 Genetic diagnosis in HHT is difficult , as mutations occur in numerous different locations in the linked genes , without particular mutations being highly frequent ( as opposed to , for instance , the ΔF508 mutation in cystic fibrosis ) . Sequence analysis of the involved genes is therefore the most useful approach ( sensitivity 75 % ) , followed by additional testing to detect large deletions and duplications ( additional 10 % ) . Not all mutations in these genes have been linked with disease . 
