For people with milk allergies, remedies beyond abstaining from dairy products are limited. But now scientists have come up with a solution sure to cheer all those whose hearts scream for ice cream but whose immune systems scream in protest: a genetically engineered cow that makes potentially hypoallergenic milk.

Many milk allergies are thought to be the result of a person's immune system overreacting to beta-lactoglobulin, or BLG, a whey protein found in the milk of many mammals, including cows, but which is notably not present in human milk. A milk allergy is not the same thing as lactose intolerance, which derives from an inability to digest the sugar lactose and is the norm for most human adults.

But milk allergies can strike even in very young children, potentially depriving them of a calcium source.

BLG isn’t thought to be an essential component of milk -- after all, human mothers lactate just fine without making it -- so a group of New Zealand researchers set about trying to genetically manipulate a cow so it would make milk with reduced or completely eliminated BLG. In order to suppress genes that make BLG, the researchers used a technique called RNA interference, which uses small pieces of RNA to tamp down the expression of target genes. They described their success in a paper published in the Proceedings of the National Academy of Sciences on Monday.

University of Waikato researcher Anower Jabed and his colleagues at the New Zealand-based company AgResearch first tested their concept in mice with mammary glands designed to mimic those of sheep. When the mouse produced milk with a 96 percent reduction in BLG, the scientists set about making a transgenic calf with the same interfering RNAs.

When the researchers induced lactation in the calf with hormones, the resulting milk had no detectable traces of BLG. Meanwhile, the engineered calf’s milk had increased levels of all of the other major milk proteins.

It remains to be seen whether removing BLG means the milk will actually be hypoallergenic, but now researchers have a way to directly test this hypothesis.

“Furthermore, the BLG knockdown cattle line will provide the opportunity to fully investigate the impact of the associated milk composition changes on nutritional and processing properties and will provide new insights into the still obscure biological function of BLG,” the authors wrote.

Then perhaps, the researchers can turn to even more important work: breeding special lines of cows that make chocolate, strawberry or coffee milk.

SOURCE: Jabed et al. “Targeted micro RNA expression in dairy cattle directs production of beta-lactoglobulin-free, high casein milk.” PNAS published online 1 October 2012.