Disease Outcomes in Boys with ABCD1 Variants Identified by Newborn Screening for X-ALD

To determine whether boys with VUS detected through Newborn screening (NBS) for Adrenoleukodystrophy (ALD) develop adrenal insufficiency (aiALD) and cerebral ALD (cALD) at rates comparable to those with pathogenic variants, and to evaluate the relationship between C26:0-lysophosphatidylcholine (C26:0-LPC) levels and clinical outcomes.

We conducted a retrospective multicenter cohort study (2013-2025) across six US centers, including 201 males identified through NBS in 19 states. Variants were classified as pathogenic (n=65), likely pathogenic (n=45), or VUS (n=88). Primary outcomes were development of aiALD and cALD; secondary outcomes included C26:0-LPC levels. Statistical analyses included Kaplan-Meier, mixed-effects regression, and Cox models.

201 males with ABCD1 variants identified through NBS for ALD. Median age at last follow-up was 4.2 years (IQR 2.5-7.9). Overall, 26% developed aiALD (54% pathogenic, 16% likely pathogenic, 11% VUS), and 8% developed cALD (11%, 9%, and 4.5%, respectively). Pathogenic/likely pathogenic variants were associated with higher odds of aiALD than VUS (OR 5.8; 95% CI 2.16-15.58; p=0.001). At 150 months, 39% of individuals with pathogenic/likely pathogenic variants remained free of aiALD versus 85% with VUS. C26:0-LPC levels were higher in pathogenic variants and correlated with genotype (p=0.0006). Higher levels were associated with increased aiALD risk and earlier onset (HR 1.38 per 0.1 µmol/L; 95% CI 1.20-1.59; p<0.0001).

Boys with VUS had lower rates of aiALD and lower C26:0-LPC levels than those with pathogenic variants, although some developed disease. C26:0-LPC correlates with genotype and risk, supporting its role in variant classification and risk-stratified surveillance.

Newborn screening for X-linked adrenoleukodystrophy has increased identification of variants of uncertain significance, accounting for up to 50% of screen-positive cases in some states. These are often associated with borderline biomarker levels, and their natural history remains poorly understood.

Screen-positive individuals with VUS had substantially lower rates of disease onset than those with pathogenic variants. Newborn biomarker levels also correlated with variant pathogenicity and disease onset, which may aid future variant classification and risk stratification.