Mutations in the SRP54 gene cause severe congenital neutropenia as well as Shwachman-Diamond–like syndrome

Abstract

Congenital neutropenias (CNs) are rare heterogeneous genetic disorders, with about 25% of patients without known genetic defects. Using whole-exome sequencing, we identified a heterozygous mutation in the <i>SRP54</i> gene, encoding the signal recognition particle (SRP) 54 GTPase protein, in 3 sporadic cases and 1 autosomal dominant family. We subsequently sequenced the <i>SRP54</i> gene in 66 probands from the French CN registry. In total, we identified 23 mutated cases (16 sporadic, 7 familial) with 7 distinct germ line <i>SRP54</i> mutations including a recurrent in-frame deletion (Thr117del) in 14 cases. In nearly all patients, neutropenia was chronic and profound with promyelocytic maturation arrest, occurring within the first months of life, and required long-term granulocyte colony-stimulating factor therapy with a poor response. Neutropenia was sometimes associated with a severe neurodevelopmental delay (n = 5) and/or an exocrine pancreatic insufficiency requiring enzyme supplementation (n = 3). The SRP54 protein is a key component of the ribonucleoprotein complex that mediates the co-translational targeting of secretory and membrane proteins to the endoplasmic reticulum (ER). We showed that SRP54 was specifically upregulated during the in vitro granulocytic differentiation, and that <i>SRP54</i> mutations or knockdown led to a drastically reduced proliferation of granulocytic cells associated with an enhanced P53-dependent apoptosis. Bone marrow examination of <i>SRP54</i>-mutated patients revealed a major dysgranulopoiesis and features of cellular ER stress and autophagy that were confirmed using <i>SRP54</i>-mutated primary cells and <i>SRP54</i> knockdown cells. In conclusion, we characterized a pathological pathway, which represents the second most common cause of CN with maturation arrest in the French CN registry.