HAX1 mutation positive children presenting with haemophagocytic lymphohistiocytosis.

The genetic basis of haemophagocytic lymphohistiocytosis (HLH) has not been elucidated in 10% of affected patients. In this study, we report four HLH episodes in three patients with HAX1 gene mutations. We screened the mutations associated with congenital neutropenia (CN) because the neutropenia persisted following HLH treatment. There were homozygous HAX1 mutations detected in all patients. This is the first case series of patients with CN caused by HAX1 mutation who presented with HLH. We hypothesize that severe neutropenia persists after an HLH episode in children without HLH mutations (especially infants) because these patients have CN caused by HAX1 mutations.