Dermatopathological features and successful treatment with topical antioxidant for ichthyosiform lesions in Mitchell syndrome caused by an ACOX1 variant

Abstract Peroxisomal acyl‐CoA oxidase 1 (ACOX1), is a peroxisomal enzyme that catalyzes β‐oxidation of very‐long‐chain fatty acids (VLCFA). The gain‐of‐function variant p.Asn237Ser in ACOX1 has been shown to cause Mitchell syndrome (MITCH), a neurodegenerative disorder characterized by episodic demyelination, hearing loss, and polyneuropathy, through the overproduction of hydrogen peroxide. Only eight cases of MITCH have been reported. While all these patients experienced cutaneous abnormalities, detailed skin features and potential treatment have not been documented. Herein, we report two MITCH patients who harbored a de novo heterozygous variant p.Asn237Ser in ACOX1 and experienced progressive ichthyosiform erythroderma. Skin histopathology revealed hyperkeratosis and parakeratosis with focal hypogranulosis as well as dyskeratotic keratinocytes. Lipid accumulation in the epidermis was observed using Oil Red O staining. Both patients exhibited a remarkable response to treatment with the topical antioxidant N‐acetylcysteine (NAC), with Patient 1 achieving complete recovery after 3 months of consistent treatment. This study provides the first comprehensive description of the clinicopathological characteristics and effective treatment of skin lesions in MITCH patients. The successful treatment with topical NAC suggests excessive reactive oxygen species might play a significant role in the pathogenesis of skin lesions in MITCH.