Objective: Plasma assay for very long- chain fatty acids has made it possibl e to perform large- scale screening of at- risk individuals to identify asympt omatic patients with X- linked adrenoleukodystrophy (X- ALD). We evaluated the burden of undiagnosed adrenal insufficiency in 49 such patients (age, 4.5 ± 3 .5 years). Study design: Serum adrenocorticotropic hormone (ACTH) and standard- dose ACTH stimulation test were performed at the baseline and followed prospect ively until initiation of adrenal replacement therapy (follow- up, 2 ± 1.7 ye ars). Results: At baseline, 39 (80% ) patients had impaired adrenal function, s erum ACTH levels were elevated in 34 (69% ) patients, and ACTH stimulation test was abnormal in 21(43% ) patients. There was a moderate association between Se rum ACTH and age at baseline, (r = 0.32, P = .05). By the end of follow- up, 86 % of patients had borderline or overt adrenal insufficiency (age of onset, 4.8 ± 3.7 years). Conclusions: We detected a high prevalence of unrecognized adre nocortical insufficiency in asymptomatic boys with X- ALD. It is known to be a frequent cause of morbidity and can be prevented by careful monitoring, early id entification of impaired adrenal reserve, and timely initiation of therapy. It m anifests early and before onset of neurologic symptoms, suggesting X- ALD as a candidate disorder for neonatal screening.
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