Hemophilia A

Inclusion Criteria

- Males aged 12 - 35 years  
 - Severe hemophilia A ( < 1 %  FVIII:C) 
 - No history of Factor VIII inhibitory antibody 
 - For prophylaxis groups, having received at least two prophylactic infusions per week for 45 weeks per year for the prevention of bleeding without relevant  interruption and continuing until the present.  
 - Complete documentation of joints bleeds and their locations prior to start of prophylaxis,  
 - Bleeding history and/or treatments received during the last 5 years documented in the subjects medical records. 
 - For the on-demand subjects > 12 bleeds/year in the  last 5 years. 
 - Written informed consent by subject and parent/legal representative, if < 18 years

Exclusion Criteria

- Individuals with other coagulopathies (e.g., von Willebrand disease) 
 - HIV seropositive subjects 
 - Individuals for whom the most clinically severe joint  is not one of the 4 index joints (ankle, knee)  
 - HCV seropositive individuals who underwent interferon therapy during the last 12 months 
 - Individuals for whom high-magnetic exposure is contraindicated (see section 7.1)
  - Synovectomy performed within the six months prior to investigation enrollment or orthopedic surgery planned to be performed within the investigation  period
 - Joint replacement 
 - For the on-demand treatment group, any period greater than 8 consecutive months having received >/= 50 IU per kg per week Factor VIII for the  prevention of bleeding