Detection of Microsatellite Instability in Cancers by Means of Nongel-Sieving Capillary Electrophore

Microsatellite instability has been shown to be relevant to various human diseases, including fragile X syndrome ( 1 ) and Huntington’s disease ( 2 ). In several human cancers, it has been reported that an increase or decrease in the number of repeat units between lymphocyte and tumor DNA derived from the same patient was found ( 3 , 4 ). Therefore, the analysis of microsatellite DNA has become necessary for the diagnosis of various diseases, especially hereditary and sporadic cancers ( 3 , 4 ). In hereditary nonpolyposis colorectal cancer (HNPCC), abnormalities of microsatellite DNA, (CA)n repeats, were reported to be an effective marker of microsatellite instability ( 5 , 6 ). The (CA)n repeats, which are related to HNPCC, are located on D2S123 marker DNA of the second chromosome. It is supposed that the alteration of (CA)n repeats might be associated with a defect in an early step of mismatch repair, and is controlled by mutator gene products such as hMSH2 ( 11 ). For the analysis of microsatellite instability, the PCR technique has been applied ( 5 , 8 ). DNA fragments containing (CA)n repeats can be amplified using specific primers ( 8 ; Fig. 1 ). The increase or decrease in the (CA) repeat number has been determined by evaluation of amplified DNA fragments by gel electrophoresis ( 8 ).   Fig. 1.  Detection of (CA)n repeat “D2S123” alterations. ( A ) Primers used for amplification of (CA)n repeats. The sizes of the amplified DNA were 180–350 bp. These specific sequences are given at the side of (CA)n repetitive sequence. ( B ) Amplified DNA fragments containing different (CA)n repeat numbers. An increase or decrease in the (CA)n repeat number brings about a change in the size of the PCR product directly.