Although the Human Genome Project discovered the sequence of the human genetic information 15 years ago, genetic background of the diseases - primarily that of complex disorders - is still not known. The sum of the not yet discovered inherited risk factors is termed the missing heritability; the identification of these genetic components is, however, essential, as it is the base of the understanding of the molecular pathomechanism of diseases. It is not only of theoretical importance: this knowledge can be used in the clinical practice, as it offers the possibility of improvement of diagnostics, prevention as well as targeted and individualized therapy. Application of novel and more efficient molecular biological tools contribute to the discovery of unknown genetic factors, the complete goal can only be achieved, however, by re-conceptualization of several clinical and genetic points. Our knowledge was established by genome-wide studies, however, further knowledge must be acquired according to the following points: (1) genotype and association analysis of repeat variations (VNTRs and CNVs) besides SNPs, (2) investigation of gene-gene and gene-environment interactions, (3) epigenetic studies, (4) assessing the biological function of polymorphisms, (5) application of biologically relevant diagnostic categories and endophenotypes. Although it is only 1.2% of the whole genome that codes for proteins, however, as much as 90% is transcribed to RNA, consequently it can be hypothesized that gene expression analyses might offer promising starting points for further studies, as they can shed light on the molecular processes that contribute to the development of diseases.
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