What causes severe combined immunodeficiency?

Your immune system is made up of many different white blood cells. They destroy anything unfamiliar in your body, including bacteria and viruses, which can all cause illness. In boys with X-linked SCID, some of these 'defender cells' do not develop and grow properly. This is because they have no working version of a gene that normally makes a protein found on the surface of these cells.

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Red and white blood cells.

How is severe combined immunodeficiency inherited?

X-linked SCID is caused by an altered gene found on the X-chromosome, so the disorder usually affects only boys. In some cases, the disease appears 'out of the blue', following a genetic change in the unfertilised egg. In others, the affected boy inherits SCID from his carrier mother. A carrier woman has a one-in-four chance of having an affected son, and a one-in-four chance of having a carrier daughter.

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Inheritance of severe combined immunodeficiency.

 

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