Although the majority of hemophilia carriers have a normal bleeding score, a substantial proportion does not, according to a new study published in Haemophilia.

“We believe this analysis contributes significantly to our understanding of bleeding symptoms in hemophilia carriers,” the authors of the study wrote, adding that it also identified the gaps in knowledge that need further analysis. “Further studies designed to elucidate the mechanisms determining the bleeding phenotype are needed.”

Their findings come from the analysis of data from the ATHNdataset, which contains the largest data set of hemophilia carriers in the world. To determine the proportion of hemophilia carriers with a normal bleeding score and factors that affect the bleeding score, John Puetz, MD, and Dunlei Cheng, PhD, searched the dataset for hemophilia carriers with a documented bleeding score.

Continue Reading

They identified 922 hemophilia carriers for analysis. Of these, 74% reported a normal bleeding score, despite 59% having factor activity levels less than 40 IU/dL.

Read more about the etiology of hemophilia

Conversely, 24% of the carriers had a factor activity level of more than 40 IU/dL but reported an abnormal bleeding score.

Using statistical analyses, the researchers identified risk factors for abnormal bleeding scores, including age, clotting factor activity level, ethnicity, and region of residence.

According to the researchers, additional studies are needed to determine why the majority of hemophilia carriers with low factor activity levels report normal bleeding scores while a significant minority of those with normal activity levels report abnormal bleeding scores.

Hemophilia is a bleeding disorder caused by the deficiency of blood clotting factors. The disease is classified as type A or type B depending on which clotting factor is deficient. In hemophilia A, there is a mutation in the gene encoding for factor VIII, while hemophilia B is caused by mutations in the gene encoding for factor IX. Both of these genes are located on the X chromosome.


Puetz J, Cheng D. Descriptive analysis of bleeding symptoms in haemophilia carriers enrolled in the ATHNdataset. Haemophilia. Published online September 29, 2021. doi:10.1111/hae.14422