Pedigrees of families and genetic findings in EXOC2-deficient families. (A) Pedigrees of Families 1 and 2 and confirmatory Sanger sequencing. Family 1 has a homozygous c.1309C>T; p.Arg437* EXOC2 variant in the affected patients, a heterozygous variant in each parent, and homozygous wild-type or heterozygous configuration in unaffected tested siblings. (B) The affected individual in Family 2 has compound heterozygous variants [c.389G>A; p.Arg130His and c.1739T>C; p.Leu580Ser] with one allele inherited from each parent. (C) qRT-PCR in control (C1 and C2) and patient (P2 and P3) fibroblasts showed a significant decrease in EXOC2 transcript abundance in Patient 2 fibroblasts compared with controls. Cycloheximide treatment (+CHX) prevented nonsense-mediated decay and partially restored transcript abundance in Patient 2 fibroblasts. Transcript abundance in Patient 3 was comparable to that of controls. (D) Multiple sequence alignment of EXOC2 and related proteins was performed using the Multiz Alignment of 100 vertebrates. The pathogenic EXOC2 variants are in highly conserved regions (highlighted in yellow). Asterisk indicates ES. Data in C are mean ± SD; n > 3 per measurement from at least three biological collections of each cell line, duplicate qPCR reactions, and representative of two independent EXOC2 primer pairs and normalized against three housekeeper genes. Statistical significance was determined using two-way ANOVA with Sidak correction for multiple comparisons versus sample C1. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.