Mitochondrial Genome Variations in Advanced Stage Endometriosis: A Study in South Indian Population

<div><h3>Background</h3><p>Endometriosis is a chronic gynecological benign disease that shares several features similar to malignancy. Mitochondrial DNA (mtDNA) mutations have been reported in all most all types of tumors. However, it is not known as to whether mtDNA mutations are associated with endometriosis.</p> <h3>Methodology</h3><p>We sequenced the entire mitochondrial genome of analogous ectopic and eutopic endometrial tissues along with blood samples from 32 advanced stage endometriosis patients to analyze the role of somatic and germ-line mtDNA variations in pathogenesis of endometriosis. All ectopic tissues were screened for tumor-specific mtDNA deletions and microsatellite instability (MSI). We also performed mtDNA haplogrouping in 128 patients and 90 controls to identify its possible association with endometriosis risk.</p> <h3>Principal Findings</h3><p>We identified 51 somatic (novel: 31; reported: 20) and 583 germ-line mtDNA variations (novel: 53; reported: 530) in endometriosis patients. The A13603G, a novel missense mutation which leads to a substitution from serine to glycine at the codon 423 of ND5 gene showed 100% incidence in ectopic tissues. Interestingly, eutopic endometrium and peripheral leukocytes of all the patients showed heteroplasmy (A/G; 40–80%) at this locus, while their ectopic endometrium showed homoplasmic mutant allele (G/G). Superimposition of native and mutant structures of ND5 generated by homology modeling revealed no structural differences. Tumor-specific deletions and MSI were not observed in any of the ectopic tissues. Haplogrouping analysis showed a significant association between haplogroup M5 and endometriosis risk (<em>P</em>: 0.00069) after bonferroni correction.</p> <h3>Conclusions</h3><p>Our findings substantiate the rationale for exploring the mitochondrial genome as a biomarker for the diagnosis of endometriosis.</p> </div

Mitochondrial haplogroup distribution in endometriosis patients and controls¹.

1<p>Haplogroups observed = 39; ²Banferoni correction for <i>P</i>-value = 0.05/39 = 0.00128.</p

Somatic mtDNA mutations observed in Endometriosis patients¹.

1<p>Total number of mutations: 51; ²Novel mutations: 31, Reported mutations: 20;</p><p>Ref, Cambridge reference sequence; Bld, Blood; Eut, Eutopic endometrium;</p><p>Ect, Ectopic endometrium; F, Frequency of mutations; HM, Homoplasmic mutation;</p><p>HT, Heteroplasmic mutation; NPCR, Non Protein Coding Region;</p

The ‘A13603G’ mutation of ND5 gene.

<p>(A) Sequence analysis of ‘A13603G’ mutation using a forward primer. Homoplasmic wild (13603A) and mutant alleles (13603G) appear as single peaks whereas heteroplasmic allele (13603A/G) as double peak. Evolutionary conservation analysis of mutation is also shown. CT: Control, CS: Case, BLD: Blood, EUT: Eutopic endometrium, ECT: Ectopic endometrium; (B) Native structure of ND5 subunit: ‘serine 423’ is shown as a blue sphere; (C) Ramachandran plot showing the structural accuracy of native structure of ND5 subunit: all the amino acids are in the allowed region except proline and glycine; (D) Mutated structure of ND5 subunit: ‘glycine 423’ is shown as a green sphere; (E) Superimposition of native (green) and mutant (red) structures of ND5 subunit.</p

Novel missense mtDNA mutations observed in endometriosis patients¹.

1<p>Total number of mutations: 18; ²Germ-line mutations: 11, Somatic mutations: 7; ³Conservation; Ref, Cambridge reference sequence.</p><p>Bld, Blood; Eut, Eutopic endometrium; Ect, Ectopic endometrium; F, Frequency of mutations; PC, Poorly conserved; HC, Highly conserved; CN, Conserved.</p