Genotype-Phenotype Heterogeneity in Haemophilia

Abstract

Haemophilia was previously regarded as a classical example of Mendelian inheritance, with mutation in only a single gene (F8 or F9) causing the disease phenotype. The disease manifests complete penetrance. Studies, however, revealed the striking genetic and phenotypic heterogeneities of the disease. With further sophistication of clinical and molecular techniques, the disease was also found to have allele heterogeneity, phenotypic plasticity and variation in expressivity. The variations are more pronounced in F9 variants with five distinct phenotypes. All these phenomena advocate a rather complex genotype-phenotype relationship for the disease. A keen insight into the matter may unveil new avenues of therapeutics.