Researchers in the Netherlands have identified a new platelet antigen that caused fetal and neonatal alloimmune thrombocytopenia (FNAITFetal and neonatal alloimmune thrombocytopenia A rare condition in which a mother’s immune system attacks fetal platelets, leading to dangerously low platelet levels before and/or after birth.) in a newborn boy.
Around the same time, researchers in Germany reported a separate newborn with the same severe bruising and low platelet countPlatelet count A measure of how many platelets are in the blood. FNAIT is characterized by severely reduced counts in a fetus or newborn. and traced it to the very same genetic change. They named the newly recognized marker “Dik.”
FNAIT is a rare condition that occurs when a pregnant woman’s immune system attacks the platelets of her developing baby. Platelets are tiny cell fragments essential for normal blood clotting, and their surfaces carry proteins that vary slightly from one person to the next because of small genetic differences. These variant markers are called human platelet antigens (HPAHuman platelet antigen Proteins found on the surface of platelets. Incompatibility between maternal and fetal human platelet antigens can trigger FNAIT.).
Many are harmless, but when a baby inherits one from the father that the mother does not carry, her immune system may treat it as foreign and produce antibodies against it. More than 40 HPAs have been cataloged so far; HPA-1a causes most cases of FNAIT, while rarer markers account for the others.
Learn more about FNAIT causes and risk factors
In this case, the baby had inherited a tiny genetic change from his father that altered a small part of one of these surface proteins—glycoprotein IIb (GPIIb), part of a receptor that lets platelets clump together to form a clot. The change created a marker that the mother’s immune system had never encountered and therefore reacted to it.
The boy was 4 days old when he arrived at a hospital with severe bruising. Testing showed a severely low platelet count and, although there was no bleeding in the brain—FNAIT’s most dangerous complication—doctors suspected the condition.
Because the same variant had now caused FNAIT in two unrelated families, the researchers concluded that this novel antigen can, on its own, provoke the maternal immune response that drives the FNAIT.
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