[Complex diseases genetics].

Common diseases are not inherited in a mendelian way, but have got anyway a genetic component, as shown by their increased frequency in siblings. Differences in the genome of individuals are not bigger than 0.1%, but are the reason why the susceptibility to diseases, their prognosis and the response to treatments differ. There are approximately ten million variations in the human genome, most of them single nucleotide polymorphisms (SNP) but also insertions, duplications, deletions, inversions and translocations. Two big international projects finished at the beginning of this century (The Human Genome Project and the HapMap Project) have paved the way to the study of these variations. The rapid technological advances allow today the study of one million SNPs at one time and it is forecasted that is some years the whole human genome will be sequenced in a few hours. All this is making possible new discoveries of the genetic variations that confer susceptibility to diseases, the location of new therapeutic targets and the beginning of a new medicine: personalized medicine.