The search for allelic variants that cause monogenic disorders or predispose to common, complex polygenic phenotypes.

The search for the mutant genes for monogenic disorders has been a spectacular success. This was accomplished because of the mapping and sequencing of the human genome, the determination of the sequence variability, the collection of well-characterized families with mendelian disorders, the development of statistical methods for linkage analysis, and laboratory methods for mutation search. The challenge of the genetic medicine is now to decipher the nucleotide sequence variants that predispose to common complex, polygenic phenotypes. The methodology for this challenge is in development and constant evolution, it is anticipated that, in the next 10 to 20 years, susceptibility alleles for these common disorders will be identified.