To determine whether choroid plexus ultrastructure is affected in BBS mutant mice, we used TEM to examine the brains of newborn (P0) wild- type and BBS mice and during the early stages of ventriculomegaly at P9 (the earliest stage other than P0 used in the study) (Figure 2A-D) and during its progression at 15 weeks. This evidence concerns the gene BBS2 and Bardet-Biedl syndrome.