In this context, it is interesting to note that mutations in genes encoding various TZ proteins, such as TMEM216/MKS2/JBTS2 and TMEM67/MKS3/JBTS6, are known to cause JBTS (Braun and Hildebrandt, 2017; Parisi and Glass, 2017); therefore, impaired integrity of the TZ might result in its impaired role as a diffusion barrier (Okazaki et al., 2020). Here, TMEM67 is linked to Joubert syndrome.