It has been shown that aneuploidy,
the occurrence of abnormal chromosome numbers in a cell, contributes to
miscarriages and congenital abnormalities. While the causes are unknown, scientists have found that the problem occurs at nondisjunction during spermatogenesis, and suspect that environmental pollutants may play a large role in this.
In a recent journal article published in Environmental Health Perspectives, the authors aimed
to investigate whether environmental exposure to persistent organic pollutants,
specifically dichlorodiphenyldicholorethylene (p,p'-DDE) and
polychlorinated biphenyls (PCBs), were associated with sex-chromosome
disomy in men. To do so, they did a 22-year study on the males of the Faroe
Islands, which is a population exposed to above-average levels of
organochlorine pollutants due to their seafood-rich diet. They began with 747
Faroese men, 242 of which were part of a “birth cohort”, which consisted of
people born between 1986 and 1987 and had biological samples and information on physical health and environmental exposures
obtained at birth. They participated in follow-ups at age 14, and also agreed
to participate in studies of semen quality at age 22. Our of all 747 participants, 90 were then randomly selected as samples, in which 40 were birth cohort, 12 were fertile (fathers cohort), and 38 were randomly selected men. In addition, data on in utero exposures via cord blood
samples were available for 40 participants and at age 14 for 33 participants.
The study found that
both adult and age 14 DDE and PCBs serum concentrations were associated with
significantly increased rates of chromosomes XX18, XY18, and total disomy. But
cord blood concentrations were not significant with sperm disomy. There was also evidence of a negative association between DDE and YY18, but results for PCBs and YY18 were inconsistent.
In the popular media article from Scientific American, I was pleasantly surprised by their accurate reporting and concise usage of language. They made the science more readable and related the findings to how they can impact our lives, specifically sperm abnormality and governmental policies.
They gave a general overview of the study by stating the sample sizes and findings, but it did so selectively. It noted that the scientists "examined sperm and blood samples from 90 men from the Faroe Islands... [and] for 33 of the men, they also had blood samples at age 14". They failed to mention the three different "cohorts" that the scientists randomly selected these men from, and how they controlled for the experiment. The article also generalized the findings, saying that "men with higher levels of DDE... and... PCBs... at 14 years old had higher rates of abnormal sperm". It's important to remember that only specific aneuploidies were found, and that results for PCBs and YY18 was actually inconsistent.
I think they did well controlling for different variables. However, I think it would have been interesting if they also studied a group of males outside of the Faroe Islands. That way another control group could have been included in the data.
ReplyDeleteThe study mentions that non-persistent chemicals can impact sperm aneuploidy. It would have been interesting to look at other pollutants known to impact sperm viability, or at least to do an exposure assessment for some of the men to investigate whether they are exposed to other pollutants which may have reproductive impacts.
ReplyDeleteI enjoyed the Scientific American article. They represented the study accurately and I also thought that they did a good job incorporating relevant historical and background information (e.g. Rachel Carson's Silent Spring, and the chemical's high persistence). However, I believe stronger language could have used in stating: "The study doesn’t prove that the chemicals hamper sperm but both DDT and PCBs are known to disrupt the endocrine system." It's correct that it wasn't proved, but a significant association was observed.
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