Plasma neurofilament light chain as a biomarker for Fatal Familial Insomnia

BACKGROUND

Fatal Familial Insomnia is a rare hereditary prion disease associated with the D178N-129M PRNP mutation. Early diagnosis is difficult because the clinical syndrome may overlap with affective disorders. In addition, most known cerebrospinal fluid biomarkers for prion diseases and magnetic resonance imaging do not show a good diagnostic accuracy for Fatal Familial Insomnia. In this context, data on plasma biomarkers are scarce.

METHODS

We analyzed levels of neurofilament light chain, glial fibrillary acidic protein, chitinase-3-like protein 1, calcium-binding protein B, and total Tau protein in six serial plasma samples from a patient with Fatal Familial Insomnia. Subsequently, plasma neurofilament light chain was analyzed in n=25 patients and n=19 controls. The diagnostic accuracy and associations with disease stage and duration were explored.

RESULTS

Among all biomarker candidates in the case study, only neurofilament light chain levels showed a constant evolution and increased over time. It discriminated Fatal Familial Insomnia from controls with an area under the curve of 0.992 (95%CI:0.974 to 1) in the case-control study. Higher concentrations were associated with methionine homozygosity at Codon 129 PRNP (p=0.006), shorter total disease duration (rho=-0.467, p=0.019, 95%CI:-0.790 to -0.015), and shorter time from sampling to death (rho=-0.467, p=0.019, 95%CI -0.773 to -0.019).

CONCLUSION

Plasma neurofilament light chain may be a valuable minimal-invasive diagnostic biomarker for Fatal Familial Insomnia after clinical onset. Most important, stage-related increase and association with disease duration indicate potential as a prognostic marker and as a surrogate marker in clinical trials.

A review of drug therapy for sporadic fatal insomnia

BACKGROUND

Sporadic fatal insomnia (sFI) is a rapid progressive neurodegenerative disease characterised by gradual to perpetual insomnia, followed by dysautonomia, coma and death. ¹ The cause of sFI was recently mapped to a mutation in a protein, the prion, found in the human brain. It is the unfolding of the prion that leads to the generation of toxic oligomers that destroy brain tissue and function. Recent studies have confirmed that a methionine mutation at codon 129 of the human Prion is characteristic of sFI. Current treatment slows down the progression of the disease, but no cure has been found, yet.

METHODS

We used Molecular Docking and Molecular Dynamics simulation methods, to study the toxic Fatal-Insomnia-prion conformations at local unfolding. The idea was to determine these sites and to stabilise these regions against unfolding and miss-folding, using a small ligand, based on a phenothiazine "moiety".

CONCLUSION

As a result we here discuss current fatal insomnia therapy and present seven novel possible compounds for in vitro and in vivo screening.

Ethics in prion disease

This paper is intended to discuss some of the scientific and ethical issues that are created by increased research efforts towards earlier diagnosis, as well as to treatment of, human prion diseases (and related dementias), including the resulting consequences for individuals, their families, and society. Most patients with prion disease currently are diagnosed when they are about 2/3 of the way through their disease course (Geschwind et al., 2010a; Paterson et al., 2012b), when the disease has progressed so far that even treatments that stop the disease process would probably have little benefit. Although there are currently no treatments available for prion diseases, we and others have realized that we must diagnose patients earlier and with greater accuracy so that future treatments have hope of success. As approximately 15% of prion diseases have a autosomal dominant genetic etiology, this further adds to the complexity of ethical issues, particularly regarding when to conduct genetic testing, release of genetic results, and when or if to implement experimental therapies. Human prion diseases are both infectious and transmissible; great care is required to balance the needs of the family and individual with both public health needs and strained hospital budgets. It is essential to proactively examine and address the ethical issues involved, as well as to define and in turn provide best standards of care.