AHI1 and Joubert syndrome: Retinal dystrophy is more strongly correlated with mutations in AHI1 than that of most other JBTS genes, but retinal involvement remains variable even with lesions in AHI1. 8 In addition to being a causative gene for JBTS, AHI1 alleles also can function as modifiers of retinal degeneration in nephronophthisis, a ciliopathy characterized by kidney dysplasia.15,16AHI1 encodes a multidomain protein also known as jouberin, which consists of an N-terminal coiled-coil domain, seven WD40 repeats, and a C-terminal SH3 domain.