Neonatal alloimmune thrombocytopenia
Encyclopedia
Neonatal Alloimmune Thrombocytopenia
(NAITP or NAIT or NAT for short; or fetal and neonatal alloimmune thrombocytopenia, FNAIT, feto-maternal alloimmune thrombocytopenia, FMAITP or FMAIT) is a disease
that affects fetus
es and newborns. Genetic differences between the fetus and mother may result in the expression of certain antigens by fetal platelet
s, not expressed by the mother. Fetomaternal transfusions result 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.
(IVIG) during pregnancy and immediately after birth has been shown to help reduce or alleviate the effects of NAIT in infants and reduce the severity of thrombocytopenia. The most common treatment is weekly IVIG infusions at a dosage of 1g/kg beginning at 16 to 28 weeks of pregnancy, depending on the severity of the disease in the previous affected child, and continuing until the birth of the child. In some cases this dosage is increased to 2g/kg and/or combined with a regiment of prednisone depending on the exact circumstances of the case. Although this treatment has not been shown to be effective in all cases it has been shown to reduce the severity of thrombocytopenia in some. Also it is suspected that (though not understood why) IVIG provides some added protection from ICH (intercranial hemorrhage) to the fetus.
There is a support group for those with this condition
NAIT Homepage
Thrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...
(NAITP or NAIT or NAT for short; or fetal and neonatal alloimmune thrombocytopenia, FNAIT, feto-maternal alloimmune thrombocytopenia, FMAITP or FMAIT) is a disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
that affects fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
es and newborns. Genetic differences between the fetus and mother may result in the expression of certain antigens by fetal platelet
Platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days...
s, not expressed by the mother. Fetomaternal transfusions result 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
Human leukocyte antigen
The human leukocyte antigen system is the name of the major histocompatibility complex in humans. The super locus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encodes cell-surface antigen-presenting proteins and...
(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.
Signs and Symptoms
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.Diagnosis
Although there are currently no widespread tests for NAIT, platelet antigen genotyping and platelet antibody identification can be performed on the maternal and paternal blood to determine the exact nature of the incompatibility.Causes
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. Unlike the hemolytic disease, NAIT occurs during the first pregnancy in up to 50% of cases, and the affected fetuses may develop severe thrombocytopenia (<50,000 /μL) very early during pregnancy. Usually, the thrombocytopenia increases as gestation progresses. In utero intracranial hemorrhage occurs in about 10% of affected cases. This complication may also take place before 20 weeks of gestation. The recurrence of NAIT been estimated to be more than 80% in subsequent pregnancies with incompatible fetuses.During Pregnancy
The use of Intravenous immunoglobulinIntravenous immunoglobulin
Intravenous immunoglobulin is a blood product administered intravenously. It contains the pooled IgG extracted from the plasma of over one thousand blood donors. IVIG's effects last between 2 weeks and 3 months...
(IVIG) during pregnancy and immediately after birth has been shown to help reduce or alleviate the effects of NAIT in infants and reduce the severity of thrombocytopenia. The most common treatment is weekly IVIG infusions at a dosage of 1g/kg beginning at 16 to 28 weeks of pregnancy, depending on the severity of the disease in the previous affected child, and continuing until the birth of the child. In some cases this dosage is increased to 2g/kg and/or combined with a regiment of prednisone depending on the exact circumstances of the case. Although this treatment has not been shown to be effective in all cases it has been shown to reduce the severity of thrombocytopenia in some. Also it is suspected that (though not understood why) IVIG provides some added protection from ICH (intercranial hemorrhage) to the fetus.
After Birth
The most rapidly effective treatment in infants with severe hemorrhage and/or severe thrombocytopenia (<30x109/L) is the transfusion of compatible platelets (i.e. platelets from a donor who, like the mother lacks the causative antigen). Additionally if the thrombocytopenia in the infant at birth is not severe enough to warrant a transfusion of platelets (>30x109/L) an infusion of IVIG (1g/kg/day for two days) in the infant has been shown to rapidly increase platelet count and reduce the risk of related injury.External links
- http://www.gpnotebook.co.uk/simplepage.cfm?ID=812318744
- http://www.adhb.govt.nz/newborn/Guidelines/Blood/Platelets/NAIT.htm
- Dr. Joanne Kwak-Kim (Past President American Society for Reproductive Immunology): http://www.rosalindfranklin.edu/DNN/RFUHS/PhysicanDirectory/tabid/2654/Default.aspx#Reproductive
- http://www.cornellphysicians.com/jamesbussel/
- http://www.noich.org
- http://www.nait-fait/info in english, german and turkish for patients and doctors. Text, fotos, TV-film on family with 4 fait-children
There is a support group for those with this condition
- http://health.groups.yahoo.com/group/NAIT/
NAIT Homepage
- http://www.naitbabies.org