Objective: To elucidate the structural polymorphism of EcoR I fragment within chromosomes 4q35 and 10q26 in the Chinese population and investigate the relationship of plasticity, translocation and somatic mosaicism in these domains with deletion of D4Z4 repeated units.
Methods: One hundred and ten unrelated healthy individuals from a random Chinese population were investigated. The genomic DNA was extracted from peripheral blood lymphocytes according to the specific procedure designed to minimize DNA shearing, then digested with EcoR I or double digested with EcoR I and Bln I. The cleaved DNA was separated by pulsed field gel electrophoresis (PFGE) and Southern blotted with the probe p13E-11. The sizes of EcoR I fragments were calculated by "curve fitting" according to the MidRange PFG marker and the alleles were assigned to their respective chromosomes based on their Bln I sensitivity. Data were analyzed using a commercially available statistical package (Version 11.0 SPSS).
Results: Seventy-seven point three per cent (85/110) of the unrelated healthy individuals displayed a standard configuration distribution. The mean and median of 4q35 repeat arrays are (87.9+/-3.3) kb and 78.5 kb respectively, whereas the mean and median of 10q26 homologous arrays are (90.1+/-4.1) kb and 73.0 kb. Repeat size distributions between both of them were of no significance according to the t test (P>0.05). 19.1% (21/110) of the individuals displayed a translocation repeat array configuration on chromosomes 4 and 10. No significant difference was detected between 4q-->10q translocation and 10q-->4q translocation according to Chisquare test (Chi2 test=0.053, P>0.05). Somatic mosaicism was observed in 3.6% (4/110) of the subjects and less than 35 kb 10-type array was found in 14.5% (16/110) of the individuals.
Conclusion: The structural polymorphism and dynamic behaviors of EcoR I fragments within 4q35 and 10q26 were demonstrated in this study using PFGE. The occurrence of frequent translocations and somatic mosaicism between 4q35 and 10q26 subtelomeric domains in the Chinese population further confirmed that mitotic interchromosomal gene conversion or translocation might be a major mechanism relating to the deletion of D4Z4 units.