Table 1. Diversity of HMOs based on the genetic background of the mother.

Gene	Lewis gene (+)	Lewis gene (−)
Secretor gene (+)	Lewis-positive secretors	Lewis-negative secretors
	Secrete all HMOs	Secrete 2′-FL, 3′-FL, LNFP-I, and LNFP-III
Secretor gene (−)	Lewis-positive non-secretors	Lewis-negative non-secretors
	Secrete 3′-FL, LNFP-II, and LNFP III	Secrete 3′-FL, LNFP-III, and LNFP-V

HMO: human milk oligosaccharide, 2′-FL: 2′-fucosyllactose, LNFP: lacto-N-fucopentaose.