POLG exon 22 skipping induced by different mechanisms in two unrelated cases of Alpers syndrome.

The POLG genes were sequenced in two unrelated patients presenting with Alpers syndrome. The novel c.3626_3629dupGATA and the c.3643+2T>C alleles were associated in trans with p.A467T and p.[W748S;E1143G], respectively. POLG transcripts from skin fibroblasts showed complete exon 22 skipping for patient 2, but surprisingly partial exon 22 skipping from the c.3626_3629dupGATA for patient 1. The creation of a putative exonic splicing silencer could be responsible for the splicing anomaly observed in patient 1. Both c.3643+2T>C and c.3626_3629dupGATA create a premature termination codon and a low polymerase γ activity in skin fibroblasts is responsible for the severe phenotype in these patients.