Cell lineage involvement of the COX I mutation in patient no. 2. Total DNA was extracted from different types of cells: Bm, bone marrow; Bl, peripheral blood; Plt, platelets; B, B lymphocytes; T, T lymphocytes; Mu, buccal mucosa cells; SF, skin fibroblasts; Co, control bone marrow samples; lane 8, DNA size marker. In affected cell lineages, the COX I mutation creates a restriction site for Bsr I in the mtDNA segment nt 6504-6923, so that a considerable proportion of the 420-bp PCR product is cleaved into fragments of 243 and 177 bp.