title: A wide range of 3243A>G/tRNALeu(UUR) (MELAS) mutation loads may segregate in offspring through the female germline bottleneck.
abstract: Segregation of mutant mtDNA in human tissues and through the germline is debated, with no consensus about the nature and size of the bottleneck hypothesized to explain rapid generational shifts in mutant loads. We investigated two maternal lineages with an apparently different inheritance pattern of the same pathogenic mtDNA 3243A>G/tRNALeu(UUR) (MELAS) mutation. We collected blood cells, muscle biopsies, urinary epithelium and hair follicles from 20 individuals, as well as oocytes and an ovarian biopsy from one female mutation carrier, all belonging to the two maternal lineages to assess mutant mtDNA load, and calculated the theoretical germline bottleneck size (number of segregating units). We also evaluated "mother-to-offspring" segregations from the literature, for which heteroplasmy assessment was available in at least three siblings besides the proband. Our results showed that mutation load was prevalent in skeletal muscle and urinary epithelium, whereas in blood cells there was an inverse correlation with age, as previously reported. The histoenzymatic staining of the ovarian biopsy failed to show any cytochrome-c-oxidase defective oocyte. Analysis of four oocytes and one offspring from the same unaffected mother of the first family showed intermediate heteroplasmic mutant loads (10% to 75%), whereas very skewed loads of mutant mtDNA (0% or 81%) were detected in five offspring of another unaffected mother from the second family. Bottleneck size was 89 segregating units for the first mother and 84 for the second. This was remarkably close to 88, the number of "segregating units" in the "mother-to-offspring" segregations retrieved from literature. In conclusion, a wide range of mutant loads may be found in offspring tissues and oocytes, resulting from a similar theoretical bottleneck size.
authors.affiliation: Department of Neurology, Columbia University, New York City, New York, United States of America; Dipartimento di Scienze Chirurgiche e Morfologiche, University of Insubria, Varese, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pallotti
authors.affiliation: Dipartimento di Scienze Teoriche e Applicate, University of Insubria, Varese, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Binelli
authors.affiliation: Unità Operativa di Ginecologia e Fisiopatologia della Riproduzione Umana, Ospedale S.Orsola-Malpighi, University of Bologna, Bologna, Italy; Dipartimento di Scienze Mediche e Chirurgiche (DIMEC), University of Bologna, Bologna, Italy.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Fabbri
authors.affiliation: IRCCS Istituto delle Scienze Neurologiche di Bologna, Ospedale Bellaria, Bologna, Italy; Dipartimento di Scienze Biomediche e Neuromotorie (DIBINEM), University of Bologna, Bologna, Italy.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Valentino
authors.affiliation: Unità Operativa di Ginecologia e Fisiopatologia della Riproduzione Umana, Ospedale S.Orsola-Malpighi, University of Bologna, Bologna, Italy; Dipartimento di Scienze Mediche e Chirurgiche (DIMEC), University of Bologna, Bologna, Italy.
authors.forename: Rossella
authors.initials: R
authors.lastname: Vicenti
authors.affiliation: Unità Operativa di Ginecologia e Fisiopatologia della Riproduzione Umana, Ospedale S.Orsola-Malpighi, University of Bologna, Bologna, Italy; Dipartimento di Scienze Mediche e Chirurgiche (DIMEC), University of Bologna, Bologna, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Macciocca
authors.affiliation: IRCCS Istituto delle Scienze Neurologiche di Bologna, Ospedale Bellaria, Bologna, Italy; Dipartimento di Scienze Biomediche e Neuromotorie (DIBINEM), University of Bologna, Bologna, Italy.
authors.forename: Sabina
authors.initials: S
authors.lastname: Cevoli
authors.affiliation: IRCCS Istituto delle Scienze Neurologiche di Bologna, Ospedale Bellaria, Bologna, Italy; Dipartimento di Scienze Biomediche e Neuromotorie (DIBINEM), University of Bologna, Bologna, Italy.
authors.forename: Agostino
authors.initials: A
authors.lastname: Baruzzi
authors.affiliation: Department of Neurology, Columbia University, New York City, New York, United States of America.
authors.forename: Salvatore
authors.initials: S
authors.lastname: DiMauro
authors.affiliation: IRCCS Istituto delle Scienze Neurologiche di Bologna, Ospedale Bellaria, Bologna, Italy; Dipartimento di Scienze Biomediche e Neuromotorie (DIBINEM), University of Bologna, Bologna, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Carelli
mesh_terms: D004272:DNA, Mitochondrial / Q000235:genetics*; D005260:Female; D005854:Germ Cells; D006801:Humans; D017241:MELAS Syndrome / Q000235:genetics*; D008297:Male; D009154:Mutation; D010375:Pedigree
chemical_list: D004272:DNA, Mitochondrial