Pedigree of ARPC1B-deficient patients. (A) Genetics and pedigree of families included in the study with reported mutations. Squares: male subjects; circles: female subjects; black filled symbols: patients with mutation; crossed-out symbols: deceased subjects. Each generation is designated by a roman numeral (I-II). No genomic DNA was available for testing for siblings labeled “E?”. (B) Nucleotide positions of mutations identified in index patients and representation of amino acid change caused by the mutations. (C) Crystal structure of the ARP2/3 complex from Bos taurus (access protein data bank: 1K8K), location of variants in the ARPC1B structure and modeling of c.64+1G>C splice donor and p.Val208Phe missense variants in P1 (blue) and P2 (red).