Rare Gene Variants Linked to Spontaneous CSF Leaks

Spinal cerebrospinal fluid (CSF) leaks happen when there is a tear in the protective membrane around the brain and spinal cord which allows fluid to escape. These leaks can cause debilitating headaches and neurological dysfunction. Some patients develop spontaneous spinal cerebrospinal fluid leaks without any diagnosed connective tissue disorder, despite showing subtle or nonspecific signs of underlying tissue abnormalities. Researchers wanted to determine whether such unexplained cases might have a genetic basis.

One reason for this suspicion is that spontaneous CSF leaks are known to occur more frequently in people with genetic connective tissue diseases, such as Marfan syndrome and Loeys-Dietz syndrome. These disorders weaken connective tissue and increase the risk of tissue tears and ruptures, including CSF leaks. Roughly two-thirds of patients with spinal CSF leaks exhibit traits associated with a connective tissue disorder.¹ “Because some patients with unexplained spinal CSF leaks show subtle signs of connective tissue disease, even though they do not have a defined diagnosis, we sought to find a genetic cause,” said Wouter Schievink, a neurosurgeon at Cedars-Sinai Health Sciences University in a press release.

In their paper, published in The Lancet Neurology, the researchers used whole-exome sequencing and identified variants in the fibrillin 2 (FBN2) gene, which plays a role in maintaining tissue development and structural integrity.² When tested in human cell culture and animal models, these variants led to disruptions in adhesion to connective tissue and an increase in spinal lining tears and leaks, respectively. Together, these findings highlight the genetic contributors to spontaneous CSF leaks and may guide future diagnosis and treatments.

First, the researchers carried out whole-exome sequencing to look for a genetic cause within 42 people with unexplained leaks and more than 3,800 individuals without it. Of these, they focused on the type of spontaneous spinal CSF leaks which are associated with connective tissue disorders. They then narrowed their search to rare functional variants particularly expressed in the dura mater, the protective, outermost layer that envelops the brain and spinal cord. These rare mutations may be responsible for dramatically increasing the risk for leaks. In their search, the team identified 11 genes and found that the most frequent variants occurred in FBN2.

Then, the researchers tested cells that make up the protective layers surrounding the brain and spinal cord, specifically dural fibroblasts, and their binding capabilities to an extracellular matrix component that provides structural support to tissue. Cells with variants exhibited impaired binding compared to healthy control cells, suggesting that this could potentially weaken the protective connective tissue. Next, to test the functional effects of these variants, the team used CRISPR-Cas9 gene editing to generate mouse models with the different variants for spontaneous spinal CSF leaks and compared them to an established model for Marfan syndrome. The groups of mice carrying Fbn2 variants received an infusion of dyed water to identify whether a CFS leak occurred. These mice all had CSF leaks, indicated by a drop in pressure during infusion, further contributing to the evidence that these mutations increase the risk of CSF leaks.

“Potential future treatments can include medications that strengthen connective tissue or target the biological pathways affected by the FBN2 gene,” Schievink added.