There have been great strides in using positional cloning to successfully identify the underlying basis of many Mendelian disorders of children. The severity of even these disorders, however, is greatly affected by genetic modifiers and gene- environment interactions. The molecular pathogenesis of many more complex disorders remains unexplained due to the often complex genetic, epigenetic and environmental interactions involved in their etiology. However, there is reason for optimism. New genomic technologies – single nucleotide polymorphism (SNP) and copy number variant (CNV) arrays, comparative genomic hybridization (CGH) arrays, and next generation sequencing – increasingly allow genome-wide analyses at a reasonable.
