serious complication is intracranial hemorrhage, leading to death in approximately 10% or neurologic sequelae in 20% of cases.
About 80% of cases of NAIT are caused by antibodies against platelet antigen HPA-1a, 15% by anti-HPA-5b, and 5% by other antibodies (e.g. HPA-1b, HPA-15, HPA-3 and HPA-9b).HPA-1a is present in 98% of the population of the United States, suggesting that approximately 2% of women who are HPA-1a negative may be at risk for NAIT during pregnancy. Of course, the antigen expression of the father must also be taken into account—in most cases the father is HPA-1a/1a or 1a/1b and the mother is HPA-1b/1b with anti-HPA-1a antibodies. In Asians, HPA-4 antigens are the most frequently implicated.
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