Hemophilia A (HA) is a rare congenital bleeding disorder characterized by coagulation factor VIII deficiency. In severe HA, defined as plasma FVIII clotting activity < 1%, bleeding may frequently occur spontaneously, most commonly in joints, leading to painful hemophilic arthropathy and loss of joint function. Patients with moderate or mild hemophilia A, defined as FVIII clotting activity between 1-<5% and 5-40% respectively, are less likely to have spontaneous bleeding however can have significant bleeding with trauma or surgery. Perioperative management by a hematologist who specializes in hemophilia is needed to ensure hemostasis during surgery. Hemophilia is an X-linked recessive disorder affecting 1 in 5000 to 10,000 males.

A questionnaire to elucidate the dosing, frequency and indication for the use of emicizumab in patients with Hemophilia A (mild, moderate or severe) ages 0-3 years has been developed. Data on any pre-, peri and post-surgical practices while on emicizumab is being collected. Pediatricians are being asked if there are plans to introduce factor 8 to children who are already on emicizumab for primary prophylaxis as well as how and when this is planned on being done. The hope is that this data will help inform understanding of current use of emicizumab in infants and young children as a form of primary prophylaxis, especially when venous access has historically been a limiting factor.

This will be a multi-institutional, retrospective review of pediatric patients ages 0 to 36 months of age who are currently receiving and/or have received emicizumab-kxwh as part of their treatment for hemophilia A with or without inhibitors. Participating sites are part of the New England Region (plus New Jersey and New York-Region II) of hemophilia treatment centers. Each institution will be contributing subjects who have been treated or who are currently being treated with emicizumab, from October 4th, 2018 up to the point of IRB approval. Additionally, each institution will determine the best way to identify eligible patients and keep track of patients enrolled in the study. The Children's Hospital at Montefiore will be the coordinating center.

Inclusion Criteria: Patients must meet the following criteria for study entry:

• Patients who have been prescribed Emicizumab
• Patients who are 0-36 months of age at the time of starting treatment with Emicizumab
• Diagnosis of congenital mild, moderate or severe hemophilia with or without an inhibitor

Exclusion Criteria:

• Patients with acquired Hemophilia A
• Patients with Hemophilia A and another congenital or acquired bleeding disorder.

Patients 0 to 36 months of age, diagnosed with severe, moderate or mild Hemophlia A at the time of initiating treatment with Emicizumab.