ITPR1 and cerebellar ataxia: The recessive alleles are predicted to generate premature termination codons that, possibly via exon skipping mechanisms, appear to act as partial rather than full loss-of-function mutations; as the carrier parents of these alleles are unaffected there is no apparent haploinsufficient effect associated with these hypomorphic variants (see below for ITPR1 haploinsufficiency in non-GS ataxia; Fig. 5).