The Grey Zone Project: Risk-Based Classification of ABCD1 Variants in X-Linked Adrenoleukodystrophy.

Area of Science:

• Biochemistry
• Genetics
• Pediatrics

Background:

• Newborn screening (NBS) for X-linked adrenoleukodystrophy (ALD) identifies boys at risk for adrenal insufficiency (AI) and cerebral ALD (CALD).
• Variants of uncertain significance (VUS) in ABCD1 present challenges in risk assessment due to borderline biochemical markers and limitations of traditional classification methods.
• Age-dependent penetrance and broad phenotypic spectrum complicate accurate risk stratification for ALD.

Purpose of the Study:

• To develop and validate a risk-stratification framework for interpreting ABCD1 VUS identified through NBS.
• To improve the accuracy of ALD risk assessment by integrating biochemical and clinical data.
• To reduce false-positive NBS results and enhance personalized patient management.

Main Methods:

• Developed a receiver operating characteristic (ROC)-based risk-stratification framework prioritizing 95% sensitivity.
• Incorporated biochemical (LPC(26:0)) and longitudinal clinical data from 1627 controls and 196 ALD patients.
• Defined three pediatric risk categories: "no ALD" (<110 nmol/L LPC(26:0)), "lower-risk AI/CALD" (110-177 nmol/L), and "at-risk AI/CALD" (>177 nmol/L).

Main Results:

• Applied the framework to 108 samples with 51 unique ABCD1 VUSs.
• Reclassified 26 variants to "no ALD," 15 to "lower-risk AI/CALD," and 10 to "at-risk AI/CALD."
• The framework demonstrated improved specificity in NBS for ALD without compromising sensitivity.

Conclusions:

• The developed framework effectively reclassifies ABCD1 VUS based on biochemical risk profiles.
• This approach reduces unnecessary referrals, MRI surveillance, and parental anxiety.
• The evidence-based model offers a scalable solution for variant interpretation and personalized follow-up in ALD and similar disorders.