Duffy-null Associated Neutrphil Count (DANC) Pediatric Patients

There are currently no clinical and laboratory data that well characterize this neutropenia associated with the Duffy-null phenotype, particularly for pediatric subjects. In particular there are no data on the frequency of immune neutropenia in DANC neutropenic pediatric subjects. The goal of this study is to : * define the frequency of immune neutropenia within the cohort of DANC subjects under study * evaluate the frequency of different degrees of neutropenia (mild-moderate-severe); * evaluate the possible association between different degrees of neutropenia and the presence of infections.