On 2017 Oct 18, Nicoletta Villa commented:

1. The first question is: how to define this chromosome? It had a complete X banding exactly symmetrical above and below the primary constriction and presented an active centromere in an anomalous position definable as neocentromere, though canonical (repositioning).
2. According to the International System for Human Cytogenetic Nomenclature (ISCN) 2016, the definition of centric fission is: “break in the centromere resulting in two derivative chromosomes composed of the short and long arms, respectively”. This does not happen in the chromosome X here described since the whole chromosome (old centromere included) constitutes the isochromosome. This was also confirmed by the paracentric inversion that offers us a complicated but responsive mechanism for the isochromosome formation. Regarding the cited review (Lin and Yan, Mutat Res 2008; 658:95), we mentioned it in the introduction and discussion sections. In both cases, we reported general aspects of telomeric-like sequences. We speculated that the paracentric inversion of the entire Xp arm could be a result of a non-allelic homologous recombination mediated by inverted repeats, as reported by Warburton and Dittwald (see article for details). FISH data with pan-telomeric probes revealed the anomalous presence of TTAGGG repeats near the inactive centromeres in a highly symmetrical manner, absent in the Xp terminations. Therefore, we used BAC probes and identified the paracentric inversion of the entire short arm that made the telomere common sequences completely interstitial. Silahtaroglu et al (J Med Genet 1998; 35:682) reported a paracentric inversion that did not involve telomeric region in a XXY male (“Simultaneous hybridisation with biotin labelled "All Centromere" and digoxigenin labelled "All Telomere" probes showed that the telomeric sequences were not inverted). This is not our case.
3. Rivera et al. (Clin Genet 1999, 55:122) reported a case showing a rearrangement due to a centric fission of chromosome 12 and a translocation on chromosome 8p. This last rearrangement resulted in a fusion between 8ptel and 12cen mediated by interstitial telomeric sequences, as well written in the abstract. In our case there was not a fusion between two different chromosomes, but an isochromosome, confirmed by banding, FISH and by means of microsatellite segregation study. Moreover, we demonstrated the presence of telomeric sequences near to the old centromeres.
4. We did not perform the androgen receptor inactivation test because the itrc(X) was always inactivated in reverse banding (RBA) as it is possible to see in figure 1B and also the microsatellite polymorphisms never showed a third allele. Moreover, the mosaic situation made a quantitative analysis very difficult or even impossible due to the loss of Xq.
5. The frequency of chromosomal abnormalities in couples subjected to medically assisted procreation appears to be increased (literature data), but we couldn’t correlate the chromosomal rearrangement here described with PMA. We don’t know parental origin of the rearrangement and parents refused further analyses.

On 2017 Jul 19, Horacio Rivera commented:

Centromere repositioning or neocentromere in a tricentric X chromosome? As for the unique tricentric X-cromosome described by Villa et al. (2017), I do the following remarks: 1. The apparent discrepancy between title and content regarding the paper’s key concept illustrates how difficult is to classify the single functional centromere of the rearranged X: did it result from centromere repositioning and is a class III neocentromere as stated in the title or is it a novel kind of neocentromere? Since the former mechanism implies the emergence of a new non-alphoid centromere in otherwise intact chromosomes (Marshall et al. Am J Hum Genet 2008, 82: 261; Liehr et al. Cytogenet Genome Res 2010,128:189), it seems better to opt for the more general term neocentromere despite it being composed of alphoid sequences. 2. Since the authors plausibly ascribe the emergence of the functional centromere at an unexpected place to an initial paracentric inversion of the entire Xp arm “shifting a part of the centromere at the p end”, then they may have designated such centromeric breakage with the specific term centric fission. It is significant that the hypothetical telomere-like sequences mapping at Xp11.21 or 22 and thought by the authors to be involved in the rearrangement, are simply not referred to in the cited review (Lin and Yan, Mutat Res 2008; 658: 95); moreover, the authors appear to contradict themselves when they conclude that “the first event could be a result of a non-allelic homologous recombination mediated by inverted low-copy repeats”. Regardless of the concerned sequences, the exact breakpoint should be revised to Xp10 and the Xp rearrangement designated as a centric inversion after Silahtaroglu et al. (J Med Genet 1998, 35: 682) who described an inverted 12p resulting from a centric fission coupled with a subtelomeric breakpoint. 3. According to the underlying mechanism advanced by the authors, two true centromere-telomere fusions (Rivera et al. Clin Genet 1999, 55: 122) occurred in the rearranged chromosome. Yet, the authors also fail to recognize this phenomenon. 4. Despite the analysis of microsatellite polymorphisms, the parental derivation of the tricentric X chromosome was not determined. Likely, the HUMAR assay could have resolved this point. 5. The fact that the patient was conceived after intracytoplasmic sperm injection recalls other chromosome rearrangements and gonosomal aneuploidies found in children conceived by means of such a technique (Venkataraman and Craft, Hum Reprod 2002, 17: 2560; Alfonsi et al. Cytogenet Genome Res 2012, 36: 1; Rivera and Domínguez, Clinics 2012, 67: 669).

On 2017 Jul 19, Horacio Rivera commented:

Centromere repositioning or neocentromere in a tricentric X chromosome? As for the unique tricentric X-cromosome described by Villa et al. (2017), I do the following remarks: 1. The apparent discrepancy between title and content regarding the paper’s key concept illustrates how difficult is to classify the single functional centromere of the rearranged X: did it result from centromere repositioning and is a class III neocentromere as stated in the title or is it a novel kind of neocentromere? Since the former mechanism implies the emergence of a new non-alphoid centromere in otherwise intact chromosomes (Marshall et al. Am J Hum Genet 2008, 82: 261; Liehr et al. Cytogenet Genome Res 2010,128:189), it seems better to opt for the more general term neocentromere despite it being composed of alphoid sequences. 2. Since the authors plausibly ascribe the emergence of the functional centromere at an unexpected place to an initial paracentric inversion of the entire Xp arm “shifting a part of the centromere at the p end”, then they may have designated such centromeric breakage with the specific term centric fission. It is significant that the hypothetical telomere-like sequences mapping at Xp11.21 or 22 and thought by the authors to be involved in the rearrangement, are simply not referred to in the cited review (Lin and Yan, Mutat Res 2008; 658: 95); moreover, the authors appear to contradict themselves when they conclude that “the first event could be a result of a non-allelic homologous recombination mediated by inverted low-copy repeats”. Regardless of the concerned sequences, the exact breakpoint should be revised to Xp10 and the Xp rearrangement designated as a centric inversion after Silahtaroglu et al. (J Med Genet 1998, 35: 682) who described an inverted 12p resulting from a centric fission coupled with a subtelomeric breakpoint. 3. According to the underlying mechanism advanced by the authors, two true centromere-telomere fusions (Rivera et al. Clin Genet 1999, 55: 122) occurred in the rearranged chromosome. Yet, the authors also fail to recognize this phenomenon. 4. Despite the analysis of microsatellite polymorphisms, the parental derivation of the tricentric X chromosome was not determined. Likely, the HUMAR assay could have resolved this point. 5. The fact that the patient was conceived after intracytoplasmic sperm injection recalls other chromosome rearrangements and gonosomal aneuploidies found in children conceived by means of such a technique (Venkataraman and Craft, Hum Reprod 2002, 17: 2560; Alfonsi et al. Cytogenet Genome Res 2012, 36: 1; Rivera and Domínguez, Clinics 2012, 67: 669).

On 2017 Oct 18, Nicoletta Villa commented:

1. The first question is: how to define this chromosome? It had a complete X banding exactly symmetrical above and below the primary constriction and presented an active centromere in an anomalous position definable as neocentromere, though canonical (repositioning).
2. According to the International System for Human Cytogenetic Nomenclature (ISCN) 2016, the definition of centric fission is: “break in the centromere resulting in two derivative chromosomes composed of the short and long arms, respectively”. This does not happen in the chromosome X here described since the whole chromosome (old centromere included) constitutes the isochromosome. This was also confirmed by the paracentric inversion that offers us a complicated but responsive mechanism for the isochromosome formation. Regarding the cited review (Lin and Yan, Mutat Res 2008; 658:95), we mentioned it in the introduction and discussion sections. In both cases, we reported general aspects of telomeric-like sequences. We speculated that the paracentric inversion of the entire Xp arm could be a result of a non-allelic homologous recombination mediated by inverted repeats, as reported by Warburton and Dittwald (see article for details). FISH data with pan-telomeric probes revealed the anomalous presence of TTAGGG repeats near the inactive centromeres in a highly symmetrical manner, absent in the Xp terminations. Therefore, we used BAC probes and identified the paracentric inversion of the entire short arm that made the telomere common sequences completely interstitial. Silahtaroglu et al (J Med Genet 1998; 35:682) reported a paracentric inversion that did not involve telomeric region in a XXY male (“Simultaneous hybridisation with biotin labelled "All Centromere" and digoxigenin labelled "All Telomere" probes showed that the telomeric sequences were not inverted). This is not our case.
3. Rivera et al. (Clin Genet 1999, 55:122) reported a case showing a rearrangement due to a centric fission of chromosome 12 and a translocation on chromosome 8p. This last rearrangement resulted in a fusion between 8ptel and 12cen mediated by interstitial telomeric sequences, as well written in the abstract. In our case there was not a fusion between two different chromosomes, but an isochromosome, confirmed by banding, FISH and by means of microsatellite segregation study. Moreover, we demonstrated the presence of telomeric sequences near to the old centromeres.
4. We did not perform the androgen receptor inactivation test because the itrc(X) was always inactivated in reverse banding (RBA) as it is possible to see in figure 1B and also the microsatellite polymorphisms never showed a third allele. Moreover, the mosaic situation made a quantitative analysis very difficult or even impossible due to the loss of Xq.
5. The frequency of chromosomal abnormalities in couples subjected to medically assisted procreation appears to be increased (literature data), but we couldn’t correlate the chromosomal rearrangement here described with PMA. We don’t know parental origin of the rearrangement and parents refused further analyses.