![]() X-linked means the gene is located on the X chromosome, one of two sex chromosomes. If a child is the first person in a family with the disease, the pathogenic variant may have been inherited from the mother who did not have symptoms or may have occurred by chance for the first time in the child (de novo). A man with an X-linked disease cannot pass on the disease to his sons, but all of his daughters will have a pathogenic variant in one copy of the gene. Women who have pathogenic variants in both copies of the gene would have symptoms similar to men.Ī woman who carries one X-linked pathogenic variant has a 50% (1 in 2) chance of having a son or daughter who has a pathogenic variant in one copy of the gene. ![]() Women who have a pathogenic variant in one copy of the gene usually have less severe symptoms than males who have the disease or may have no symptoms at all. Because men have only one copy of genes on the X chromosome, a pathogenic variant in one copy can cause the disease. The inheritance pattern of many X-linked diseases is not clearly dominant or recessive and so the pattern may be stated as X-linked inheritance. Genes, like chromosomes, usually come in pairs. X-linked diseases are caused by disease-causing (pathogenic) variants in genes on the X chromosome. Mutation is an older term that is still sometimes used to mean pathogenic variant.
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