Liquid biopsy for peripheral disease monitoring in X-ALD

The neurodegenerative disorder X-linked adrenoleukodystrophy (X-ALD) is the most common monogenetically inherited leukodystrophy affecting both children and adults. All X-ALD patients have mutations in the ABCD1 gene encoding a peroxisomal fatty acid transporter. Still, the disorder encompasses remarkably different phenotypes, ranging from a rapidly progressive cerebral inflammation resulting in premature death (cerebral ALD, CALD) to a milder non-inflammatory axonopathy involving the spinal cord and peripheral nerves (Adrenomyeloneuropaty, AMN). No genotype-phenotype correlation exists for the ABCD1 mutations in X-ALD. Accordingly, other genetic, epigenetic or environmental factors, or a combination thereof, are thought to trigger the brain inflammation in CALD. So far, the only treatment option for CALD is bone marrow transplantation or gene therapy involving genetically corrected bone marrow stem cells. However, these treatment regiments are only successful if CALD is recognized in its earliest stages. Although frequent conventional magnetic resonance imaging involving contrast agents is able to detect onset and progression of CALD, this method is associated with limitations as it does not directly report the degree of myelin loss and axonal injury. There is an urgent but currently unmet need for a sensitive, quantitative and easy accessible biomarker that would reveal the onset of CALD in its earliest stages and reflect the axonal damage in AMN patients. The aim of this project is to identify such a blood biomarker by focusing on two pathological key events in X-ALD: neuronal damage and oligodendrocyte cell death. Using blood samples from CALD and AMN patients as well as from healthy controls, we will apply state-of-the art molecular technology techniques like single-molecule array (SiMoA) and Next-Generation Sequencing to evaluate whether axonal damage or oligodendrocyte cell death is reflected by blood neurofilament light chain protein levels or the epigenetic status of cell free DNA. If successful, the results will have direct implications for clinical monitoring of X-ALD patients and for outcome measures in future clinical trials.

X-linked adrenoleukodystrophy (X-ALD) is a rare but severe inherited disorder of the nervous system that affects both children and adults. Although all patients carry mutations in the same gene (ABCD1), the clinical disease course is highly variable. While some patients develop only slowly progressive nerve damage, others suddenly experience severe inflammatory destruction of the brain's white matter (cerebral ALD, CALD), which is often fatal if left untreated. Currently, the only effective treatment for CALD-associated brain inflammation is stem cell transplantation or gene therapy, which can halt its progression, but they are only successful when applied at a very early stage. Clinical monitoring of patients currently relies mainly on MRI scans; however, this method often detects the disease only after significant brain damage has already occurred. Therefore, a simple blood-based biomarker that could indicate the early onset of brain inflammation has been lacking. The aim of this project was to identify such a blood biomarker. To this end, highly sensitive modern analytical technologies were used to examine blood samples from X-ALD patients and healthy controls. The focus was on the protein neurofilament light chain (NfL), a marker of nerve cell damage. Our results show that blood NfL levels reliably reflect the onset of brain inflammation in CALD. Importantly, elevated NfL levels can be detected before severe clinical symptoms or pronounced MRI abnormalities appear. A defined cut-off value allowed discrimination between X-ALD patients with and without early brain inflammation. In addition, NfL levels reflected the severity of brain injury and decreased again following successful treatment. Furthermore, the project generated first data exploring epigenetic signatures of cell-free DNA in blood as potential indicators of damage to nerve cells and oligodendrocytes. This opens a new approach for minimally invasive monitoring of myelin and neuronal injury in X-ALD patients. To summarise, NfL constitutes a promising minimally invasive biomarker that is able to significantly improve the clinical monitoring of X-ALD patients. It may help identify at-risk patients at an early stage, support therapeutic decision-making, and objectively measure treatment success. In the long term, these findings help to improve the prognosis of X-ALD patients and to design clinical trials more effectively.