| Unlike haemophilia, von Willebrand disease is not gender-related. So the effect is the same regardless of whether the defective von Willebrand factor (vWF) is passed down from the mother or father. It also makes no difference whether the child is a boy or girl; the disease shows up in the same way.
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If one parent has a defective gene:
Each parent contributes one of his/her genes for vWF to his/her child. As shown, there are four possible genetic combinations than can result from this union.
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If both parents have a defective gene:
Again, there are four possible genetic combinations.
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Odds:
2 out of 4 children (50%) will be genetically normal.
2 out of 4 children (50%) will have the defective vWF gene. |
Odds:
1 out of 4 children (25%) will be genetically normal.
2 out of 4 children (50%) will have one defective vWF gene
1 out of 4 children (25%) will have two defective vWF genes, which will result in severe von Willebrand disease.
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Von Willebrand types I and II have a "dominant" inheritance pattern.
That means that in a child with one normal gene and one gene for either of these von Willebrand types, the defective gene in "stronger. So the child will actually have the disease. |
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Von Willebrand type III has a recessive inheritance pattern.
In a child with one normal gene and one gene for von Willebrand type III, the defective gene is "weaker", so the child will be a carrier for the disease, but will not have it.
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In order to have von Willebrand type III, the child must have two genes for the disease. |
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