Inheritance of PXE

extracts from an article by Kenneth H Neldner MD

It has been known for well over 50 years that PXE is a hereditary disorder that is passed from one generation to the next through the genes, although the specific details are complex and not totally understood. It is accepted, however, that the PXE gene passes only recessively; it is never a dominant gene.

In Rececessive (AR) inheritance, it takes two defective recessive genes - one from each parent - to produce the disorder. The parents who are carriers of the PXE gene, may be totally unaware of the fact that they are carrying a PXE gene. The children of two parents who each carry the PXE gene will have a 25% chance of getting a PXE gene from each parent and will then develop PXE; 50% of the children will only get one PXE gene and will be carriers but will not develop PXE; 25% will get two completely normal genes. Once again these are statistical odds, based on large numbers, so any family with four children, for example, would not necessarily have a genetic split as presented, unless there were at least a hundred children! In AR inheritance, it is also quite common to see two or more affected siblings in a family, but again, their parents and the children of the affected siblings should not have PXE. An illustration of the three examples of recessive inheritance is shown below.

There are three possible situations shown, using diamond-shaped outlines to indicate either male or female. The X-shaped structures represent chromosomes. The blackened chromosomes carry the PXE gene and a darkened diamond means that the person has PXE. The upper left example "A" shows how a recessive chromosome (carrying a PXE gene) can be transmitted from generation to generation without anyone developing PXE. lf only one parent has the PXE gene, half of their children will be PXE carriers but none will have PXE. The upper right example "B" brings two carriers together and on average, PXE will develop in 25% of the children; 50% will be carriers and 25% will have normal genes. The lower example "C" illustrates the fact that if someone with PXE marries someone with two normal genes, their children will be carriers, but none will develop PXE.