Genetics of human situs abnormalities

Human left-right malformations are usually sporadic, but many familial cases have been described. Recognition of these families as well as sporadic cases with underlying cytogenetic abnormalities suggest genetic predisposition for many instances of situs malformations. Studies in nonhuman vertebrates have led to the discovery of several genes conserved in normal left-right development, and mutations in some of these have been identified in humans. In addition, positional cloning efforts have yielded some success in enlarging our understanding of the molecular genetics of human left-right anomalies.