Possible Association of a Novel Missense Mutation A6375G in the MitochondrialCytochrome C Oxidase IGene with Asthenospermia in the Tunisian Population

Abstract

Cytochrome c oxidase encoded by multiple mitochondrial genes (COXI, COXII, and COXIII) and nuclear genes is an essential component of the mitochondrial respiratory chain that catalyzes the reduction of molecular oxygen by reduced cytochrome c. Subunits COXI and COXII of cytochrome c oxidase are known to play the most essential role in proton pumping and electron transfer. In this study we screened the somatic mitochondrial COXI gene of infertile men suffering from asthenospermia (n=34) in comparison to normozoospermic infertile men (n=32) and fertile men (n=100) from the Tunisian population. A novel homoplasmic missense mitochondrial mutation (m.6375A>G) was found in 5 asthenospermic patients (14%) but not in any of normozoospermic infertile men and fertile men. This mutation substituting the isoleucine at position 158 to valine in a highly conserved amino acid induces a reduction of the hydropathy index (from +1.920 to +0.239) and a decrease of the protein 3D structure number (from 50 to 26) as shown by PolyPhen bioinformatic program.

‘Infertile’ studies on mitochondrial DNA variation in asthenozoospermic Tunisian men

“…The articles published in 2012 [27] and 2013 [11] referred to the analysis of 66 patients, of which 32 were normospermic and 34 asthenozoospermic. In the 2013 article [11] , the authors also mentioned an age range for patients of 23–57 years.…”

“…It is however surprising that none of the articles mentioned this issue, therefore conveying the impression that in reality five different and independent cohorts were considered – one per article. It is also remarkable that only one article from 2013 [10] cited the 2012 article [27] (although not in regards to the cohorts), while there are no cross-references among the rest of the articles. This is most noteworthy if we consider that the aims of the five articles were exactly the same, and all of them were carried out on Tunisians.…”

“…Baklouti-Gargouri et al also mention in the different publications the use of a control group of fertile men in order to investigate the incidence of their candidate mutations in healthy individuals. The sample size for this control group is 100 in the three initial publications [10] , [11] , [27] ; it grew to 150 in Baklouti-Gargouri et al [12] , and for some unexplained reason, these controls were omitted in the last publication from 2014 [16] . Curiously, in this latter publication, the authors used their normospermic infertile men as controls.…”

“…Thus, there are some disconcerting issues in the five Tunisian studies. First, the articles published in 2012 [27] and 2013 [10] targeted COXI , the article from 2014 [12] only COXIII , while the other two articles targeted the COXI , COXII , COXIII , ATP6 , ATP8 , and CYTB genes ( Table S1 ). For instance, COXI was sequenced in four out of the five studies.…”

“…We reviewed five articles published by the same research group from Tunisia. These articles were published in 2012 [27] , 2013 [10] , [11] , and 2014 [12] , [16] . Note that one of the 2014 papers [16] was indexed in PubMed using the first names of the authors instead of the family names, but the authors are virtually the same and following the same order in the five publications.…”