NPHP1 and Joubert syndrome and related disorders: Joubert syndrome-related disorders exhibit clinical heterogeneity due to their various genetic causes, including three genes (CEP290, AHI1/JBTS3, NPHP1/JBTS4) and two loci (JBTS1 and JBTS2) (Valente et al., 2005; Valente et al., 2006).