ARPC5 deficiency leads to severe early onset systemic inflammation and early mortality

The seven subunit Arp2/3 complex drives the formation of branched actin networks that are essential for many cellular processes including cell migration. In humans, the ARPC5 subunit of the Arp2/3 complex is encoded by two paralogous genes (ARPC5 and ARPC5L), resulting in proteins with 67% identity. Through whole-exome sequencing, we identified a biallelic ARPC5 frameshift variant in a female child who presented with recurrent infections, multiple congenital anomalies, diarrhea, and thrombocytopenia, and suffered early demise from sepsis. Her consanguineous parents also had a previous child who died with similar clinical features. Using CRISPR/Cas9-mediated approaches, we demonstrate that loss of ARPC5 affects actin cytoskeleton organization and function, as well as chemokine-dependent cell migration in vitro. Homozygous Arpc5-/- mice do not survive past embryonic day 9 due to severe developmental defects, including loss of the second pharyngeal arch which contributes to craniofacial and heart development. Our results indicate that ARPC5 is important for both prenatal development and postnatal immune signaling, in a non-redundant manner with ARPC5L. Moreover, our observations add the ARPC5 locus to the list of genes that should be considered when patients present with syndromic early-onset immunodeficiency, particularly if recessive inheritance is suspected. ### Competing Interest Statement The authors have declared no competing interest.