Letter to the Editor
Letter to the Editor
Nancy L. Segal
Recommended Citation
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Article 21
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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)