Sirenomelia: A Review of European Prevalence Data and Epidemiological Analysis of 17 Cases Registered in Wales

Background Sirenomelia is a rare congenital condition most notably characterized by a single lower limb. Previous studies have suggested a prevalence of approximately 1 per 100,000 births. However, in Wales 17 cases were recorded between 1998 and 2016, suggesting a higher rate of sirenomelia in this country.Objectives This study compared current prevalence of sirenomelia in Wales with European data. This study further reviewed detailed time, place, and person data on sirenomelia cases in Wales to investigate possible causal factors.Method A retrospective cohort study from birth defect surveillance programs. Individual-level records for all welsh cases were examined for evidence of causal factors. Comparator data from other countries were obtained from EUROCAT (a European network of population-based registries for the epidemiological surveillance of congenital anomalies).Results European data from 24 national and regional registries of congenital anomalies included 97 cases of sirenomelia identified across 9.6 million births between 1998 and 2016, giving a prevalence rate of 1 per 100,000 (95% CI 0.83, 1.23). Five regions reported statistically significantly higher rates than that recorded across all registries, while one region reported a significantly lower rate. Small numbers of cases limit definitive statistical interpretation. Analysis of the Wales data did not identify common epidemiological factors between cases.Conclusions The contemporary prevalence of sirenomelia across Europe is consistent with earlier studies at approximately 1 per 100,000 births (95% CI 0.83, 1.23). However, there is greater variation between regions than would be expected by chance. There remains no definitive evidence for causal environmental factors.