Pseudoxanthoma elasticum (PXE)
Pseudoxanthoma elasticum or PXE (pronounced ‘pixie’) is a disease affecting many parts of the body. It causes calcium and other minerals to build up in various body tissues, especially those which are usually elastic, such as the skin on the neck, armpits and knees. Affected skin develops a yellow, waxy, ‘cobblestone’ appearance and forms loose folds.
PXE can also affect blood vessels and the digestive system. In the eyes, it causes cracks to form in a tissue called Bruch’s membrane. Leaky blood vessels grow through these cracks, which can lead to sight loss.
How is it inherited?
Most cases are caused by a mutation in a gene called ABCC6. As PXE is an autosomal recessive condition, only someone who inherits a faulty copy of the gene from both parents will develop it.
Children who have one parent with PXE will be carriers, but will not develop it unless their other parent is also a carrier.
If both parents are carriers, there is around a 25 per cent chance that a child will develop PXE, and a 50 per cent chance that they will carry the faulty gene without any symptoms.
People with one carrier parent have a 25 per cent chance of being a carrier, but will not develop PXE.
The ‘cobblestone’ skin lesions, which can appear in childhood or much later, are often the first sign of PXE, before any noticeable sight loss.
Examining the retina will then show up an ‘orange peel’ effect or wiggly cracks called angioid streaks. Neither of these will cause sight loss in themselves.
Later, usually in middle age, blood vessels can grow through the cracks (similarly to wet age-related macular degeneration ) and leak. This scars the macula, leading to distortion and central vision loss. In most people, the peripheral vision is not affected.
Symptoms vary between people, even within the same family, but can include bleeding in the stomach, skin lesions, sight loss and cramp when walking. Women are around twice as likely to be diagnosed with PXE than men, but it’s not yet clear why.
At the moment, there is no way to prevent PXE affecting various body tissues – instead, each symptom is treated as and when it appears.
Injections of anti-VEGF treatments (like those used in wet AMD) are effective at slowing the growth of damaging blood vessels in the eye. Laser treatment is not usually used as it can cause further sight loss.
Current research is investigating why this particular mutation causes mineral build-up and how the progression can be slowed.
PXE patients also need to be assessed by a heart specialist (cardiologist) for potential heart problems.