Mutations in BBS genes cause changes in the proteins that are needed for the correct functioning of a particular part of the cell called a primary cilium. For this reason, BBS has been categorized medically as a ciliopathy.
Ciliopathies are a range of human disease syndromes all caused by defects in primary cilia function. Examples of other ciliopathies include Alström Syndrome, Primary Ciliary Dyskinesia, Polycystic Kidney Disease, some forms of Retinitis Pigmentosa, Nephronophthisis, Joubert Syndrome and Meckel Syndrome, which have overlapping symptoms, all caused by defects in cilia proteins.
Cilia are long thin, hair-like projections that stick out of the surface of a cell. There are two types of cilium, motile and non-motile or primary cilia (also called sensory cilia). Many cell types in the body rely on having a fully functional primary cilium. Important examples include the retinal photoreceptor in the eye, and cells in the kidney. The scientific community is trying to understand exactly what roles the BBS proteins play in cilia formation and function.