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 Rheumatology () is a branch of medicine devoted to the diagnosis and management of disorders whose common feature is inflammation in the bones, muscles, joints, and internal organs. Rheumatology covers more than 100 different complex diseases, c ...

, and overlapping

genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders ...

s in

cardiology Cardiology () is the study of the heart. Cardiology is a branch of medicine that deals with disorders of the heart and the cardiovascular system. The field includes medical diagnosis and treatment of congenital heart defects, coronary artery di ...

Rheumatology

Examples of overlap syndromes in rheumatology include

mixed connective tissue disease Mixed connective tissue disease (MCTD) is a systemic autoimmune disease that shares characteristics with at least two other systemic autoimmune diseases, including Systemic scleroderma, systemic sclerosis (Ssc), systemic lupus erythematosus (SLE),� ...

and

scleromyositis Scleromyositis, is an autoimmune disease (a disease in which the immune system attacks the body). People with scleromyositis have symptoms of both systemic scleroderma and either polymyositis or dermatomyositis, and is therefore considered an ov ...

. Diagnosis depends on which diseases the patient shows symptoms and has positive

antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

for in their lab serology. In overlap syndrome, features of the following diseases are found (most common listed): *

Systemic lupus erythematosus Lupus, formally called systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Common ...

(SLE) *

Systemic sclerosis Systemic scleroderma, or systemic sclerosis, is an autoimmune rheumatic disease characterised by excessive production and accumulation of collagen, called fibrosis, in the skin and internal organs and by injuries to small arteries. There are tw ...

Polymyositis Polymyositis (PM) is a type of chronic inflammation of the muscles ( inflammatory myopathy) related to dermatomyositis and inclusion body myositis. Its name is derived . The inflammation of polymyositis is mainly found in the endomysial layer ...

Dermatomyositis Dermatomyositis (DM) is a Chronic condition, long-term inflammatory disorder, inflammatory Autoimmune disease, autoimmune disorder which affects the skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over ...

Rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and h ...

(RA) * Sjögren's syndrome *

Eosinophilic granulomatosis with polyangiitis Eosinophilic granulomatosis with polyangiitis (EGPA), formerly known as allergic granulomatosis, is an extremely rare autoimmune condition that causes inflammation of small and medium-sized blood vessels (vasculitis) in persons with a history of ...

(EGPA) *

Autoimmune thyroiditis In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an "autoimmune disease". ...

Antiphospholipid antibody syndrome Antiphospholipid syndrome, or antiphospholipid antibody syndrome (APS or APLS), is an autoimmune, hypercoagulable state caused by antiphospholipid antibodies. APS can lead to blood clots (thrombosis) in both arteries and veins, pregnancy-relate ...

The treatment of overlapping connective tissue disorders is mainly based on the use of

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...

s and

immunosuppressants Immunosuppressive drugs, also known as immunosuppressive agents, immunosuppressants and antirejection medications, are drugs that inhibit or prevent the activity of the immune system. Classification Immunosuppressive drugs can be classified ...

. 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 Vasculitis is a group of disorders that destroy blood vessels by inflammation. Both artery, arteries and veins are affected. Lymphangitis (inflammation of lymphatic vessels) is sometimes considered a type of vasculitis. Vasculitis is primarily c ...

that shares features with two or more distinct vasculitis syndromes. The most common type of polyangiitis overlap syndrome is

microscopic polyangiitis Microscopic polyangiitis is an autoimmune disease characterized by a systemic, pauci-immune, necrotizing, small-vessel vasculitis without clinical or pathological evidence of granulomatous inflammation. Signs and symptoms Clinical features may inc ...

(MPA), which shares features with EGPA,

granulomatosis with polyangiitis Granulomatosis with polyangiitis (GPA), formerly known as Wegener's granulomatosis (WG), after Nazi German physician Friedrich Wegener, is a rare, long-term, systemic disorder that involves the formation of granulomas and vasculitis, inflammatio ...

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 Autoimmune hepatitis, formerly known as lupoid hepatitis, plasma cell hepatitis, or autoimmune chronic active hepatitis, is a chronic, autoimmune disease of the liver that occurs when the body's immune system attacks liver cells, causing the liv ...

primary biliary cirrhosis Primary biliary cholangitis (PBC), previously known as primary biliary cirrhosis, is an autoimmune disease of the liver. It results from a slow, progressive destruction of the small bile ducts of the liver, causing bile and other toxins to buil ...

and

primary sclerosing cholangitis Primary sclerosing cholangitis (PSC) is a long-term progressive disease of the liver and gallbladder characterized by inflammation and scarring of the bile ducts, which normally allow bile to drain from the gallbladder. Affected individuals may ...

Cardiology

In cardiology, genetic conditions such as Brugada syndrome can share features with related disorders caused by mutations in the same

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

. An overlap syndrome can be seen whereby a mutation in the ''

SCN5A Sodium channel protein type 5 subunit alpha, also known as NaV1.5 is an integral membrane protein and tetrodotoxin-resistant voltage-gated sodium channel subunit. NaV1.5 is found primarily in cardiac muscle, where it mediates the fast influx of ...

'' gene encoding the cardiac

sodium channel Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell (biology), cell's cell membrane, membrane. They belong to the Cation channel superfamily, superfamily of cation channels. Classific ...

causes a reduction in the peak sodium current leading to the typical ECG features of Brugada syndrome, but which simultaneously increases the sustained late sodium current leading to the ECG features of Long QT syndrome type 3. Brugada syndrome can also overlap with

arrhythmogenic cardiomyopathy Arrhythmogenic cardiomyopathy (ACM) is an inherited heart disease. ACM is caused by genetic defects of parts of the cardiac muscle known as desmosomes, areas on the surface of muscle cells which link them together. The desmosomes are composed ...

due to certain mutations in the

plakophilin Plakophilin are proteins of the cytoskeleton. They are involved in regulating the adhesive activity of cadherin. The three types of plakophilin proteins found in humans are PKP1, PKP2, and PKP3; all exhibiting dual localization in the nucleus as ...

gene.

Pulmonology

In pulmonology, asthma-COPD Overlap Syndrome (ACOS) is a condition in which clinical features and symptoms of both

asthma Asthma is a common long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wh ...

and

COPD Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by chronic respiratory symptoms and airflow limitation. GOLD defines COPD as a heterogeneous lung condition characterized by chronic respiratory s ...

are present in a person and overlap significantly.

References

External links

{{Systemic connective tissue disorders Autoimmune diseases Rheumatology Syndromes