The Land Between Mendelian and Multifactorial Inheritance

Abstract
Bardet-Biedl syndrome (BBS) is a heterogeneous multigenic disease that turns out to have an unusual form of inheritance ( Katsanis et al.). As Burghes et al. explain in their Perspective, the disease phenotype only appears if one copy of a modifier gene at one of five loci is mutated in addition to the two copies of the BBS gene at the sixth locus.