Factor IX (or Christmas factor) (EC 3.4.21.22) is one of the serine proteases of the coagulation system; it belongs to peptidase family S1. Deficiency of this protein causes haemophilia B. It was discovered in 1952 after a young boy named Stephen Christmas was found to be lacking this exact factor, leading to haemophilia.Coagulation factor IX is on the World Health Organizations List of Essential Medicines. Physiology
Factor IX is produced as a zymogen, an inactive precursor. It is processed to remove the signal peptide, glycosylated and then cleaved by factor XIa (of the contact pathway) or factor VIIa (of the tissue factor pathway) to produce a two-chain form, where the chains are linked by a disulfide bridge. When activated into factor IXa, in the presence of Ca2+, membrane phospholipids, and a Factor VIII cofactor, it hydrolyses one arginine-isoleucine bond in factor X to form factor Xa. Factor IX is inhibited by antithrombin.Factor IX expression increases with age in humans and mice. In mouse models, mutations within the promoter region of factor IX have an age-dependent phenotype. Domain architecture
Factors VII, IX, and X all play key roles in blood coagulation and also share a common domain architecture. The factor IX protein is composed of four protein domains: the Gla domain, two tandem copies of the EGF domain and a C-terminal trypsin-like peptidase domain which carries out the catalytic cleavage. The N-terminal EGF domain has been shown to at least in part be responsible for binding tissue factor. Wilkinson et al.
Diagnosis
The cystic nature of a breast lump can be confirmed by ultrasound examination, aspiration (removal of contents with needle), or mammogram. Ultrasound can also show if the cyst contains solid nodules, a sign that the lesion may be pre-cancerous or cancerous. Examination by a cytopathologist of the fluid aspirated from the cyst may also help with this diagnosis. In particular, it should be sent to a laboratory for testing if it is blood-stained. Commonly, cysts are detected with the help of mammograms. However, the medical history and physical examination also play an important role in establishing an accurate diagnosis. During these tests, the doctor will try to find out as much information as possible regarding the symptoms the patient has experienced, their intensity and duration and the physical examination is performed regularly to check for other abnormalities that may exist within the breast. As mentioned above, cysts are often undetectable at touch. Therefore, a mammogram can provide valuable and clear images of the breast tissue. Generally, if there is any abnormality within the breast tissue, it will be shown on the mammogram. There are two types of mammograms available. One of them is primarily used in screening, and are ordered for patients who do not show any symptoms and these are called screening mammograms. Diagnostic mammograms are used on patients who developed certain symptoms of a breast condition or in patients whose screening mammograms showed abnormalities. Patients suspected of breast cysts will normally be given a diagnosing mammogram, although they are not suspected of cancer.