NIPBL and Cornelia de Lange syndrome: If phenotypes in nipbl-morphant zebrafish are indeed explained by the cooperative effects of quantitative changes in gene expression, it not only provides a framework for understanding specific classes of birth defects syndromes, such as CdLS and the cohesinopathies; it also suggests a mechanism by which non-syndromic birth defects (which are far more common) might naturally arise out of combinations of quantitative genetic variants in the human population.