SRP54 and Decreased total neutrophil count: In addition, we tested 5 patients with neutropenia of uncharacterized genetic origin (denoted Neutro Unkn; in 4, DNA was extracted from blood, in 1 from bone marrow), one SDS-like patient carrying biallelic SRP54 mutations32 (denoted SRP54; DNA from blood), and 15 healthy age-matched donors (denoted Ctl, DNA from blood).