The paleoepidemiology of Sacral Spina Bifida Occulta in population samples from the Dakhleh Oasis, Egypt

Spina bifida, the normal, the pathological and the in-between: first evidence from a forensic osteological collection

Spina bifida (SB), a rare congenital disorder, is often mentioned as an individualizing factor in Forensic Anthropology. A lack of empirical data regarding SB is noticed in the scientific literature. Moreover, within the scope of anthropological research on SB disparities in terminology, classification systems, and methodological approaches result in incomparable results. The wide range (1,2%-50%) of "spina bifida occulta" reported prevalences is a good example. This research aims to analyze and debate the standard diagnostic criteria of SB on human skeletal remains, and attempts to elaborate on an universal system, premised on the distinction between SB as a pathology, and cleft neural arch (CNA) as an anatomical variant, according to Barnes (1994, p. 360 [1). A study-base of 209 individuals (88 males; 121 females; 44-99 years old) from the 21st Century Identified Skeletal Collection from the University of Coimbra (CEI/XXI) was macroscopically analyzed, focusing on the sacrum and remaining vertebrae. Four individuals presented complete posterior opening of the sacral canal (2,6%[4/156]). The observed bone changes, combined with the analysis of the entire skeleton, indicate that CNA, rather than SB linked to a neural tube defect, is the most reliable explanation for these cases. Overall, CNA was observed on 11 skeletons (7.05% of 156). The viability and applicability of the developed methodology for the identification of SB/CNA in forensic and/or osteological contexts are discussed, as well as the possibility of a lower prevalence of SB occulta, in the general population, than speculated before. HIGHLIGHTS: • Spina bifida has been studied so far under different methodologies, classification systems and nomenclature, leading to unstandardized and incomparable data. • Spina bifida as a pathological manifestation of a neural tube defect, as opposed to cleft neural arch as a simple form of skeletal variation. • Both spina bifida and complete sacral cleft fit the criteria of an individualizing trait in Forensic Anthropology.

Sacral Spina Bifida Occulta: A Frequency Analysis of Secular Change

Substantial relaxation of natural selection beginning around 1900 changed the mutation/selec­tion balance of modern genetic material, producing an increase in variable anatomical structures. While multiple structures have been affected, the temporal increase in variations of the sacrum, specifically, ‘Sa­cral Spina Bifida Occulta,’ have been reliably demonstrated on a localised scale. Calculation of largescale frequency has been hindered by the localised nature of these publications, the morphological variability of this variation, and potential pathological associations, which have produced divergent classifications, and conflicting reported rates of occurrence. A systematic review of the reported literature was conducted to provide an objective analysis of Sacral Spina Bifida Occulta frequency from 2500 BCE to the present. This review was designed to compensate for observed inconsistencies in reporting and to ascertain, for the first time, the temporal trajectory of this secular trend. A systematic review of Sacral Spina Bifida Occulta lit­erature was conducted through the strict use of clinical meta-analysis criteria. Publications were retrieved from four databases: PubMed, Embase, the Adelaide University Library database, and Google Scholar. Data were separated into three historical groups, (1 = <1900, 2 = 1900 to 1980 and 3 = >1980), and frequency outcomes compared, to determine temporal rates of occurrence. A total of 39/409 publications were included in the final analysis, representing data for 16,167 sacra, spanning a period of 4,500 years. Statistically significant results were obtained, with total open S1 frequen­cy increasing from 2.34%, (79 to 1900CE), to 4.80%, (1900 to 1980CE) and to 5.43% (>1980CE). These increases were significant at p<0.0001, with Chi-squared analysis. A clear secular increase in the global frequency of Sacral Spina Bifida Occulta has been demonstrated from 1900 to the present. This research provides a novel and adaptable framework for the future assessment of variation distribution, with impor­tant implications for the fields of biological anthropology and bioarchaeology.