Cornelius F. Boerkoel

To date, PACS1 ‐neurodevelopmental disorder ( PACS1 ‐NDD) has been associated with recurrent variation of Arg203 and is considered diagnostic of PACS1 ‐NDD, an autosomal dominant syndromic intellectual disability disorder. Although incompletely defined, the proposed disease mechanism for this variant is altered PACS1 affinity for its client proteins. Given this proposed mechanism, we hypothesized that PACS1 variants that interfere with binding of adaptor proteins might also give rise to syndromic intellectual disability. Herein, we report a proposita and her mother with phenotypic features overlapping PACS1 ‐NDD and a novel PACS1 variant (NM_018026.3:c.[755C > T];[=], p.(Ser252Phe)) that impedes binding of the adaptor protein GGA3 (Golgi‐associated, gamma‐adaptin ear‐containing, ARF‐binding protein 3). We hypothesize that attenuating PACS1 binding of GGA3 also gives rise to a disorder with features overlapping those of PACS1‐NDD. This observation better delineates the mechanism by which PACS1 variation predisposes to syndromic intellectual disability.