 Approximately 30 mutations that cause HFI have been identified, and these combined mutations result in a HFI frequency of 1 in every 20,000 births.Mutant alleles are a result of a number different types of mutations including base pair substitutions and small deletions.The most common mutation is A149P, which is a guanine to cytosine transversion in exon 5, resulting in the replacement of alanine at position 149 with proline.