Abstract: Objective To observe the phenotypic heterogeneity of severe hemophilia A in China and investigate the clinical
factors for defining the severity of the clinical presentations. Methods The data including the age of first bleeding and first
joint bleeding, bleeding frequency, the number of joint deformities and body mass index (BMI) were collected from 223
patients with severe hemophilia A (FVIII:C≤2%). Results The median age at first bleeding was 1 year (range: 0-35 years). The
percentages of patients with first bleeding age<1 year, ≥2 years and ≥6 years were 44.3% (94/212), 34.4% (73/212), and 10.8%
(23/212), respectively. The median age at first joint bleeding was 2.25 years. The percentages of patients with first joint bleeding
age ≤1 year, ≥2 years and ≥6 years were 25.5% (24/94), 57.4% (54/94), and 18.1% (17/94), respectively. The percentage of
patients who did not have joint bleeding was 7.4% (7/94). The median annual bleeding frequency was 24 per year (range:
1-120), and the proportion of patients with annual bleeding episodes of less than 6 times was 12.9%. Only 24.7% of the patients
were free of any joint deformities. Analysis showed that milder cases had older ages of first bleeding and first joint bleeding
than the severe cases, and the milder cases had also significantly lower BMI. Conclusion The age of first bleeding and first
joint bleeding and BMI may predict the clinical severity of hemophilia Ain China in the early stage.