To begin to understand the genes and pathways underlying hydrocephalus susceptibility, we performed a DNA microarray analysis to identify strain-specific differences in gene expression in whole brains from wild type mice and nm1054 mice lacking ciliary protein CFAP221 (previously known as PCDP1), as the phenotypic differences have been well characterized and are particularly dramatic in this line20,23. The gene discussed is CFAP221; the disease is Hydrocephalus.