 Mutations of the genes encoding these proteins have been associated with left-right axis malformations, particularly in the heart and lungs.Lefty, a divergent member of the transforming growth factor-β (TGF beta) superfamily of proteins, was originally discovered in the Hamada lab at the Osaka University using deletion screening of cDNA libraries in P19 embryonic carcinoma cells to find clones that did not differentiate when induced to differentiate using retinoic acid.From these screens, researchers found one gene that was a tentative member of the TGF-beta superfamily that was predominantly expressed on the left side the embryo and aptly named it lefty.