In order to determine the role of mitochondrial DNA mutations in thyroid tumorigenesis, Abu-Amero et al., (2005) sequenced the entire mtDNA from 24 thyroid tumor specimens and four thyroid cancer cell lines.  Somatic mutations were identified in 37% of primary thyroid carcinomas (PTC) and among 25% of multinodular hyperplasia cases.  Most mutations were nucleotide substitutions resulting in missense mutations.  Of these sequence variants, 14 were nonsynonymous and 36 were synonymous.  Two nonsynonymous variants were identified in the ND3 gene in both PTC and control samples.  In a later study, Abu-Amero et al. (2006) sequenced the entire coding region of mitochondrial DNA for 26 MTC patients and 119 normal population controls.  Of the MTC patients, 13 were sporadic, nine had MEN 2A, one had MEN 2B, and three had FMTC.  In 20 MTC samples, 41 nonsynonymous mutations were detected; nine were from sporadic MTC and 11 were from familial MTC and MEN2.  Also 15 synonymous mtDNA sequence variants were found in MTC samples, seven of them were novel. Twenty seven mutations were transversions; 22 nonsynonymous and six synonymous.  These transversion variants were only detected in FMTC/MEN2 while transition variants were mainly found in sporadic MTC cases.  An A>G transition mutation was found in the MT-ND3 gene with a possibility of affecting the protein structure or function.  None of the described mutations were present in the normal controls, suggesting that mtDNA mutations may be involved in MTC tumorigenesis and progression.  Abu-Amero and Bosley (2006) studied further the molecular and biological characteristics of mitochondria in patients with Leber hereditary optic neuropathy (LHON)-like optic neuropathies.  Thirty five patients (21 males and 14 females) and 159 matched controls from Saudi Arabia were included in this study.  Forty one non-synonymous mtDNA sequence variants were identified in LHON patients; 14 were pathogenic.  Of these variants, 21 were in complex I, seven in complex III, five in complex IV, six in complex V, one in tRNA glutamine, and one in 12S rRNA.  Similar to previous reports on mutation association with LHON, these mtDNA changes were transitions.  The A10398G nonpathogenic variant was found within the MT-ND3 gene.