What's hemophilia A?
Hemophilia A is an inherited bleeding disorder caused by a shortage of clotting factor VIII, a protein the blood needs to form a stable clot. Because the factor VIII gene sits on the X chromosome, it almost always affects boys and men, while women are usually carriers. Without enough factor VIII, bleeding lasts longer than normal, especially into joints and muscles.
| Also indexed as | OMIM:306700, MONDO:0010602 |
|---|---|
| Features mapped | 9 |
| Treatments mapped | 12 |
| Published sources | 13 |
| Last reviewed | 2026-08-04 |
Signs and symptoms
X-linked recessive inheritance
Hemophilia A is inherited in an X-linked recessive pattern. Mothers who carry the change have a 1 in 2 chance of passing it to each son (who would be affected) and to each daughter (who would be a carrier). Genetic counselling helps families understand their specific risks.
Joint hemorrhage
Bleeding into joints (hemarthrosis), especially knees, ankles, and elbows, is the most characteristic problem. Repeated joint bleeds can damage the joint over time, which is why preventing bleeds with regular treatment matters so much.
Persistent bleeding after trauma
Because the blood cannot clot normally, even minor cuts, dental work, or surgery can lead to prolonged bleeding in hemophilia A. Bleeding that does not stop after events like circumcision is sometimes the first clue to the diagnosis.
Prolonged partial thromboplastin time
A clotting blood test called the aPTT is prolonged, while other clotting tests are usually normal. This pattern is an early clue that points toward a factor VIII or IX problem and prompts specific factor testing.
Reduced factor VIII activity
A low level of working factor VIII in the blood is the defining laboratory finding. The exact level sorts the condition into mild, moderate, or severe, which guides how intensively it is treated.
Muscle hemorrhage
in hemophilia A, a deficiency of a clotting factor, bleeding tends to be delayed and to occur deep inside the body, including into the muscles and joints.
Osteoarthritis
Repeated bleeding into the joints can lead to hemophilic arthropathy, a destructive joint disease causing limited movement and chronic pain in hemophilia A.
Hemarthrosis
Bleeding into the joints (hemarthrosis), most often the ankles, knees, and elbows, is the hallmark bleeding problem of hemophilia A; repeated episodes can damage the joint over time.
Intracranial hemorrhage
Bleeding into or around the brain (intracranial hemorrhage) is the most serious complication of hemophilia A. It is especially dangerous in babies and young children, where it can be life-threatening or leave lasting neurological damage, which is a key reason clotting-factor prophylaxis is often started early.
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
factor VIII replacement
The long-standing treatment is replacing the missing clotting factor with factor VIII infusions, given to stop a bleed or, as regular prophylaxis, to prevent bleeds. Modern longer-acting products reduce how often infusions are needed. Some people develop antibodies (inhibitors) against infused factor VIII, which changes the treatment approach.
Used to help with: Hemophilia A.
“…treated with FVIII…”
emicizumab
Emicizumab is a newer medicine given as an injection under the skin, as infrequently as weekly to monthly. It mimics the job of factor VIII to prevent bleeds and works even in people who have developed inhibitors against factor VIII. It is used for prevention, not to treat a bleed that is already happening.
Used to help with: Hemophilia A.
“…more recently, Emicizumab…”
desmopressin
desmopressin, a synthetic hormone that raises the body's own levels of von Willebrand factor and factor VIII, is used in the treatment of mild hemophilia A.
Used to help with: Hemophilia A.
“Its haemostatic potential was later recognized when it was observed to enhance endogenous levels of vWF and factor VIII, leading to its incorporation into the treatment of mild haemophilia A and von Willebrand disease (vWD).”
AAV gene therapy
adeno-associated virus (AAV) vector-mediated gene therapy is being developed as a one-time treatment aimed at long-term disease control in hemophilia.
Used to help with: Hemophilia A.
“More recently, gene and RNA-based therapies are further transforming both diseases toward curative attempts: in hemophilia, adeno-associated virus vector-mediated gene therapy and lentiviral stem-cell approaches; in HAE, antisense oligonucleotide-mediated kallikrein suppression.”
efanesoctocog alfa
efanesoctocog alfa is an ultra-extended half-life factor VIII concentrate used to treat and prevent bleeding in hemophilia A.
Used to help with: Hemophilia A.
“Efanesoctocog alfa is a novel, 'ultra-extended half-life' FVIII concentrate for bleed treatment and prevention in haemophilia A.”
prophylaxis
Prophylaxis means giving treatment on a regular schedule to prevent bleeds before they happen, rather than only treating bleeds after they start. For people with severe hemophilia a, and for those with moderate disease who bleed easily, it is recommended as early as possible, ideally before the first joint bleed, with the aim of preventing future bleeds and protecting the joints over the long term.
Used to help with: Hemophilia A.
“Prophylaxis is recommended as early as possible in children with severe hemophilia and in those with moderate disease and a severe bleeding phenotype, ideally before the first joint bleed, to prevent future bleeds and microbleeds and to therefore preserve joint health.”
fitusiran
Fitusiran is one of the newer non-factor medicines used to prevent bleeds in hemophilia a. In trials it likely reduced the yearly bleeding rate compared with treating bleeds only as they occurred. It is given to prevent bleeds rather than to stop a bleed that has already started.
Used to help with: Hemophilia A.
“Fitusiran also likely reduced ABR for all…”
concizumab
Concizumab is another non-factor medicine studied for preventing bleeds in hemophilia a. In trials it may reduce the yearly rate of bleeds compared with treating each bleed only after it begins. Like other preventive medicines, it is used to lower how often bleeds happen.
Used to help with: Hemophilia A.
“Concizumab may reduce ABR for all…”
immune tolerance induction
Some people with severe hemophilia a develop inhibitors, which are antibodies that block factor VIII treatment from working. Immune tolerance induction (ITI) is an approach that aims to retrain the body to accept factor VIII so that inhibitors are eradicated over the long term. In children with high-titer inhibitors it has been compared with emicizumab prophylaxis, which instead focuses on immediate bleed control.
Used to help with: Hemophilia A.
“EMI prophylaxis was associated with improved bleeding control and QoL while reduced costs compared with ITI, offering a valuable option for SHAcwHTI, prioritizing immediate hemostasis over the long-term goal of inhibitor eradication, especially in resource-limited settings.”
bypassing agents
When a person with hemophilia a has developed inhibitors, ordinary factor VIII may no longer stop a bleed. Bypassing agents are treatments that help the blood clot by working around the missing factor, and they are used for bleeds that break through prevention and around surgery. At higher doses they can raise the risk of an unwanted clot (thrombosis), so the amount used is balanced carefully.
Used to help with: Hemophilia A.
“…breakthrough bleeding and perioperative management still require additional bypassing agents, which increases the risk of thrombosis in these…”
marstacimab
Marstacimab is one of the newer non-factor medicines for hemophilia a. These medicines are used for prophylaxis only, meaning they are taken on a schedule to prevent bleeds; a separate factor or bypassing treatment is still needed to control a bleed that has already started or to cover surgery.
Used to help with: Hemophilia A.
“For nonfactor therapies-including emicizumab, concizumab, marstacimab and fitusiran-critical considerations for bleed management, surgical procedures, and transitioning between products, emphasizing that these agents are for prophylaxis only and require specific, often product-specific, concomitant factor or bypassing agent protocols for acute haemostasis.”
tranexamic acid
Tranexamic acid is an antifibrinolytic medicine that helps hold blood clots together by slowing their breakdown. In hemophilia A it is used as an add-on to reduce bleeding; for example, in people with hemophilia undergoing major joint (hip) surgery it has been shown to reduce blood loss around the operation.
Used to help with: Hemophilia A.
“Tranexamic acid (TXA), an efficient antifibrinolytic agent, may benefit the outcomes of THA for patients with hemophilia (PWH).”
What changes how it shows up
Carrying the genetic change is not the whole story. The factors below are described in the research mapped here as changing whether, or how strongly, the condition appears. They modulate how the genotype is expressed; they do not, on their own, cause or cure it.
factor VIII inhibitor development
some people with hemophilia A develop inhibitors (antibodies against factor VIII), and the risk of inhibitor development is one of the factors that shapes which treatment is chosen.
Described as modulating: Hemophilia A.
“The choice of therapy (nonfactor replacement therapy, factor concentrate) should be individualized on the basis of the type and severity of hemophilia, patient age, venous access, risk of inhibitor development, clinical presentation, and family circumstances.”
severity by factor VIII activity level
Hemophilia A is graded by how much working factor VIII is in the blood. Severe disease means very low factor VIII activity (under about 1% of normal) and tends to cause spontaneous bleeding; moderate disease (roughly 1 to 5%) causes milder spontaneous and injury-related bleeds; mild disease (higher residual activity) usually bleeds only after surgery or significant trauma. The level largely predicts how often and how easily a person bleeds.
Described as modulating: Hemophilia A.
“The classification of factor VIII deficiency, generally used based on plasma levels of factor VIII, consists of severe (<1% normal factor VIII activity), moderate (1% to 4% factor VIII activity), or mild (5% to 25% factor VIII activity).”
How to read the evidence labels
Where this comes from
This guide is built from 13 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.
Take it further
Printed, source-linked documents built from this condition's graph — ready to bring to an appointment or attach to a coverage request. Every claim carries its published source, the same as this guide.