Wiskott-Aldrich syndrome
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Wiskott-Aldrich syndrome (WAS) is a rare X-linked recessive disease characterized by eczema, thrombocytopenia (low platelet counts), immune deficiency, and bloody diarrhea (due to the low platelet counts). It is also sometimes called the eczema-thrombocytopenia-immunodeficiency syndrome in keeping with Aldrich's original description in 1954.
Signs and symptoms
WAS generally becomes symptomatic in children. Due to its mode of inheritance, the overwhelming majority are male. It is characterised by bruising caused by thrombocytopenia (low platelet counts), small platelet size on blood film, eczema, recurrent infections, and a propensity for autoimmune disorders and malignancies (mainly lymphoma and leukemia).In Wiskott-Aldrich syndrome, the platelets are small and do not function properly. They are removed by the spleen, which leads to low platelet counts. Also, patients develop a type of itchy rash called eczema. Autoimmune disorders are also found in patients with WAS.
Diagnosis
The diagnosis is made on the basis of clinical parameters, the blood film and low immunoglobulin levels. Skin immunologic testing (allergy testing) may reveal hyposensitivity. It must be remembered that not all patients will have a family history, since they may be the first to harbor the gene mutation. Often, leukemia may initially be suspected on the basis of the low platelets and the infections, and bone marrow biopsy may be performed. Decreased levels of Wiskott-Aldrich syndrome protein and/or confirmation of a causative mutation provides the most definitive diagnosis.Classification
Jin et al (2004) employ a numerical grading of severity:- 0.5: intermittent thrombopenia
- 1.0: thrombopenia and small platelets
- 2.0: thrombopenia and normally responsive eczema or occasional upper respiratory tract infections.
- 2.5: thrombopenia and therapy-responsive but severe eczema or airway infections requiring antibiotics
- 3.0: both eczema and airway infections requiring antibiotics
- 4.0: eczema contiuously requiring therapy and/or severe/lifethtreatening infections
- 5.0: autoimmune disease or malignancy in an XLT/WAS patient.
Pathophysiology
Wiskott-Aldrich syndrome was linked in 1994 to mutations in a gene on the short arm of the X chromosome, which was termed Wiskott-Aldrich syndrome protein (WASP). It was later discovered that the disease X-linked thrombocytopenia (XLT) was also due to WASP mutations, but different ones from those that cause full-blown Wiskott-Aldrich syndrome. Furthermore, the rare disorder X-linked neutropenia has been linked to particular mutations of the WASP gene.The WASP gene codes for the protein by the same name, which is 502 amino acids long and is mainly expressed in hematopoietic cells (the cells in the bone marrow that develop into blood cells). Its exact function is being investigated, but signal transduction and cytoskeleton maintenance have been suggested.
The immune deficiency is caused by decreased antibody production, although T cells are also affected (making it a combined immunodeficiency). This leads to increased susceptibility to infections, particularly of the ears and sinuses.
The type of mutation to the WASP gene correlates significantly with the degree of severity: those that led to the production of a truncated protein caused significantly more symptoms than those with a missense mutation but a normal-length WASP (Jin et al 2004). Although autoimmune disease and malignancy occur in both types of mutation, those patients with truncated WASP carry a higher risk.
Epidemiology
The combined incidence of WAS and XLT is about 4-10 in 1 million live births. There is no geographical factor.Treatment
Treatment of Wiskott-Aldrich syndrome is based on correcting symptoms. Aspirin and other non-steroidal anti-inflammatory drugs should be avoided, since these may interfere with platelet function. A protective helmet can protect children from bleeding into the brain which could result from head injuries. For severely low platelet counts, patients may require platelet transfusions or a splenectomy. For patients with frequent infections, intravenous immunoglobulins (IVIG) can be given to boost the immune system. Anemia from bleeding may require iron supplementation or blood transfusion.As Wiskott-Aldrich syndrome is primarily a disorder of the blood-forming tissues, a bone marrow transplant or cord blood stem cell transplant offers the only hope of cure. This treatment is, however, inherently fraught with risks, and is therefore reserved in those patients with severe infections.
History
The syndrome is named after Dr Robert Anderson Aldrich, an American pediatrician who described the disease in a family of Dutch-Americans in 1954, and Dr Alfred Wiskott, a German pediatrician who first noticed the syndrome in 1937.References
- Wiskott A. Familiärer, angeborener Morbus Werlhofii? ("Familial congenital Werlhof's disease?") Montsschr Kinderheilkd 1937;68:212-6.
- Aldrich RA, Steinberg AG, Campbell DC. Pedigree demonstrating a sex-linked recessive condition characterized by draining ears, eczematoid dermatitis and bloody diarrhea. Pediatrics 1954;13:133-9.
- Jin Y, Mazza C, Christie JR, Gillani S, Fiorini M, Mella P, Gandellini F, Stewart DM, Zhu Q, Nelson DL, Notarangelo LD, Ochs HD. Mutations of the Wiskott-Aldrich Syndrome Protein (WASP): hotspots, effect on transcription, and translation and phenotype/genotype correlation. Blood 2004;104:4010-9. PMID 15284122.
External links
- OMIM [301000]
- [Immune Deficiency Foundation] - Chapter VII, "The Wiskott-Aldrich Syndrome"
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