ELDER TIP In older adults, platelet characteristics change. Granular constituents decrease and platelet-release factors increase. These changes may reflect diminished bone marrow and increased fibrinogen levels.
An idiopathic form of thrombocytopenia commonly occurs in children. A transient form may follow viral infection (such as Epstein-Barr virus or infectious mononucleosis).
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Source: Professional Guide to Diseases (Eighth Edition), 2005
Wiskott-Aldrich syndrome:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
Because Wiskott-Aldrich syndrome results from an X-linked recessive trait, it affects only males. Children with this genetic defect are born with a normal thymus gland, plasma cells, and lymphoid tissues. However, an inherited defect in both B-cell and T-cell function compromises the child’s immune system response and increases his vulnerability to infection. These children also have a metabolic defect in platelet synthesis that causes them to produce only small, short-lived platelets, resulting in thrombocytopenia.
Wiskott-Aldrich syndrome occurs in 4 neonates per 1 million live births.
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Source: Professional Guide to Diseases (Eighth Edition), 2005
Acquired immunodeficiency syndrome:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
AIDS results from infection with HIV, which has two forms: HIV-1 and HIV-2. Both forms of HIV have the same modes of transmission and similar opportunistic infections associated with AIDS, but studies indicate that HIV-2 develops more slowly and presents with milder symptoms than HIV-1.
Transmission occurs through contact with infected blood or body fluids and is associated with identifiable high-risk behaviors. It’s disproportionately represented in:
❑ homosexual and bisexual men
❑ persons who use illicit I.V. drugs
❑ neonates of infected females
❑ recipients of contaminated blood or blood products (incidence dramatically decreased since mid-1985)
❑ heterosexual partners of persons in the former groups.
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Source: Professional Guide to Diseases (Eighth Edition), 2005
Common variable immunodeficiency:
Causes
(Professional Guide to Diseases (Eighth Edition))
The cause of common variable immunodeficiency is unknown. Most patients have a normal circulating B-cell count but defective synthesis or release of immunoglobulins. Many also exhibit progressive deterioration of T-cell (cell-mediated) immunity revealed by delayed hypersensitivity skin testing.
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Source: Professional Guide to Diseases (Eighth Edition), 2005
Severe combined immunodeficiency disease:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
SCID is usually transmitted as an autosomal recessive trait, although it may be X-linked. In most cases, the genetic defect seems associated with failure of the stem cell to differentiate into T and B lymphocytes. Many molecular defects such as mutation of the kinase ZAP-70 can cause SCID. X-linked SCID is due to a mutation of a subunit of the interleukin (IL)-2, IL-4, and IL-7 receptors. Less commonly, it results from an enzyme deficiency.
SCID affects more males than females. Its estimated incidence is 1 in every 100,000 to 500,000 births. Most untreated patients die from infection within 1 year of birth.
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Source: Professional Guide to Diseases (Eighth Edition), 2005
Thrombocytopenia:
Causes
(Handbook of Diseases)
Thrombocytopenia may be congenital or acquired; the acquired form is more common. In either case, it usually results from the following:
❑ decreased or defective production of platelets in the marrow (such as occurs in leukemia, aplastic anemia, or toxicity with certain drugs)
❑ increased destruction outside the marrow caused by an underlying disorder (such as cirrhosis of the liver, disseminated intravascular coagulation, or severe infection)
❑ less commonly, sequestration (hypersplenism, hypothermia) or platelet loss.
Acquired thrombocytopenia may result from certain drugs, such as nonsteroidal anti-inflammatory agents, sulfonamides, histamine blockers, alkylating agents, heparin, alcohol, or antibiotic chemotherapeutic agents.
An idiopathic form of thrombocytopenia commonly occurs in children. A transient form may follow viral infections (Epstein-Barr or infectious mononucleosis).
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Source: Handbook of Diseases, 2003
Common variable immunodeficiency:
Causes
(Handbook of Diseases)
Exactly what causes common variable immunodeficiency is unknown. Most patients have a normal circulating B-cell count but defective synthesis or release of immunoglobulins. Many also exhibit progressive deterioration of T-cell (cell-mediated) immunity, which is revealed by delayed hypersensitivity skin testing.
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Source: Handbook of Diseases, 2003
Human immunodeficiency virus infection:
Causes
(Handbook of Diseases)
The virus has two major strains: HIV-1, which is closely related to the primate retrovirus called simian immunodeficiency virus, and HIV-2, which is associated with immunodeficiency but less pathogenic that HIV-1, results from infection with HIV, which strikes cells bearing the CD4+ antigen; the latter (normally a receptor for major histocompatibility complex molecules) serves as a receptor for the retrovirus and lets it enter the cell. HIV prefers to infect the CD4+ lymphocyte or macrophage but may also infect other CD4+ antigen-bearing cells of the GI tract, uterine cervical cells, and neuroglial cells. The virus gains access by binding to the CD4+ molecule on the cell surface along with a co-receptor (thought to be the receptor CCR5). After invading a cell, HIV either replicates, which leads to cell death, or becomes latent. HIV infection leads to profound pathology, either directly, through destruction of CD4+ T cells, other immune cells, and neuroglial cells, or indirectly, through the secondary effects of CD4+ T-cell dysfunction and resultant immunosuppression.
The infection process takes three forms:
❑ immunodeficiency (opportunistic infections and unusual cancers)
❑ autoimmunity (lymphoid interstitial pneumonia, arthritis, hypergammaglobulinemia, and production of autoimmune antibodies)
❑ neurologic dysfunction (AIDS dementia complex, HIV encephalopathy, and peripheral neuropathies).
Transmission
HIV is transmitted by direct inoculation during intimate sexual contact, especially associated with the mucosal trauma of receptive rectal intercourse; transfusion of contaminated blood or blood products (a risk diminished by routine testing of all blood products); sharing of contaminated needles; or transplacental or postpartum transmission from an infected mother to the fetus (by cervical or blood contact at delivery and in breast milk).
HIV isn’t transmitted by casual household or social contact. The average time between exposure to the virus and diagnosis is 8 to 10 years, but shorter and longer incubation times have also been recorded. Most people develop antibodies within 6 to 8 weeks of contracting the virus.
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Source: Handbook of Diseases, 2003
Severe combined immunodeficiency disease:
Causes
(Handbook of Diseases)
SCID is usually transmitted as an autosomal recessive trait, although it may be X-linked. In most cases, the genetic defect seems associated with failure of the stem cell to differentiate into T and B lymphocytes.
Many molecular defects, such as mutation of the kinase ZAP-70, can cause SCID. X-linked SCID results from a mutation of a subunit of the interleukin-2 (IL-2), IL-4, and IL-7 receptors. Less commonly, it results from an enzyme deficiency.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
Wiskott Aldrich Syndrome:
Wiskott Aldrich Syndrome - etiology
(The 5-Minute Pediatric Consult)
- Mutations in the gene for the Wiskott–Aldrich syndrome protein (WAS).
- WAS protein (WASP) is involved in the reorganization of the actin cytoskeleton in hematopoietic cells.
- Following activation of WASP, reorganization of actin cytoskeleton results in polarization of cells (e.g., polarized actin mesh in platelets for clotting, in macrophages for phagocytosis, and polarization of T or B cells to form immunologic synapses).
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Source: The 5-Minute Pediatric Consult, 2008
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