Expression of 12 positional candidates for QTL affecting shell thickness at 53 wk of lay age (ST53) was investigated by real-time PCR in the distal part of chicken oviducts (uterus) with a forming eggshell. In the local chicken breed Green-legged Partridgenous, the complete cDNA CR523443 (ChEST985k21) was downregulated with ratio of means 0.49 (P < or = 0.01) in the group with low ST53 (248.6 +/- 16.62 microm) relative to the group with the highest ST53 (372.4 +/- 2.07 microm). Expression of this gene was highly correlated (0.85, P < or = 0.01) with shell thickness. No significant difference in expression between the 2 groups with thick (378.4 +/- 3.65 microm) and thin (227.8 +/- 8.99 microm) shell and no significant correlation of expression level with ST53 were detected in Rhode Island Red, which could be explained by strict selection to egg quality traits, including optimal shell thickness in this commercial layer breed. These data suggested that CR523443 was a candidate gene for QTL ST53 in the chicken.