Characterized by the deficiency or absence of the enzymes sucrase and isomaltase existing at, and usually before birth; this enzyme complex (sucrase-isomaltase) assists in the breakdown of a certain sugar (ie, sucrose) and certain products of starch digestion (dextrins); only evident soon after birth when sucrose or starches, such as found in modified milk formulas with sucrose or polycose, are ingested by an affected infant, breast-fed infants or those on lactose-only formula manifest no symptoms until such time as sucrose (found in fruit juices, solid foods, and/or some medications) is introduced into the diet.