Identification and characterization of the exon 7-9 duplication in OPA1 by MLPA. (A) Typical read out of the MLPA experiment of index patient (VIII-4) depicting a significant increase for the exon 8 and 9 probes. (B) Long distance PCR amplification with forward and reverse primer located both in exon 8 yielded a fragment of approximately 8 kb in affected family members only (line 1: patient A, line 2: patient B, line 3: not affected control, line 4: no template control). (C) Sequencing of the amplicon shown in (B) reveals the genomic breakpoint and demonstrates that exon 7 is duplicated as well. The numbers above the arrows give the genomic position (human genome assembly, build 36.3), black capital letters indicate retained sequences of intron 9-10 and intron 6-7, respectively, while small red letters show the deleted sequence portion. The underlined 3 nucleotides can be found as reminiscence of the deletion event.