Pseudoxanthoma elasticum (PXE) is a genetic disease that causes mineralization of elastic fibers in some tissues. The most common problems arise in the skin and eyes, and later in blood vessels in the form of premature atherosclerosis. PXE is caused by autosomal recessive mutations in the ABCC6 gene on the short arm of chromosome 16 (16p13.1). Signs and symptoms
Usually, pseudoxanthoma elasticum affects the skin first, often in childhood or early adolescence. Small, yellowish papular lesions form and cutaneous laxity mainly affect the neck, axillae (armpits), groin, and flexural creases (the inside parts of the elbows and knees). Skin may become lax and redundant. Many individuals have "oblique mental creases" (horizontal grooves of the chin)PXE first affects the retina through a dimpling of the Bruch membrane (a thin membrane separating the blood vessel-rich layer from the pigmented layer of the retina), that is only visible during ophthalmologic examinations. This is called peau dorange (a French term meaning "skin of the orange"). Eventually the mineralization of the elastic fibers in the Bruch membrane create cracks called angioid streaks that radiate out from the optic nerve. Angioid streaks themselves do not cause distortion of vision, even if they cross into the foveal area. This symptom is present in almost all PXE patients and is usually noticed a few years after the onset of cutaneous lesions. These cracks may allow small blood vessels that were originally held back by Bruchs membrane to penetrate the retina.
This is the main source of circulating pyrophosphate (PPi), and individuals affected by PXE have strongly reduced plasma PPi levels, explaining their mineralization disorder. One study suggested that mutations causing total absence of an ABCC6 protein caused a more severe disease, but this could not be confirmed in a subsequent case series. Given the variations in age of onset and severity it is likely that other unknown risk factors (genetic, environmental, and lifestyle) may be involved.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. Mutations in ABCC6 can also cause generalized arterial calcification of infancy. In some cases of PXE, mutations in ABCC6 cannot be found, and other genes such as ENPP1 may be implicated

Pathophysiology
In PXE, there is mineralization (accumulation of calcium and other minerals) and fragmentation of the elastin-containing fibers in connective tissue, but primarily in the midlaminar layer of the dermis, Bruchs membrane and the midsized arteries. Recent studies have confirmed that PXE is a metabolic disease, and that its features arise because metabolites of vitamin K cannot reach peripheral tissues. Low levels of PPi cause mineralization in peripheral tissues. Diagnosis
The diagnostic criteria for PXE are the typical skin biopsy appearance and the presence of angioid streaks in the retina.