In contrast to adult AMN patients with ongoing myelopathy and progressive axonal damage, blood NfL levels in yet asymptomatic X-ALD children/adolescents were not significantly different from healthy controls with comparable age distribution (4.2 [3.3–4.9] vs 4.8 [3.6–6.3] pg/mL; model estimate of mean ratio: 1.62, CI: 0.71–3.66; adj. The gene discussed is NEFL; the disease is adrenomyeloneuropathy.