Figure 4 Restriction analysis. Polyacrylamide gel with the MseI restriction analysis of the 13042G→A mutation. B, blood; U, urinary epithelium; M, skeletal muscle; C, control; U, uncut. The 216 base pair (bp) amplicon is cut into two fragments of 187 and 29 bp (not shown) in the presence of the 13042G→A mutation. In four cases the mutation was not detected in the blood but was present in the urinary epithelium (IV‐2, V‐6, IV‐11, and IV‐14). In the other four individuals the mutational load in the urinary epithelium was always strikingly higher than in blood (IV‐4, IV‐6, IV‐7, and V‐12). The two affected individuals (IV‐4 and IV‐7) had high mutant loads in the urinary epithelium and the proband showed over 90% mutant mtDNA in her skeletal muscle.