Chiari Malformation and Human Evolution
Research type
Research Study
Full title
Evolution, cranial shape, and health: Using 3D geometric morphometrics to investigate the possible evolutionary origins of Chiari malformations
IRAS ID
264055
Contact name
Kanna Gnanalingham
Contact email
Sponsor organisation
Salford Royal NHS foundation trust
Duration of Study in the UK
2 years, 0 months, 0 days
Research summary
Chiari malformation (CM) is a developmental condition in which brain tissue herniates through the hole in the base of the skull (foramen magnum) into the spinal canal. Chiari malformation type 1 (CM-1) the most common form of the disease affects up to 1% of the population and can lead to a constellation of symptoms in affected patients but the cause behind this condition is not yet fully understood. Imaging studies in patients with CM have consistently demonstrated decreased volume in the posterior fossa, the space at the back of the skull, relative to the brain contents but the reason why this brain–skull volume mismatch occurs is currently unknown. One possible explanation put forward by previous authors is that CM may have an evolutionary origin. In particular it has been hypothesised that interbreeding between modern Homo sapiens and other Pleistocene hominin species such as Neanderthals has resulted in the presence of archaic genes within the human genome that result in a ‘brain-braincase’ mismatch within some randomly affected individual. To date, however, there have been no investigative studies to support this. The objective of this study is to undertake a comparative analysis of skull shape traits in patients with and without CM using previously acquired clinical CT and/or MR imaging. This imaging data will be analysed use a technique called geometric morphometrics (GM), which is increasingly recognized as useful scientific tools in clinical research and which utilises a powerful suite of tools that can identify subtle skull shape variation within and between organisms. Through this technique, it is hoped that we will not only identify the key cranial shape traits associated with Chiari type I malformation in affected patients but also identify the key differences and similarities in cranial shape between modern humans with CM and previously analysed Pleistocene hominin fossils.
Summary of Results
Aims: To identify through analysis of previously acquired clinical CT imaging data and previously collected Pleistocene hominin (early human ancestor) crania fossils what the key cranial shape traits associated with the presence of Chiari malformations (CM) in adults are; and the differences and similarities in cranial shape between modern humans with or without CM and Pleistocene hominin fossils.Background: Chiari malformation (CM) is a developmental condition in which brain tissue herniates through the hole in the base of the skull (foramen magnum) into the spinal canal. Chiari malformation type 1 (CM-1) the most common form of the disease affects up to 1% of the population and can lead to a constellation of symptoms in affected patients but the cause behind this condition is not yet fully understood. Imaging studies in patients with CM have consistently demonstrated decreased volume in the posterior fossa, the space at the back of the skull, relative to the brain contents but the reason why this brain–skull volume mismatch occurs is currently unknown. One possible explanation put forward by previous authors is that CM may have an evolutionary origin. In particular it has been hypothesised that interbreeding between modern Homo sapiens (humans) and other Pleistocene hominin species (early human ancestors) such as Neanderthals has resulted in the presence of genes within the human genome that result in a ‘brain-braincase’ mismatch within some randomly affected individual. To date, however, there have been no investigative studies to support this. The objective of this study is to undertake a comparative analysis of skull shape traits in patients with and without CM using previously acquired clinical CT imaging. This imaging data will be analysed use a technique called geometric morphometrics (GM), which is increasingly recognized as useful scientific tools in clinical research and which utilises a powerful suite of tools that can identify subtle skull shape variation within and between organisms. Through this technique, it is hoped that we will not only identify the key cranial shape traits associated with Chiari type I malformation in affected patients but also identify the key differences and similarities in cranial shape between modern humans with CM and previously analysed Pleistocene hominin fossils.
Methods: Clinically acquired pre-operative CT imaging was used to generate 3D skull reconstructions. 3D shape features were captured from these models using analyses, and this data was evaluated to see if patterns of shape variation correlated with the presence or absence of Chiari malformation type I (CM-I). These shape measurements were then compared with measurements undertaken on 11 fossil specimens (skulls) from human’s evolutionary ancestors (early Homo sapiens, Homo sapiens neanderthalensis, Homo erectus, and Homo. heidelbergensis) to identify similarities in skull shape between modern humans (with or without CM-I) and these early ancestor specimens.
Key findings: Significant shape trait differences associated with the Chiari malformation included smaller skulls; flatter occipital bones and a shorter basiocciput. Statistical analysis of acquired shape features demonstrated that humans with the Chiari malformation have skull shapes closer to Neanderthals and H. heidelbergensis than modern humans without the Chiari malformation. These preliminary results provide support for the theory that the Chiari malformation may relate in some cases to the retention of genes from early human ancestors coding for skull development. Further dedicated genetic studies are required to investigate this exciting finding further.
REC name
South Central - Hampshire A Research Ethics Committee
REC reference
19/SC/0341
Date of REC Opinion
2 Aug 2019
REC opinion
Further Information Favourable Opinion