Challenges of multiple mutations in individual patients with haemophilia.

Multiple mutations in the same gene within a haemophilia family are being increasingly reported and raise many issues with regard to the specificity of the mutations in causing the disease. In a proportion of families with multiple mutations, discordant phenotypic severity is often observed among the affected members. Understanding whether these mutations influence additively or non-additively the structure, stability and function of the protein will help in a better clinical evaluation of these patients. In case of haemophilia A, out of 2740 entries, ten are double mutants. Among the 2891 patient entries in the Haemophilia B mutation database, there are 34 double mutants and one triple mutant. The major challenge in patients with multiple mutations lies in genetic diagnosis and counselling especially in developing countries wherein the entire gene is not being sequenced and the screening is stopped as soon as the mutation is identified. As of now, the presence of multiple mutations stresses the importance of additional DNA testing in patients with known mutations who have unusual phenotypes or additional, unexplained clinical problems, until more cost-effective techniques for screening the entire gene are identified.