Letter to the Editor

Heteroallelic Twins and Twin Publications

La parfaite raison fuit toute extremite,et veut que l’on soit sage avec sobriete.

—Moliere, Le Misanthrope, 1666

To the Editor:

In their recent Letter to the Editor concerning het-eroallelic twins and triplets, Cantu et al. [1998] pre-sented a composite figure without appropriate copy-right release required for republication of a previouslypublished figure [Dıaz-Gallardo et al., 1995]. Althoughthis duplicate publication may be disregarded as insig-nificant, it further extends the unethical procedurepreviously documented for the 1995 paper by the saidauthors [Rivera, 1996]. Altogether, these practices canbe regarded as scientific misconduct according to “theprinciple that scientists be truthful and fair in the con-duct of research and the dissemination of its results”[Ryan, 1996].

I am aware that whistleblowers are too easily dis-criminated against and condemned to ostracism; yet, Istill think that proper scientific behavior should be asine qua non condition for any researcher, especiallyfor an influential senior author who, among other hon-orary responsibilities, is a member of the EditorialBoard of the Mexican journal Archives of Medical Re-search (where the said 1995 paper was published). Bythe way, such a kind of incongruence was recentlyworded as follows: “Most important, do the [ethical]rules apply to everyone in your environment or only tothe students?” [Gunsalus, 1997].

Moreover, there are some other flaws in the Cantu etal. letter:

1. To refer to the skewed X inactivation in one of mono-zygotic twin females with Duchenne muscular dys-trophy [Zneimer et al., 1993] as a report “in whichthe assumption of the origin of the second amplifi-cation was based on a postzygotic event” (my italics)is nonsensical and out of context since there is notriplet amplification in the DMD gene.

2. The search for discordance in the number of CGG

repeats to document a prezygotic origin based on ahalf-chromatid mutation in the set of triplets seemsgroundless since the authors realize that “in MZtwins . . . there is no evidence to support such [aprezygotic origin].”

3. To affirm that MZ twinning “has at least two otherforms, homoallelic and heteroallelic, that can haveeither a prezygotic or a postzygotic origin” is merespeculation since Cantu et al. [1998] recognize thelack of evidence to support a prezygotic origin forMZ twins (see above); how a prezygotic origin can besuspected in homoallelic MZ twins escapes mycomprehension as there is no mutation clue to lookfor.

4. The closing remark, based on the known genes withtriplet repeat instability, that “genomically speak-ing . . . there are no identical twins” is untenable aseven MZ twins ascertained via the fragile X syn-drome often have an identical number of triplets[Kruyer et al., 1994] and because no references aregiven of MZ twins discordant for the number of trip-lets in other genes.

To conclude, I paraphrase the jargonaut’s statementto say that literally speaking there are no identicaltwin publications.

REFERENCESCantu JM, Dıaz-Gallardo MY, Barros-Nunez P, Figuera LE. 1998. Hetero-

allelic monozygotic twins and triplets. Am J Med Genet 77:166–167.

Dıaz-Gallardo MY, Barros-Nunez P, Dıaz CA, Hernandez A, Gomez-Espinel I, Leal C, Fragoso R, Figuera L, Garcıa-Cruz D, RamırezDuenas ML, Cantu JM. 1995. Molecular characterization of the fragileX syndrome in the Mexican population. Arch Med Res 26(suppl):S77–S83.

Gunsalus CK. 1997. Ethics: Sending out the message. Science 276:335.Kruyer H, Mila M, Glover G, Carbonell P, Ballesta F, Estivil X. 1994.

Fragile X syndrome and the (CGG)n mutation: Two families with MZtwins. Am J Hum Genet 54:437–442.

Rivera H. 1996. Fragile X studies and authorship. Arch Med Res 27:587–588.

Ryan KJ. 1996. Scientific imagination and integrity. Science 273:163.Zneimer S, Schneider N, Richards S. 1993. In situ hybridization shows

direct evidence of skewed X inactivation in one of monozygotic twinfemales with Duchenne muscular dystrophy. Am J Med Genet 45:601–605.

Horacio Rivera*Division de GeneticaCentro de Investigacion Biomedica de OccidenteInstituto Mexicano del Seguro SocialGuadalajara, Jalisco, Mexico

*Correspondence to: Horacio Rivera, Division de Genetica, Cen-tro de Investigacion Biomedica de Occidente, Instituto Mexicanodel Seguro Social, Ap. Postal 5-35, Gualdalajara, Jal., Mexico.E-mail: hrivera@udgserv.cencar.udg.mx

Received 18 September 1998; Accepted 10 March 1999

American Journal of Medical Genetics 86:88 (1999)

© 1999 Wiley-Liss, Inc.