Abstract
In 1964, since Vogel made the first preliminary estimate of the number of genes in the human genome [1] (6.7 million), it has now become clear that the number of genes in the human genome is likely to be about 22,500 [2]. These genes are constructed from 43 billion base pairs, although most base pairs are recognized as non-coding DNA. However, it now becomes clear that this non-coding DNA also has essential regulatory tasks [3]. Each human and his or her genome differ from another at millions of base pairs. This natural variation creates human diversity, and the vast majority of the varying base pairs are known as single nucleotide polymorphisms (SNPs). SNPs occur frequently and are not considered to be mutations or directly disease causing. Their original definition included an occurrence of 41% in a given population, although some also consider variations with lower prevalence, while others focused on the impact of variations that are more common, e.g., with an occurrence of 410% [4]. The development of genome-wide association studies (GWAS) for the analysis between phenotypes and genotypes based on associations between a phenotype and (multiple) SNPs has changed today's research on risk assessment and heritability issues. For most inheritable diseases, it is now clear that there is much more to a disease phenotype than a single mutation in an essential gene. Instead of this monogenic disease model, the complex interplays between many more genetic variations with or without a mutated gene (i.e., the polygenic disease model) and epigenetic and non-genetic phenomena (think of preferred expression of either maternal or paternal genes, ageing, smoking, diet, sun exposure, etc.) declare the phenotypic expression of a patient. The phenotype for patients carrying the same mutation can thus range from a normal phenotype
Published Version
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