An <scp>ITPR1</scp> Variant in the <scp>IP3</scp> ‐ <scp>ITPR1</scp> Binding Pocket Associated With a Clinical Phenotype of Athetoid Cerebral Palsy

A de novo, missense variant in ITPR1-inositol 1,4,5-trisphosphate receptor type 1 (ITPR1), p.(Tyr567Cys), was identified by trio whole-genome sequencing in an individual diagnosed with Spinocerebellar ataxia 29 (SCA29) who was affected by cerebral palsy and global developmental delay. The variant affects a residue involved in Inositol 1,4,5-trisphosphate (IP3)-ITPR1 binding. Genotype-Phenotype correlation analysis of the set of missense variants affecting nine residues involved in IP3-ITPR1 binding in the current case and 170 reports of individuals with ITPR1 variants showed a significantly higher frequency of phenotypic features related to neurodevelopmental delay in these variants than in other ITPR1 variants. Our proband was diagnosed with cerebral palsy, as were five other published individuals diagnosed with SCA29. Two of these individuals were siblings who were found to have the variant p.(Arg269Trp), also located in the IP3-ITPR1 binding pocket. These observations suggest that genotype-phenotype correlations exist in the ITPR1 gene and underscore the importance of data sharing and reuse to elucidate the natural history of rare neurodevelopmental diseases.