, Juraj Payer2 and Manfred Herold3
(1)
National Institute for Rheumatic Diseases, Piestany, Slovakia
(2)
Fifth Department of Internal Medicine, Comenius University University Hospital, Bratislava, Slovakia
(3)
Department of Internal Medicine VI, Medical University of Innsbruck, Innsbruck, Austria
Fab fragment A fragment (part) of the immunoglobulin molecule (usually IgG) able to bind to an antigen. It is formed by its proteolytic degradation and contains one binding site between the variable domains of the light and heavy chains.
F(ab) 2 fragment A double Fab fragment. It contains both binding sites of the original molecule. It is practically an immunoglobulin molecule without the C-terminal halves of the heavy chains that form the Fc fragment.
Fabry’s disease Belongs to the group of sphingolipidoses. It is an inherited X-linked recessive inborn error of the glycosphingolipid metabolism. It occurs due to a deficiency of the enzyme α-galactosidase A which is coded by a gene localised on the long arm of the X chromosome (Xq22). As a consequence of this enzyme defect, a glycolipid known as globotriaosylceramide accumulates in the blood vessels, other tissues and organs.
► Clinical symptoms and signs
Episodes of painful acroparaesthesia
A significant reduction or absence of perspiration (anhidrosis)
Characteristic skin lesions (angiokeratomas)
Ocular changes
Decreased activity of α-galactosidase A
FACS (fluorescence-activated cell sorter) A separator of fluorescence-activated cells (flow cytometer). This device allows the analyses and division of a mixture of cells based on their diverse ability to bind a certain antibody labelled by a fluorescence dye. It is a technique referred to as flow cytometry (cytofluorography). The device has two detectors, one of which separates the cells according to the intensity of their fluorescence and the other one according to their size. Newer cell analysers make it possible to use three different fluorescence labels of cells simultaneously, thereby giving the whole device a higher sorting ability. Using fluorescence-labelled monoclonal antibodies against the differentiation antigen CD4+, it is possible to determine, for example, the T-lymphocyte count in the peripheral blood, using the antibody against CD8, the cytotoxic T-lymphocyte count; using the antibody against CD3, the total T-lymphocyte count, etc.
Factor P – see Properdin.
Familial Mediterranean fever (FMF) A genetically determined autosomal recessive disorder occurring only in certain ethnic groups such as Sephardic Jews, Anatolia Turks and Arabs. The gene, called MEFV, has been localised on chromosome 16. Typically, the onset is in adolescence, usually before the age of 20.
► Clinical symptoms and signs
Recurrent attacks of fever, peritonitis, unilateral pleuritis and arthritis.
Periods of remission are usually asymptomatic.
In untreated patients, type AA amyloidosis may develop.
Regular treatment with colchicine prevents attacks and prevents the development of amyloidosis.
Farber disease A disease belonging to the sphingolipidoses, with musculoskeletal manifestation, characterised by an accumulation of lipids in tissues due to an enzyme deficiency. Farber’s lipogranulomatosis is an autosomal recessive defect caused by a deficiency of ceramidase, an enzyme which cleaves fatty acids from ceramide producing sphingosine. It appears in the neonatal period.
► Clinical symptoms and signs: Red painful xanthomas form around the joints and the peritendons, which leads to the development of joint and tendon contractures. Motor development retardation, macular degeneration and mental retardation are present. Patients die early. The primary cause of death is oedema in the laryngeal region and epiglottis leading to recurrent pulmonary infections. A mild form of this disease allows longer survival, and these children may present to a rheumatologist with their joint problems and mental retardation. There is no curative treatment.
Farnesyl diphosphate synthetase (FPPS) – see Bisphosphonates.
Fas ligand (FasL or CD95L) is a type II transmembrane protein that belongs to the tumour necrosis factor (TNF) family. Its binding with its receptor induces apoptosis. Fas ligand/receptor interactions play an important role in the regulation of the immune system and the progression of cancer.
Fc fragment A crystallisable fragment of the immunoglobulin molecule formed by its proteolytic fragmentation. It represents the C-terminal end of both heavy chains connected by a disulphide bond. It is unable to bind antigen but has other important biological effects, and the most important of which is its ability to bind to Fc-receptors.
Fc-receptors The binding sites for the Fc domains of the immunoglobulin molecules localised on the surface of leukocytes and other cells. Every class of immunoglobulins has its own type of FcR. There are specific Fc-receptors for IgG, IgE, IgM and IgA. The FcR for IgG and IgE can be found in multiple isoforms, usually as high-affinity and low-affinity receptors. They are important in the processes of phagocytosis and antibody-dependent cellular cytotoxicity (ADCC).
Febuxostat A novel, non-purine inhibitor of xanthine oxidase indicated for the treatment of chronic hyperuricaemia (see Allopurinol – Indications for hypouricaemic treatment initiation). Studies have proved that febuxostat has better capability of reducing and maintaining serum uric acid compared to allopurinol. It is also suitable for patients with mild to moderate renal function impairment. Due to its price, it is used as a second-choice medication, when the maximum dose of allopurinol is contraindicated, not tolerated or has insufficient effect. The therapeutic goal is to reach uric acid levels of 360 μmol/l and lower. In European countries, the recommended initial dose of febuxostat is 80 mg/day. In case the effect is not sufficient, it may be increased to 120 mg/day. When initiating the treatment with febuxostat, preventing gout attacks with colchicine (0.5–1 mg/day) for 6 months is recommended. Most common adverse effects are gout attacks, abnormal liver function, diarrhoea, nausea, headache, rash and oedema.
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