Newborn screening for ALD identifies boys with pathogenic ABCD1 variants early, enabling timely intervention. However, screening also reveals variants of uncertain significance (VUS) — genetic findings where it is unclear whether the variant will lead to disease. This creates significant diagnostic uncertainty for families and clinicians alike. In this podcast episode, Troy Lund and Stephan Kemp discuss how the Grey Zone Project addresses this challenge through a risk-based framework, and what it means in practice for families and clinicians navigating an inconclusive screening result.

Plasma NfL and GFAP levels were measured using highly sensitive Simoa technology, and patients were stratified based on their baseline levels. Men with high baseline NfL levels showed significantly faster worsening on disability and spinal cord outcome measures, with differences already apparent within the first year of follow-up. Importantly, plasma NfL levels remained stable over time, indicating that a single measurement has lasting predictive value. GFAP stratification, by contrast, showed limited prognostic utility on its own. Baseline plasma NfL is a robust and practical biomarker for identifying men with ALD who are at higher risk for faster spinal cord disease progression. This supports the use of NfL for patient stratification in future clinical trials, making those trials more efficient and better able to detect treatment effects.

After analyzing 1,627 healthy controls and 196 ALD patients with detailed clinical follow-up, we established evidence-based thresholds that classify variants into three clear categories: ‘no ALD’, ‘lower risk of childhood disease’ and ‘at risk of childhood disease’.
We applied this framework to 108 samples representing 51 unique VUSs.
🟢 26 VUSs were reclassified as ‘no ALD’.
🟡 15 VUSs were identified as ‘lower risk for childhood disease’.
🔴 10 VUSs were identified as ‘at risk of childhood disease’.
The Grey Zone Project aims to improve diagnostics. It’s also about providing families with clarity during critical moments, minimizing unnecessary medical interventions, and ensuring that children who require monitoring receive it.
All reclassification data feed back into the ABCD1 Variant Registry and ‘no ALD’ variants will be reclassified as ‘benign, confirmed by normal LPC(26:0) levels’.

The Results: The experts agreed on a core screening protocol for both adults and children that includes: ✅ 3D T1-weighted imaging, ✅ spin-echo T2-weighted imaging, ✅ 3D fluid-attenuated inversion recovery (FLAIR), and ✅ diffusion-weighted imaging (DWI).
Post-contrast T1-weighted imaging should be added in specific clinical scenarios. For monitoring lesion progression, the experts recommended using DWI alongside the Loes score and post-contrast imaging.
Why this matters: This harmonized protocol provides clinicians worldwide with a practical framework for screening and monitoring brain lesions in ALD, thereby improving clinical decision-making. It also identifies priority MRI sequences for future research, including diffusion tensor imaging, MR perfusion, and quantitative volumetric analyses. International collaboration through structured consensus-building is advancing standardized, evidence-based care for ALD patients.

The research revealed that ALD organoids display early and persistent accumulation of very long-chain fatty acids (VLCFAs), the hallmark of ALD. Remarkably, the lipid alterations observed in these laboratory-grown models closely mirror those found in actual ALD patient brain tissue, validating organoids as relevant models for studying disease mechanisms.
This work demonstrates the power of combining cutting-edge stem cell technology with advanced lipidomics analysis. By creating “mini-brains” from patient cells, we can now study how ALD develops at the molecular level in human tissue—something that would be impossible to do in living patients. These findings open new avenues for understanding early disease processes and testing potential treatments in a controlled, human-relevant system.
Read the full paper

His dissertation provides a translational approach to ALD, bridging fundamental insights into pathophysiology with direct clinical applications. The dissertation deepens our understanding of ALD pathology at the cellular level. It evaluates the hypothesis that axonal degeneration with secondary demyelination is central and proposes a comprehensive theory that highlights the understudied role of astrocytes. Quantitative MRI reveals early changes in tissue at the level of normal-appearing white matter, highlighting the significant involvement of axons and myelin. Lipidomics in plasma reveals distinct profiles in severely affected patients. Meanwhile, wearable accelerometers offer reliable outcome measures for spinal cord disease that correlate with fall risk and traditional disability scales. The research shows that patients with more severe baseline disease experience faster spinal cord deterioration—an important consideration for clinical trials. Finally, exploring attitudes toward newborn screening reveals that most patients favor screening both boys and girls, offering valuable guidance for future policy.
The promotors, Marc Engelen, Stephan Kemp, and Marjo van der Knaap, would like to thank the members of the thesis committee: Annet Bosch, Carla Hollak, Fanny Mochel, Liesbeth Reneman, Marianna Bugiani, and Marielle Brouwer for their insightful and engaging feedback.

The award supports young researchers who have recently graduated and are working on metabolic diseases. The prize is €320,000 for their projects. From 11 preliminary applications, three finalists were selected to submit a full proposal. Yorrick’s project, “ALD in 4D,” was unanimously rated excellent by international reviewers.

The project is developing a predictive test to determine which adrenoleukodystrophy patients, detected through early screening such as the heel prick test, will develop the fatal brain form so that life-saving treatment can start sooner and reduce uncertainty for families.

The impressive award ceremony was attended by Jelte’s family; parents of children with metabolic diseases; the mayor of Leeuwarden, Sybrand Buma; local media, including Omrop Fryslân, who interviewed Yorrick; the Metakids Scientific Advisory Board; and Metakids representatives.

The long drive back from Friesland could have been quiet and boring, but it was anything but. This recognition is wonderful for Yorrick, our Genetic Metabolic Diseases laboratory, and research into metabolic diseases.

Photos by Corien Steenstra

Yorrick’s work advances the diagnosis and understanding of X-linked adrenoleukodystrophy (ALD) by integrating targeted and comprehensive lipidomics. His research shows that analyzing LPC 26:0 is better than using traditional VLCFA measurement to diagnose ALD. It is faster, less labor-intensive, and more reliable, especially for women. Lipidomic profiling in plasma, cerebrospinal fluid, and cell models revealed that VLCFAs accumulate in distinct lipid classes, strongly correlating with disease severity in both sexes. This study identifies promising candidates and highlights the potential of advanced lipidomics and biobank resources for discovering future prognostic biomarkers and improving patient care.

We, the promotors Gajja Salomons, Marc Engelen and Stephan Kemp and the paranymphs Michel van Weeghel and Inge Dijkstra, would like to thank the members of the thesis committee: Annet Bosch, Anita Boelen, Judith Jans, Martin Giera,Troy Lund and Noam Zelcer for the inspiring and entertaining opposition.