AIMS: Chromodomain helicase DNA-binding protein (CHD) is a regulator of the 
chromatin remodelling process. The aim was to determine the CHD1, CHD2, CHD3, 
CHD4, CHD7, CHD8 and CHD9 mutational status of mononucleotide repeats in gastric 
and colorectal cancers with microsatellite instability (MSI).
METHODS AND RESULTS: The repeats were determined in 28 gastric cancers (GCs) 
with high MSI (MSI-H), 45 GCs with low MSI (MSI-L)/stable MSI (MSS), 35 
colorectal cancers (CRCs) with MSI-H and 45 CRCs with MSI-L/MSS by single-strand 
conformation polymorphism analysis. CHD4 and CHD8 expression was also examined 
in GCs and CRCs by immunohistochemistry. CHD1, CHD2, CHD3, CHD4, CHD7, CHD8 and 
CHD9 mutations were found in five, 19, three, five, seven, 10 and seven cancers, 
respectively. They were detected in MSI-H cancers, but not in MSI-L/MSS cancers. 
Loss of CHD4 expression was observed in 56.4% of the GCs and 55.7% of the CRCs, 
and loss of CHD8 was observed in 35.7% of the GCs and 28.6% of the CRCs. The 
cancers with CHD4 and CHD8 mutations showed loss of CHD4 and CHD8 expression, 
respectively.
CONCLUSIONS: Frameshift mutation and loss of expression of CHD genes are common 
in GCs and CRCs with MSI-H.These alterations might contribute to cancer 
pathogenesis by deregulating CHD-mediated chromatin remodelling.