PEX1 and leukodystrophy: Patients with milder forms of PEX1-mediated ZSD (PEX1-ZSD) can have normal intellect or mild cognitive deficiency, survive to adulthood, can be employed, and can live semi-independently or independently.7, 8, 9 In contrast, patients with intermediate severity have moderate cognitive delays, most develop adrenal insufficiency, and around 25% develop additional disabilities, including epilepsy and leukodystrophy.1