Advanced technology has recently allowed us to study rare Mendelian disorders in an unprecedented manner. The same technology should allow us also to study more common malformations. Many of these are not caused by a variant in a single Mendelian gene but by interplay between series of genetic variants and exogenous influences. Likely the site from which the DNA is derived is of great importance in studying malformations as mosaicism may be much more common than earlier anticipated. Factors other than simple variants in our genomic DNA should be considered in the studies as well. Not only is recognition of someone's liability to disease important, but also determining exogenous factors involved in malformations should receive more attention as it may allow us decrease the burden of malformations in humans.