Pseudoxanthoma elasticum


Pseudoxanthoma elasticum

Description, Causes and Risk Factors:

Abbreviation: PXE.

Pseudoxanthoma elasticum is a systemic heritable connective tissue disorder first described in 1896 by Jean Darier. PXE is characterized by mid-to-lower dermal elastic degeneration and calcification. It is a genetic disorder primarily affecting the skin, eyes and cardiovascular system. The skin manifestations are the most prevalent characteristic of PXE and generally are the first physical signs of the developing disorder.

Almost 80% of clinical cases of pseudoxanthoma elasticum have detectable mutations in the ABCC6 gene. Mutations in almost all parts of the gene have been described, of all types (missense, nonsense, splice alteration, insertion, small deletion or large deletion). Although there have been reports of autosomal dominant inheritance, the inheritance is typically autosomal recessive (both parents need to be carriers, and there is a 25% chance that a child will inherit both abnormal copies of the gene and therefore develop the condition).

Strong genetic linkage was found with mutations in the ABCC6 gene, which codes for the MRP6 protein, but the exact mechanism by which this protein (which is a membrane transporter from the large ATP-binding cassette transporter family influences the disease course is unknown; the protein is expressed in most organs, but mainly in the liver and kidney. It is unclear in what way this would lead to abnormalities in skin, eyes and blood vessels. It is thought that particular mutations do not cause a more severe or less severe form of the disease. Given the variations in age of onset and severity it is likely that other unknown risk factors (genetic and dietary) may be involved. One study suggested that mutations causing total absence of an MRP6 protein caused a more severe disease, but this could not be confirmed in a subsequent case series.

Premature atherosclerosis is also associated with mutations in the ABCC6 gene, even in those without PXE. A syndrome almost indistinguishable from hereditary PXE has been described in patients with hemoglobinopathies (sickle-cell disease and thalassemia) through a poorly understood mechanism. In addition, there appears to be another PXE-like syndrome with a similar phenotype but as a result of problems with another gene, gamma-glutamyl carboxylase.

Presentation can be highly variable and phenotypic penetration may be incomplete. It affects females twice as often as males. It affects all races. Modes of inheritance are both autosomal dominant and autosomal recessive. 90% of cases are thought to be recessive but some may be new mutations.

Symptoms:

PXE typically causes yellow-white small raised areas in the skin folds, often appearing in the second or third decades of life. These skin abnormalities frequently appear on the neck, armpits, and other areas that bend a great deal (referred to as flexure areas). The face is not affected by PXE. The doctor can often see abnormalities in the back of the eye (retinae) called angioid streaks, which are tiny breaks in the elastin-filled tissue there. These eye abnormalities can lead to blindness.

Other areas that can be affected in PXE include the heart which can be affected by atherosclerosis and mitral valve prolapse. Small blood vessels are abnormally fragile in patients with PXE because the blood vessel walls contain elastin and are weakened. This can lead to abnormal bleeding in such areas as the bowel and, very rarely, the uterus. Impairment of circulation to the legs can lead to pains in the legs while walking (claudication).

Diagnosis:

Differential diagnosis includes actinic elastic andelastolytic dermatitis, such as cutis laxa, mid-dermalelastolysis, anetoderma, pseudoxanthoma elasticum-likepapillary dermal elastolysis, post-inflammatory elastosis and perifollicular elastolysis. However, theseentities are all characterized by loss of elastic fibers inthe dermis.

Investigations:

    Blood tests.

  • FBC for Fe-deficient anaemia from bleeding.

  • Occult blood for GI haemorrhage.

  • Urinalysis for blood.

  • Serum calcium and serum phosphate are sometimes elevated but usually normal.

Imaging:

    Plain X-rays may show calcified arteries.

  • Echocardiogram for mitral valve involvement.

  • Coronary angiography if indicated.

Other procedures:

    Ophthalmic examination is essential to detect early signs of retinopathy, angioid streaks, and retinal haemorrhages. Laser treatment may spare vision.

  • Endoscopy is indicated for any form of frank GI bleeding.

  • Ankle/brachial blood pressure using Doppler methods is useful in patients with intermittent claudication or significantly diminished peripheral pulses.

  • Biopsy can give histological confirmation of the diagnosis.

Treatment:

Currently there is no known treatment for PXE. Patients are ultimately most interested in effective treatments to ameliorate or prevent the complications of PXE, especially the visual ones, which have the greatest impact on the quality of life in affected individuals. Unless a major breakthrough in gene therapy occurs, the best hope for an effective treatment for PXE lies in basic research aimed at the defective cellular transportation mechanisms of this disorder.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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