Does Down syndrome occur more frequently in mothers with advanced age for patients diagnosed at Rwanda Center for Medical Genetics?

Abstract

Background: Down syndrome is the most common chromosome abnormality among live born infants and the most frequent recognizable genetic cause of intellectual disability in all human ethnic groups across the world. Advanced maternal age has been identified as risk factor associated with underlying mechanism of chromosome 21 non-disjunction leading to trisomy 21, the most frequent form of Down syndrome. A shift to younger maternal age for Down syndrome births appreciated in some recent studies. Lack of sufficient research data in Sub-Saharan Africa black population, and the importance of Down syndrome pediatric patients diagnosed in Rwanda especially those born to young mothers has prompted us to conduct a research to verify the magnitude of maternal age effect as risk factor for Down syndrome pregnancy. Hypothesis: the maternal age at birth of infants with Down syndrome is different from the maternal age at childbirth in the Rwanda general population. Methods: A cross-sectional survey was conducted at the Rwanda Center for Medical Genetics. Cases of Down syndrome patients diagnosed over a period of more than 9 years from December 2006 till February 2016 were identified with respective maternal ages at the time of birth. Using Stata SE software version 13, the Wilcoxon signed rank test was applied to compare the maternal age for these patients with the reference median age from the 2010 Rwanda Demographic Health Survey (RDHS). Results: Of 320 patients diagnosed over this period, maternal age was recorded only for 286 patients, of them 276 patients had free trisomy 21 and the mean maternal age at which they were born was 34.6 years [95% CI: 33.8-35.5]. The z test statistic calculated at the reference median maternal age gave a p-value < 0.0001. Conclusion: the difference between maternal ages at birth of Down syndrome patients and childbirth in the Rwanda general population was statistically significant. Advanced maternal age was thus, until proven otherwise an important risk factor for Down syndrome births in Rwanda too.