Letter to the Editor

Human Biology, Dec 1992

By Nancy L. Segal, Published on 02/28/14

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Letter to the Editor

Letter to the Editor Nancy L. Segal Recommended Citation - Article 21 Follow this and additional works at: http://digitalcommons.wayne.edu/humbiol Letter to the E ditor Twinning and Pediatric AIDS: Alternative Explanations An elevated incidence of twins, compared with nontwins, among infants diagnosed with maternally transmitted acquired immunodeficiency syn­ drome (AIDS) has been reported ( Thomas et al. 1990 ). The possibility of more frequent drug use by mothers of multiples and greater suscep­ tibility of twins rather than singletons to HIV infection will be considered in future research by these investigators. Resolution of this observation might be further assisted by examining possible associations between the frequency of dizygotic (DZ) twinning, coital rates, time of conception, and marital status. Increased coital rate has been suggested as an explanation for in­ creased DZ twinning due to superfecundity, or fertilizations occurring on different occasions within a menstrual cycle ( James 1981 ). Increased coital rate has, furthermore, been offered as an explanation for increased DZ twinning following periods of sexual abstinence ( James 1981 , 1986) and increased DZ twinning among conceptions occurring during the early months of marriage (Bulmer 1959) . An increased rate of DZ twinning has also been reported among illegitimate births in Finland (Eriksson and Fellman 1967) . Illegitimate DZ twinning rates also exceeded legitimate DZ twinning rates in England and Wales (1962-1966), except for women under twenty years of age; a lower coital rate among young women with illegitimate pregnancies was suggested as an explanation ( James 1981 ). Finally, all twins in the study by Thomas et al. were nonwhite. An in­ creased rate of DZ twinning among black populations, relative to white and Oriental populations, has been well documented (Bulmer 1970) and may explain, at least in part, the high incidence of twinning among moth­ ers in the present sample. Mothers of DZ twins have been described as a “reproductive elite” in view of their reproductive success ( James 1981 ). Numerous factors (e.g., maternal height and weight, family history of twinning) have been associated with DZ twinning (Bryan 1983) . Greater menstrual regularity among mothers of unlike-sex (DZ) twins has been linked to relatively prompt conception, compared with other women (Philippe and Roy 1989) . The possible associations between DZ twinning and sexual practice may, however, be especially relevant to the excess twinning observed among HIV-infected mothers. In view of the foregoing, it is meaningful that five of the seven twin pairs for whom physicians provided impressions of zygosity were dizygotic; this information was unavailable for the three remaining twin pairs. [It should be noted, however, that physicians’ judgments of zygosity do not always agree with diagnoses based on ser­ ological analysis; see Segal (1984) ]. It is possible that the population of women infected with HIV includes twin-prone individuals whose fre­ quency and pattern of sexual activity enhance the likelihood of DZ tw in­ ning. Thomas et al. (1990 ) are, fortunately, pursuing prospective studies of women infected with HIV so that meaningful relationships between twinning and HIV can be identified in the near future. Accurate classi­ fication of affected twin pairs as monozygotic or dizygotic and infor­ mation on coital frequency will be critical additions to the database. The availability of this information may help to identify mothers and infants at high risk for susceptibility to HIV and may suggest appropriate interventions. N A N C Y L. SE G A L * Assistant Director, Minnesota Center for Twin and Adoption Research University of Minnesota Department of Psychology 75 East River Road Minneapolis, MN 55455 Literature Cited Bryan , E.M . 1983 . The Nature and Nurture o f Twins . London: Bailliere Tindall. Bulmer , M .G . 1959 . The effect of parental age, parity and duration of m arriage on the twinning rate . Ann. H um . Genet . 23 : 454 - 458 . Bulmer , M .G . 1970 . The Biology o f Twinning in M an . Oxford: Oxford University Press. Eriksson , A .W . , and J. Fellman . 1967 . Twinning and legitim acy . H ereditas 4 7 : 3 9 5 - 402 . Jam es , W .H . 1981 . Dizygotic twinning: Marital stage and status and coital rates . Ann. H um. Biol . 8 : 371 - 378 . Jam es , W .H . 1986 . Dizygotic twinning: Cycle day of insemination and erotic potential of Orthodox Jews. A m . J. H um . Genet . 39 : 542 - 544 . Philippe , P . , and R. Roy . 1989 . Conceptive delays of tw in-prone mothers: A dem ographic epidemiologic approach . H um . Biol . 61 : 599 - 614 . Segal , N .L . 1984 . Zygosity testing: Laboratory and the investigator's judgm ent . Acta Genet . M ed. Gemellol. 33 : 515 - 521 . Thom as , P .A ., S.J. Ralston , M. Bernard , R. W illiam s, and R. O ' Donnell . 1990 . Pediatric acquired immunodeficiency syndrome: An unusually high (...truncated)


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Nancy L Segal. Letter to the Editor, Human Biology, 1992, Volume 64, Issue 4,