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A pregnant woman who was extremely lactose intolerant asked her physician if she could still be able to breast feed her baby even though she could not drink milk or dairy products. What advice should be given?

The patient should be advised to breast feed the baby after delivery. Lactose is synthesized from UDP galactose and glucose; however galactose is not required in the diet for lactose synthesis, because galactose can be synthesized from glucose.

Lactose synthesis

Lactose is unique in the sense that it can only be synthesized in the mammary gland of the adult female for short period during lactation.Lactose synthase present in the endoplasmic reticulum of the lactating mammary gland, catalyzes the last step in the lactose biosynthesis, the transfer of galactose from UDP galactose to glucose.

Figure-showing synthesis of Lactose from UDP galactose

Lactose synthase attaches the anomeric carbon of galactose to C4 alcohol group of
glucose to form a glycosidic bond. Lactose synthase is composed of a galactosyl transferase and α lactalbumin which is a regulatory subunit. Lactose synthase is activated by Prolactin hormone. In the non lactating mammary glands, this enzyme is inactive, so lactose is not synthesized and UDP galactose is alternatively used for the formation of glycolipids or glycoproteins.

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