A point mutation of a nucleotide within a single gene can have a profound effect on a specific organ and or the entire human body. DNA sequences associated with human diseases may differ from the corresponding normal sequences by single nucleotide mutations or by large alterations such as deletions, insertions, duplications, or translocations of DNA segments or entire chromosomes. As a result of the heterogeneity of DNA alterations and genetic mutations, various screening approaches are required to detect these alterations. However, methods which facilitate the detection of large alterations in the genome are typically insensitive to point mutations, whereas methods which detect point mutations are not appropriate to detect large alterations within the genome. Since there is no single perfect method to screen for unknown mutations, combinations of these methods may be necessary for accurate genetic diagnosis. The applications of polymerase chain reaction (PCR) technology to genomic screening have mad e rapid and accurate genetical diagnosis possible. Furthermore, recent developments in the technology of DNA microarrays have opened the way for high throughput sequence analysis by hybridization, which shows great potential in both molecular biology and medicine in the near future.