Von Willebrand disease

Ajouté : 2026-05-19

[00:00:02]Von willilibbrand disease, named after Finnish doctor Eric Adolf von Willilibrand, who first described the condition, is a bleeding condition associated with either a low amount or poor quality of vonilibbrand factor.

[00:00:20]Imagine you're repotting a cactus and a spine pricks you, damaging the tiny blood vessels in your fingertip. As a result, the body triggers primary hemostasis, which is a well-coordinated process that stops bleeding.

[00:00:35]This injury exposes the collagen in the blood vessel wall, which is rich in vonilibbrand factor and triggers local endothelial cells to release more vonwillibbrand factor into circulation.

[00:00:49]Once released, the von willilibbrand factor sticks to the damaged area and acts like glue, providing a foundation for platelet attachment. Circulating platelets use their glyoprotein 2B receptors to bind this glue-like substance, triggering their activation.

[00:01:06]They change shape and extend tentacle-like arms to grab onto nearby platelets. Once activated, they release more vonilibbrand factor along with serotonin and calcium. Enjoying our Osmosis videos?

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[00:01:37]Platelets also release adenosine diphosphate and thromboxane A2 which together activate other platelets that haven't bound the vonilibbrand factor.

[00:01:48]These two substances also spark platelets to express new surface proteins called GP2B/3A.

[00:01:56]Acting like hooks, these proteins enable platelets to catch fibbrronogen, which acts like a pair of handcuffs, linking two platelets together. Eventually, this results in a snowball effect with more platelets piling up, creating a plug that seals the injury.

[00:02:15]Once the body creates the platelet plug, it triggers secondary hemostasis to reinforce the clot with a strong fibbrin mesh. This process involves the exttrinsic and intrinsic coagulation pathways which ultimately converge into the common coagulation pathway.

[00:02:36]In the exttrinsic pathway, blood vessel injury exposes factor 3, also known as tissue factor, which activates factor 7.

[00:02:45]Next, activated tissue factor, activated factor 7, and calcium come together to activate factor 10, eventually triggering the common pathway.

[00:02:57]Activated factor 10 joins forces with factor 5 and calcium to form the proth thrombinase complex which converts factor 2 called proth thrombin into activated factor 2 called thrombin.

[00:03:12]Next thrombin converts factor 1 known as fibbrinogen into activated factor 1 called fibbrin. Finally, thrombin activates factor 13 which binds calcium to create fibbrin cross links to stabilize the clot.

[00:03:30]On the flip side, the intrinsic pathway begins when collagen of the blood vessel wall activates factor 12, also known as the hgamin factor. Activated factor 12 activates factor 11, which with the help of calcium activates factor 9.

[00:03:50]Next, let's focus on factor 8, which circulates through the bloodstream bound to the vonulibbrand factor. Think of the vonilibbrand factor as a protective shield guarding factor 8 from proteins C and S, which would otherwise break it down. Now, during secondary hemostasis, thrombin releases factor 8 from the vonilibbrand factor and activates it.

[00:04:13]together activated factor 8, activated factor 9 and calcium form a complex which activates factor 10 and triggers the common pathway.

[00:04:26]Now in von willilibbrand disease there isn't enough functional vonilibbrand factor to help platelets stick to the site of injury or carry factor 8. As a result the body struggles to stop bleeding. In most cases, von willilibbrand disease is inherited and caused by mutations in the vonilibbrand gene. But not all inherited forms are the same. That's why the condition is subdivided into three main types.

[00:04:55]The most common type is type one, an autotoal dominant condition where a mutation in just one alil results in insufficient production and lowers circulatory levels of the vonilibbrand factor. In other words, these individuals have a partial quantitative defect.

[00:05:15]Type two is a bit more complex and covers several different subtypes including 2 A, 2 B, 2 M, and 2N. The first three follow an autotosomal dominant inheritance pattern, while type 2N follows an autotosomal recessive pattern, meaning both alals must be affected for the condition to appear.

[00:05:37]Regardless of the subtype, all type two forms result in a qualitative defect where the body produces enough vonwillibbrand factor but the protein doesn't function properly.

[00:05:50]Now in type 2 A and 2 M, the von willilibbrand factor attaches well to subendothelial collagen and factor 8, but is unable to bind platelets. So in this case, it's like having expired glue that can't properly stick platelets to the damaged area. On the other hand, in type 2B, the von willilibbrand factor is way too sticky, causing platelets to clump together in the bloodstream even without injury.

[00:06:19]Next, in type 2N, the vonilibbrand factor binds well to the subendothelial collagen and platelets, but binds poorly to factor 8. As a result, factor 8 is unprotected and broken down by protein C and S leading to low factor 8 levels.

[00:06:40]Finally, type three follows an autotosomal recessive inheritance pattern and involves a severe quantitative defect of the vonilibbrand factor. In this case, von willilibbrand factor levels are extremely low which results in impaired platelet aggregation and severely low factor 8 levels.

[00:07:01]Although most cases are inherited, some people can develop acquired vonilibbrand disease. In these cases, certain acquired conditions can interfere with the function of the vonilibbrand factor.

[00:07:13]For example, in autoimmune disorders like systemic lupus, the body produces antibodies that target self-p proteins including vonilibbrand factor leading to its destruction.

[00:07:28]Now clinical manifestations depend on the type. Individuals with type 1, type 2 A, 2B, and 2M could be asymptomatic or present with mild mucoutaneous bleeding such as gum bleeds. Also, they might report easy bruising, excessive bleeding from wounds, and heavy menration.

[00:07:52]Most commonly, they're unaware of the condition until some surgical or dental intervention reveals the bleeding issues. However, clinical manifestations can become severe if they begin taking medications that can impair the body's ability to form clots. These include anti-coagulants and antiplatlet medications.

[00:08:14]On the flip side, individuals with type 2 N and type 3 have severe bleeding manifestations including joint and muscle bleeds along with gastrointestinal hemorrhage. Finally, acquired vonilibbrand disease causes new bleeding symptoms that develop alongside certain underlying conditions like autoimmune diseases.

[00:08:37]Moving on to diagnosis, which primarily relies on labs, a complete blood count typically reveals a normal platelet count. However, in type 2B, the extremely sticky von willilibbrand factor will clump platelets together causing thrombocytoenia.

[00:08:55]Next, the coagulation profile can help you assess the secondary hemostasis and coagulation pathways.

[00:09:02]Prothroen time or PT evaluates factors of the exttrinsic and common pathways while activated partial thromboplastin time or apt reflects factors of intrinsic and common pathways. Finally, thromben time or TT measures how long it takes for fibbrronogen to turn into fibbrin in the presence of thrombin. In von willilibbrand disease, PT is typically normal because the extrinsic pathway remains unaffected. Next, the apt which relies on factor 8 can be normal or prolonged. In type one, apt remains normal because there's only a partial quantitative deficiency.

[00:09:47]Although factor 8 has less protection from the vonilibbrand factor, proteins C and S don't break it down enough to disrupt the coagulation cascade.

[00:09:57]However, in types 2 and three, apt is prolonged because this protection is compromised, allowing proteins C and S to break down factor 8, significantly lowering its levels and prolonging APTT.

[00:10:13]In all types, thromben time is typically normal since there's no impairment of fibbrinogen to fibbrin conversion.

[00:10:22]Finally, let's focus on specific tests used in the diagnosis of vonilibbrand disease. Von willilibbrand factor antigen assay measures the amount of this protein in the blood. Low levels can be suggestive of the condition.

[00:10:37]Next, there's the rristtocetan co-actor activity test. When you add rristtoetin to a blood sample containing normal von willilibbrand factor, it activates the protein to clump platelets together resulting in visible coagulation.

[00:10:52]However, no clumping indicates reduced activity suggesting von willilibbrand disease.

[00:10:59]Lastly, factor 8 activity measures how well this factor works. Although it can sometimes be normal, it's usually decreased because protein C and S break it down.

[00:11:13]For managing bleeding episodes in types one and two, the first choice treatment is desmopressin, a vasopressin analog.

[00:11:20]It stimulates endothelial cells and meggaariotes to release stored vonilibbrand factor boosting its levels in the blood and helping with blood clotting. However, you should avoid desmopressin in type 2b because the vonilibbrand factor is overly sticky.

[00:11:37]Boosting its levels can induce platelet clumping leading to severe thrombocytoenia eventually worsening the bleeding.

[00:11:45]Finally in type three treatment relies on intravenous infusion of vonilibbrand factor concentrate often combined with factor 8.

[00:11:57]All right as a quick recap in vonilibbrand disease there isn't enough functional vonilibbrand factor to do its job. First, it fails to help platelets stick to the sight of injury. Second, it can't carry factor 8. Inherited vonilibbrand disease includes three types. In type one, a person has reduced levels of the factor. Type two involves a dysfunctional form and in type three there is a severe deficiency. On the flip side, acquired forms can occur due to autoimmune conditions like systemic lupus.

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