This study investigates severe chronic neutropenia (SCN), a condition where there are abnormally low levels of neutrophils, a type of white blood cell. This condition can lead to frequent infections. The purpose is to understand the natural progression of SCN and its response to treatment with a blood-stimulating factor called granulocyte colony stimulating factor (G-CSF).

Participants will undergo regular health assessments to monitor their condition and response to the treatment. The study will collect data on various health parameters, including blood counts and infection history, to better understand the effectiveness of the treatment.

• Who can participate: Individuals older than three months with a confirmed diagnosis of severe chronic neutropenia can participate. Key eligibility includes a history of recurrent infections and specific syndromes like Shwachman-Diamond syndrome or glycogen storage disease type Ib.
• Study details: Participants will need to provide health information and undergo regular assessments. The study involves monitoring the response to an investigational treatment, with some participants receiving a placebo, an inactive substance that looks like the investigational medicine but does not contain any medicine.