The last Neanderthals are believed to have lived around 40,000 years ago and yet there is an element of their DNA still lingering in some modern day humans, and it’s causing a rare, but sometimes fatal, medical condition. According to a new study led by researchers at B.C.’s Simon Fraser University, interbreeding between humans and their ancient cousins is the reason behind a neurological condition believed to be affecting up to one per cent of the population, named Chiari Malformation Type 1. The study, published in June in the journal Evolution, Medicine, and Public Health, describes how the rare condition occurs when the human skull is too small, and the cerebellum – a crucial part of the brain located at the back of the head responsible for co-ordination, balance and posture – is pushed through a small hole in the skull. “Part of the brain herniates down into the spinal canal, and then that causes a pinching of the spinal cord, a pinching of the cerebellum,” says the study’s co-author, and SFU postdoctoral fellow, Kimberly Plomp. The defect is so subtle that it is not something that can be seen by looking at somebody, but the consequences it produces can be devastating. “It can cause headaches, dizziness and numbness if it’s a small herniation,” says Plomp. “If it’s a large herniation, it can even be incompatible with life. It could cause death in juveniles.” Combining fossil data with information garnered from CT scans of people currently living with the condition, researchers were able to compare the shape of modern day skulls to those two million years old. “Essentially, what we found was that humans with this malformation have more similarities and shapes in their skull, especially in the back bottom bit of their skull, with Neanderthals than they do the humans without the malformation,” says Plomp. “This really highlights the fact that what we identified in humans with Chiari Malformation are traits that seem to be uniquely influenced by, what we think is, Neanderthal DNA.” According to Plomp, any modern humans with ancestry outside of Africa today has anywhere between two to five per cent of Neanderthal DNA in their genetic code, derived from the interbreeding that occurred thousands of years ago. Plomp says the research does little in the way of progressing treatment, which is already “pretty simple” and sees a neurosurgeon open up the hole in the skull to enable more space, which results in less pinching. But it does lead to an overall better understanding, an evolutionary explanation, as to why humans bear this condition. While the knowledge that ancient human ancestors interbred with Neanderthals is not new, the impacts of such mating is only now being researched and understood. Plomp says she hopes the study’s findings give way to further research in the future. For the next step, she hopes to conduct DNA analysis to identify the area of genetic code influencing the shape of the skull that leads to the Chiari Malformation, which could aid in potentially identifying people who might have the condition further down the road. “If we get to the point that we can identify people at risk of these conditions beforehand, then doctors can start making plans ahead of time before it becomes a health issue,” she says.
