A study recently published in Vox Sanguinis analyzed the distribution of human platelet antigen (HPA) types in the Saudi population, finding that genetic data does not always accurately predict the risk of fetal and neonatal alloimmune thrombocytopenia (FNAIT).
“This divergence highlights the complexity of sensitization processes and the clinical relevance of formed alloantibodies,” the authors explained. “These discrepancies remain poorly understood.”
What is FNAIT?
Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare but serious condition that affects 0.1% of pregnancies in which a pregnant mother’s immune system produces antibodies against the platelets of her fetus. This occurs when a fetus inherits platelet antigens from the father that are not compatible with the mother, typically involving a protein called human platelet antigen (HPA). The mother’s immune system recognizes the fetal platelets as foreign, attacking and destroying them, leading to low platelet levels (thrombocytopenia) in the fetus or newborn.
The study collected blood samples from 118 adults living in various regions of Saudi Arabia. Genetic analysis was conducted on HPA systems one through 11 and 15. Although HPA-6 to 11 are not typically associated with medical conditions, they were included to explore the possibility of them causing clinical syndromes in rare cases.
Read more about FNAIT causes and risk factors
Results showed that HPA-1, -2, -3, -5, -9 and -15 were all polymorphic. This means that multiple variants of each gene were identified in the study population. Notably, the distribution of HPA-5 variants was different than expected. Given that HPA-5b is often implicated in FNAIT, this finding requires further analysis, the authors stated.
Statistical analysis predicted that the risk of HPA mismatch ranged from 0.01% to 11.72% for blood transfusions and 0.0% to 7.42% for pregnancy, depending on an individual’s genetic background.
Even though the mismatch data did not fully predict clinical outcomes, this data may serve as a valuable tool for future research on pregnancy, transfusion medicine, and population genetics.
The investigators also combined their data with genetic information from other populations to examine patterns in HPA distribution. They identified four clusters based on HPA data: Arab populations, African populations, Euro-American populations and Polynesian, East and Southeast Asian populations.
In the future, population-specific genetic mapping could be utilized to help mitigate the risk of alloimmunization as a result of transfusions or pregnancy. “The geographic structuring of HPA polymorphisms highlighted in this study underscores the need for regional donor registries,” the researchers concluded.
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