We have demonstrated that congenic mouse models of PCD lacking ciliary proteins CFAP221, CFAP54 and SPEF2 all have a severe hydrocephalus on the C57BL6/J (B6) background but not on 129S6/SvEvTac (129) or a mixed (B6x129)F1 background20–22, indicating strain specificity in susceptibility to severe PCD-associated hydrocephalus. This evidence concerns the gene SPEF2 and Hydrocephalus.