This chapter traverses contemporary understandings of the genetic architecture of human disease, and explores the clinical implications of the current state of knowledge. Many different classes of genetic mutations have been implicated as being involved in predisposition to certain diseases, and researchers are continually uncovering other means by which genetics plays an important role in human disease, such as with somatic genetic mosaicism. Putative “de novo” mutations can represent cases of parental mosaicism (including in the germline), which could be revealed by careful genotyping of parental tissues other than peripheral blood lymphocytes. There is an increasingly rich literature regarding rare mutations with seemingly large phenotypic effects. Privacy concerns have added to the difficulties of implementing genomics-guided medicine. With the advent of exome and whole genome sequencing (WGS), one needs to focus again on families over several generations, so as to attempt to minimize genetic differences, locus heterogeneity and environmental influences
