Abstract
Cândido Godói (CG) is a small municipality in South Brazil with approximately 6,000 inhabitants. It is known as the “Twins' Town” due to its high rate of twin births. Recently it was claimed that such high frequency of twinning would be connected to experiments performed by the German Nazi doctor Joseph Mengele. It is known, however, that this town was founded by a small number of families and therefore a genetic founder effect may represent an alternatively explanation for the high twinning prevalence in CG. In this study, we tested specific predictions of the “Nazi's experiment” and of the “founder effect” hypotheses. We surveyed a total of 6,262 baptism records from 1959–2008 in CG catholic churches, and identified 91 twin pairs and one triplet. Contrary to the “Nazi's experiment hypothesis”, there is no spurt in twinning between the years (1964–1968) when Mengele allegedly was in CG (P = 0.482). Moreover, there is no temporal trend for a declining rate of twinning since the 1960s (P = 0.351), and no difference in twinning among CG districts considering two different periods: 1927–1958 and 1959–2008 (P = 0.638). On the other hand, the “founder effect hypothesis” is supported by an isonymy analysis that shows that women who gave birth to twins have a higher inbreeding coefficient when compared to women who never had twins (0.0148, 0.0081, respectively, P = 0.019). In summary, our results show no evidence for the “Nazi's experiment hypothesis” and strongly suggest that the “founder effect hypothesis” is a much more likely alternative for explaining the high prevalence of twinning in CG. If this hypothesis is correct, then this community represents a valuable population where genetic factors linked to twinning may be identified.
Highlights
The etiology of twin births in humans is still largely unclear and is the subject of a number of investigations [1,2,3,4]
It is noteworthy that while Linha Sao Pedro (LSP) contributes only 7.5% to all baptism records, it contributes almost 1/3 (33/92) to all twin births registered in Candido Godoi (CG), representing an odds ratio of 7.3 (CI 95% 4.75– 11.38) for LSP compared to the remaining districts in CG (P,0.0001) (Table 2)
There was no difference in maternal age between LSP and CG-LSP
Summary
The etiology of twin births in humans is still largely unclear and is the subject of a number of investigations [1,2,3,4]. MZ twins are developed when an embryo splits soon after fertilization. DZ twins occur when two separate oocytes, released during the same menstrual period, are fertilized by separate sperm cells [1]. MZ is rarer than DZ twinning except in Japan [5] and no maternal, genetic, or environmental factors have been associated to it so far [6]. DZ twinning is a phenomenon of complex etiology, in which both genetic predisposition and environmental factors play a role [7]. Non-genetic factors such as advanced maternal age, increased parity, lactation, diet, higher maternal height body mass index and race are observed as risk factors for DZ twinning too [11]
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