Characterization of an MLC patient carrying two MLC1 variants showing radiological improvement

•Here, we identify a new MLC1 patient that show improvement over time, but that carry recessive mutations in MLC1.•Genetic and biochemical studies using peripheral blood leukocytes from the patient indicated that he expresses a small amount of MLC1.•We then suggest that a novel classification of MLC patients, adding a novel group named MLC1B.•We provide a molecular explanation for the reversibility of the phenotype found in some MLC patients, which has implications for MLC therapy.