Thirty-three years of X-linked adrenoleukodystrophy diagnosis at a Brazilian reference center: diagnostic patterns and key findings.

X-linked adrenoleukodystrophy (X-ALD) is the most common peroxisomal disorder. Although the quantification of very long-chain fatty acids (VLCFA) is an old technique implemented to diagnose and monitor, the limited number of experienced clinical biochemists in this field and also the limited availability of technical resources have resulted in scarce reports on the prevalence of X-ALD in developing countries like Brazil. This retrospective cross-sectional study analyzed all records of Brazilian patients diagnosed with X-ALD in LAM/SGM/HCPA from November 1992 to June 2026. Plasma VLCFA levels were analyzed by GC at diagnosis, along with patients' symptoms and their country's geographical origin. This is the largest reported Brazilian cohort (N = 275), comprising the three clinical forms of the disease: Addison disease, adrenomyeloneuropathy and childhood cerebral. Plasma VLCFA levels were consistently elevated across all phenotypes, characterizing the diagnosis together with the clinical manifestations and age. CCALD was primarily characterized by neurodevelopmental regression, seizures, behavioral disturbances, and visual impairment, whereas AMN was mainly associated with progressive myelopathy, and adrenocortical insufficiency was the predominant clinical manifestation in AD. Family history was identified in 43.3% of patients, and the mean diagnostic delay was 2.4 years for CCALD and 7.7 years for AMN, highlighting the importance of early recognition and family screening. Therefore, a detailed description of the patient's clinical presentation is essential for the correct diagnosis and interpretation of biochemical tests. Professionals need to be alert to this disease, given that multidisciplinary care is required.