An overlap syndrome is a medical condition which shares features of at least two more widely recognised disorders. Examples of overlap syndromes can be found in many medical specialties such as overlapping connective tissue disorders in rheumatology, and overlapping genetic disorders in cardiology. Rheumatology
Examples of overlap syndromes in rheumatology include mixed connective tissue disease and scleromyositis. Diagnosis depends on which diseases the patient shows symptoms and has positive antibodies for in their lab serology. In overlap syndrome, features of the following diseases are found (most common listed):
Systemic lupus erythematosus (SLE)
Systemic sclerosis
Polymyositis
Dermatomyositis
Rheumatoid arthritis (RA)
Sjögrens syndrome
Eosinophilic granulomatosis with polyangiitis (EGPA)
Autoimmune thyroiditis
Antiphospholipid antibody syndromeThe treatment of overlapping connective tissue disorders is mainly based on the use of corticosteroids and immunosuppressants. Biologic drugs, i.e. anti-TNFα or anti-CD20 monoclonal antibodies, have been recently introduced as alternative treatments in refractory cases. There are some concerns with the use of anti-TNF agents in patients with systemic autoimmune diseases due to the risk of triggering disease exacerbations.The term polyangiitis overlap syndrome refers to a systemic vasculitis that shares features with two or more distinct vasculitis syndromes. The most common type of polyangiitis overlap syndrome is microscopic polyangiitis (MPA), which shares features with EGPA, granulomatosis with polyangiitis and panarteritis nodosa. Sometimes polyangiitis overlap syndrome is used as a synonym for MPA. Gastroenterology
In gastroenterology, the term overlap syndrome may be used to describe autoimmune liver diseases that combine characteristic features of autoimmune hepatitis, primary biliary cirrhosis and primary sclerosing cholangitis.
While cardiomyopathy can be life-threatening, it is commonly resolved or substantially improved in Barth Syndrome patients after puberty.Neutropenia, a granulocyte disorder that results in a low production of neutrophils, the bodys primary defenders against bacterial infections, is another severe manifestation of Barth Syndrome. In general, lower levels of neutrophils render a patient more vulnerable to bacterial infections; in Barth Syndrome patients, however, there are reports of relatively fewer bacterial infections as compared to non-Barth patients with neutropenia. Cause
The tafazzin gene (TAZ, also called G4.5 or NG_009634) is highly expressed in cardiac and skeletal muscle; its gene product, Taz1p, functions as an acyltransferase in complex lipid metabolism. Any type of mutation of TAZ (missense, nonsense, deletion, frameshift, and/or splicing) is closely associated with Barth syndrome.In 2008, Dr. Kulik found that every patient with Barth Syndrome that he tested had abnormalities in their cardiolipin, a lipid found inside the mitochondria of cells. Cardiolipin is intimately connected with the electron transport chain proteins and the membrane structure of the mitochondrion, the energy-producing organelle of the cell. iPLA2-VIA has been suggested as a target for treatment.The human tafazzin gene is over 10,000 base pairs in length, the full-length mRNA, NM_000116, being 1919 nucleotides long, encoding 11 exons with a predicted protein length of 292 amino acids and a molecular weight of 33.5 kDa. It is located at Xq28; the long arm of the X chromosome. This explains the X-linked nature of Barth Syndrome. There are some case reports of women who are asymptomatic carriers of the TAZ mutation.