In the context of ataxia as a leading symptom of GAN-related neurodegeneration, it is important to note that HYOU1 (GRP170/ ORP150), a co-chaperone of BiP (the major chaperone of the endoplasmic reticulum), is decreased in white blood cells derived from GAN patients and that bi-allelic variants in three other binding partners of BiP (SIL1, INPP5K, and DNAJC3) were already linked to phenotypes associated with ataxia [23–25], thus indicating a profound role of BiP and its binding partners in cerebellar maintenance. Here, AQP1 is linked to cerebellar ataxia.