Later, a study of several patients with severe congenital neutropenia (SCN) identified haematopoietic cell-specific Lyn substrate 1-associated gene X1 (HAX1), located in 1q22, as the gene responsible for a type of SCN (Melin et al., 2007), while that same year gene mutations causing unexpected stop codon, such as W44X, R86X, and Q190X of HAX1, were reported to be responsible for Kostmann syndrome (Klein et al., 2007). Here, HAX1 is linked to severe congenital neutropenia.