Longitudinal Clinical Progression in X-Linked Adrenoleukodystrophy: The AMNL Scoring System

The current clinical nomenclature for individuals with ABCD1 gene dysfunction is often uninformative. The disorder was initially described as a combination of adrenal insufficiency and leukodystrophy, leading to the widespread use of "X-linked adrenoleukodystrophy" (ALD). However, this term is inaccurate for individuals who never develop these features. ABCD1 dysfunction can cause various symptom complexes: adrenal insufficiency, myelopathy, neuropathy, and leukodystrophy, which may occur consecutively, simultaneously, or not at all.

We developed an intuitive annotation system to precisely convey phenotype status for individuals with ABCD1 dysfunction. The "AMNL score" assesses the presence and severity of [A]drenal insufficiency, [M]yelopathy, [N]europathy, and [L]eukodystrophy, with scores ranging from 0 (no symptoms) to 3 (severe) per domain.

Applied to initial clinical encounters with 101 Dutch patients and 30 patients from the California newborn screening (NBS) program, the system identified 33 unique presentations. The most common was isolated mild myelopathy (A0M1N0L0). Including predominantly asymptomatic NBS newborns (mostly A0M0NUL0) broadened the spectrum and highlighted the need for precise classification across ages. Longitudinal use over 2 years in 99 Dutch patients showed progression in one or more domains in 41.4%, most often worsening myelopathy. In the NBS cohort (median follow-up: 3.5 years; range: 0.3-12.2), most patients showed no myelopathy or leukodystrophy, though adrenal involvement was detected in half. Initial inter-rater reliability was high (α = 0.996).

The AMNL score's ability to quantify domain-specific changes over time makes it valuable for monitoring disease evolution in clinical practice and research.