Loss of heteroplasmy in the displacement loop of brain mitochondrial DNA in astrocytic tumors

The aim of this study was the determination of D-loop heteroplasmy in astro cytic brain tumors. DNA fragments corresponding to the hypervariable region 2 of the mitochondrial displacement loop (D-loop) from 12 astrocytic tumor s and 2 corresponding brain samples were cloned into a plasmid vector. Hete roduplex analysis revealed high sequence variability in the brain samples a nd a subfraction of grade 2 and grade 3 tumors. Furthermore, the results we re suggestive of a very low degree of heteroplasmy in all glioblastomas. Th is was confirmed by direct sequencing of 223 cloned DNA samples from nine i ndividuals. Heteroplasmy was caused in most cases by a well-known length po lymorphism of a homopolymeric c-tract. Heteroplasmy of the two reference br ain samples was lost in the corresponding tumors. (C) 1999 Wiley-Liss, Inc.