The loss of function mutation results in a phenotype that is different from that of a gain of function mutation, and these phenotypes are associated with two different forms of type 4 hemochromatosis. Loss-of-function mutations are more frequent and are associated with type 4A hemochromatosis. These mutations lead to a defect in the localization of ferroportin. Gain-of-function mutations are associated with type 4B and lead to production of ferroportin that resists negative regulation by hepcidin.Unlike other forms of hemochromatosis, which have a recessive pattern of inheritance, type 4 is an autosomal dominant disorder. The dominant inheritance pattern occurs in hemochromatosis type 4 because ferroportin is multimeric. Consequently, mutant ferroportin can associate with wild-type ferroportin in multimers and interfere with the function of normal ferroportin proteins. Pathophysiology
In normal iron regulation, iron is absorbed in the intestine, and ferroportin transports iron from the cells of the intestinal lining into the bloodstream. Iron in the bloodstream is then bound by transferrin, which carries the iron to target cells. Iron is stored in cells and blood serum in a protein called ferritin. Reticuloendothelial macrophages, which can phagocytose red blood cells, are important in the iron recycling process. Ferroportin is upregulated in the reticuloendothelial macrophages after phagocytosis occurs so that iron from the degraded red blood cells can be released into the bloodstream and transported to other types of cells as needed. Hepcidin, a protein synthesized in the liver in response to iron or inflammation, is a regulator of ferroportin expression.
Common noninfectious tenosynovitis are: stenosing tenosynovitis, intersection syndrome, extensor pollicis longus (EPL) tenosynovitis, de Quervains and fourth compartment tenosynovitis. Diagnosis
Diagnosis of tenosynovitis is typically made clinically after a thorough patient history and physical exam. Aspirated fluid can also be cultured to identify the infectious organism. X-rays are typically unremarkable but can help rule out a broken bone or a foreign body

Treatment
The mainstay of treatment for infectious tenosynovitis includes symptom relief, antibiotic therapy, and surgery. Early recognition of the disease with early initiation of antibiotics are important for better range of movement of the affected finger. Minimally invasive procedures into the flexor tendon sheath such as catheter irrigation give better outcomes (74% chance of good outcome) when compared to open surgery (26% chance of good outcome). However, wound irrigation with antibiotics has no clear benefits. Most infectious tenosynovitis cases should be managed with tendon sheath irrigation and drainage, with or without debridement of surrounding necrotic tissue, along with treatment with broad-spectrum antibiotics. In severe cases, amputation may even be necessary to prevent the further spread of infection. Following surgical intervention, antibiotic therapy is continued and adjusted based on the results of the fluid culture. Prognosis
The earlier the condition is identified, the better the chance of getting full range of motion of the finger. However, finger stiffness, Boutonniere deformity, deep space infection, tendon necrosis, adhesions, persistent infection, and need for amputation of the finger can occur. Tendon adhesion and finger stiffness are caused by the violation of the flexor tendon sheath.