Main findings
This is the first study showing that shortening of maternal TL per standard deviation decrease is associated with an almost 30% increased risk of VSD in offspring that attenuated to 25% after adjustment for maternal age (adjOR 1.25 (95% CI 1.01-1.55), p= 0.04). Moreover, we demonstrated a significant association between shorter maternal TL and the non-syndromal VSD group (crude OR 1.29 (95% CI 1.02-1.66), p=0.04), where after adjustment the association remained, but lost significance.
Strengths and limitationsOne of the main methodological strengths of this study is the use of the standardized samples taken approximately 1 year after the periconception period of the index pregnancy, which minimizes recall bias. Moreover, we prevented misclassification of cases and controls, given that most CODs are diagnosed during the first year of life. Another strength is the detailed description of the neural crest-related COD phenotypes and the ethnic homogeneity of case and control families. Another strength is the stratification in syndromes. As COD as part of a syndrome is more likely to be due to chromosomal abnormalities. A limitation of our study could be the measurement of TL in blood, which may not be representative for TL in the maternal oocytes or embryonic cardiac cells. However, it has been shown that leukocyte TL is highly correlated with TL of other somatic tissues from the same individual such as muscle, fat, skin and synovial tissue. This indicates that a clear intra-individual synchronization in TL exists in adults,(19) suggesting blood cell TL to be a valid measurement. Mean TL is measured, while cell senescence seems to be related to the shortest TL per cell.(20) A limitation of our study is that there are more typical COD types such as arterial trunk and double outlet right ventricle. The representation of these group were low in our study population and we were most interested in the VSD group as this was our largestgroup ofthe HAVEN study and most common phenotype of COD.
Interpretation
Our data support our hypothesis of using TL as biomarker for multiple exposures of oxidative stress and inflammation to assess the risk of COD offspring in the future. However, maternal age is the strongest determinant in this association. Thereby, the intricacy of TL translates in a high inter-individual variability, when comparing same-aged people.(21). This may be an explanation for the non-significant association found between TL and the risk of COD in general. Therefore, in future studies larger sample sizes are needed.
Previous studies in mice showed that, embryonic mice deficient in the telomerase gene show shorter TL and failure of closure of the neural tube as the main defect, suggesting that this developmental process is sensitive to telomere loss and chromosomal instability.(13, 22) These results support our findings, considering the similar risk factors neural tube defects and COD share. A hypothetical role of TL in neural tube defects (NTD) and COD is illustrated by the epidemiological and biological evidence of the association between hyperhomocysteinemia and increased risk of NTD and COD in offspring. (6, 13, 23). Hyperhomocysteinemia is a sensitive biomarker of oxidative stress and as such may reduce the synthesis or increase the damage of DNA, including the telomeres. The underlying mechanism could be impairment of the programming due to global or gene specific hypomethylation of telomerase. (24) In our study homocysteine was comparable between the groups, however homocysteine levels tended to be higher in cases. In our study population no correlation between homocysteine and TL was found. Thereby, adjusting for homocysteine concentrations had no significant influence on the association between TL and the risk of COD and or VSD offspring. Entringer et all. proposed that the effect of suboptimal intrauterine conditions on initial setting of TL and telomerase activity, is mediated by the programming actions of stress-related maternal-placental-foetal oxidative and metabolic pathways, in a way that accelerate cellular dysfunction, ageing and disease over the lifespan.(25) Embryogenesis in early pregnancy is sensitive to excessive oxidative stressors in the environment, resulting in structural and functional changes in cells, tissues and organ systems. Changes in TL of cells in the foetal heart may also play a role in normal cardiac development during embryogenesis and supports the association between TL and increased risk of VSD offspring.(26) The process of foetal programming of telomeres may reflect an effect shown across generations, that influences the health and well-being of not only individuals but also their offspring. Thereby, mother-offspring correlation in TL appears to be stronger than the father-offspring correlation, regardless of the gender of offspring.(27, 28) These finding emphasize the importance of efforts for early prediction and prevention.
Other associations between TL and obstetric outcomes have also been reported. Telomerase activity is decreased or absent in placentas of foetal growth restricted newborns.(29) In this way, foetal growth restriction is a common occurrence during COD pregnancies.(30)