Homozygous DBF4 mutation as a cause of severe congenital neutropenia

Abstract

Background: Severe congenital neutropenia presents with recurrent infections early in life as a result of arrested granulopoiesis. Multiple genetic defects are known to block granulocyte differentiation; however, a genetic cause remains unknown in approximately 40% of cases.

Objective: We aimed to characterize a patient with severe congenital neutropenia and syndromic features without a genetic diagnosis.

Methods: Whole exome sequencing results were validated using flow cytometry, Western blotting, coimmunoprecipitation, quantitative PCR, cell cycle and proliferation analysis of lymphocytes and fibroblasts and granulocytic differentiation of primary CD34⁺ and HL-60 cells.

Results: We identified a homozygous missense mutation in DBF4 in a patient with mild extra-uterine growth retardation, facial dysmorphism and severe congenital neutropenia. DBF4 is the regulatory subunit of the CDC7 kinase, together known as DBF4-dependent kinase (DDK), the complex essential for DNA replication initiation. The DBF4 variant demonstrated impaired ability to bind CDC7, resulting in decreased DDK-mediated phosphorylation, defective S-phase entry and progression and impaired differentiation of granulocytes associated with activation of the p53-p21 pathway. The introduction of wild-type DBF4 into patient CD34⁺ cells rescued the promyelocyte differentiation arrest.

Conclusion: Hypomorphic DBF4 mutation causes autosomal-recessive severe congenital neutropenia with syndromic features.

Keywords: DBF4; DNA replication; facial dysmorphism; genetics; inborn errors of immunity; mutation; neutropenia; perturbed growth; primary immunodeficiency.