Safety and Pharmacodynamic Study of Sobetirome in X-Linked Adrenoleukodystrophy (X-ALD)

Subjects will have a screening visit within 6 weeks prior to the Baseline visit. At Baseline visit blood will be drawn and to establish baseline values for plasma and red blood cell (RBC) very long chain fatty acids (VLCFA; C22, C24, and C26). Subjects will receive an oral dose of 50 mcg sobetirome once daily for 14 days beginning on Day 1. Subjects will be kept in the clinic on Day 1 for 16 hours following their initial dose of sobetirome for repeat blood sampling for pharmacokinetic analysis. Subjects will return to the clinic on days 7, 15, 21 and 28 for blood collection for VLCFA measurements. On day 15, after safety assessment, subjects will receive an increased dose of 100 mcg and this dose will be continued once daily through Day 28. Subjects will continue to return to the clinic weekly for blood and urine collection and safety assessments. Subjects will return to the clinic on day 42 for an End of Study visit that will involve a final measurement of VLCFA and blood and urine safety labs to check for reversibility. Safety labs will include serum chemistry, free fatty acid profile, hematology, urinalysis, and thyroid function. Subjects will be monitored with ECGs, vital signs, physical exams and assessment of adverse events.