Hundreds of defects in the FVIII gene have been shown to cause hemophilia A. These include deletions of varying sizes in the gene, stop codons, frameshift mutations, and point mutations. Inversion of the gene is the most common mutation. The same types of defects are found in the FIX gene. This makes population screening for hemophilia impractical: There are too many possible mutations to screen for. However, affected members of a given family will all have the same defect.
It is useful to determine (by gene analysis) which defect is present in the FVIII or FIX gene of a particular family with hemophilia, so that one can look for this defect in possible carrier females. Identification of carrier females permits genetic counseling and decision making, on the part of parents, regarding childbearing.
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