Detection of a heteroplasmic mtDNA mutation in a bone marrow aspirate from patient no. 1. RFLP analysis of mtDNA segment 7 (nt 6504-7608) with Cfo I in four patients (lanes 1 through 4) and with Rsa I in the same four patients (lanes 6 through 9) showed an abnormal restriction pattern in patient no. 1 (lane 9); for explanation, see text. Lane 5, DNA size marker (pGEM).