To untangle this question, and in the hope of further improving the treatment of these two genetically inherited forms of neutropenia, we characterize in depth the ability of human and mouse SGLT4 and SGLT5 to transport 1,5-AG or other sugars and show the functional impact of the rare SNPs found in SGLT5 on the transport of 1,5-AG. The gene discussed is SLC5A10; the disease is neutropenia.