Homozygous variant of MLC1 results in megalencephalic leukoencephalopathy with subcortical cysts.

Background: Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare, inherited disorder that causes epilepsy, intellectual disorders, and early onset macrocephaly. MLC1 has been identified as a main pathogenic gene. Methods: Clinical data such as magnetic resonance imaging (MRI), routine blood tests, and physical examinations were collected from proband. Trio whole‐exome sequencing (WES) of the family was performed, and all variants with a minor allele frequency (<0.01) in the exon and canonical splicing sites were selected for further pathogenic evaluation. Candidate variants were validated using Sanger sequencing. Results: Here, we report a new homozygous variant identified in two children from the same family in the MLC1 gene [NM_015166.4: c.838_843delinsATTTTA, (p.Ser280_Phe281delinsIleLeu)]. This variant is classified as variant of uncertain significance (VUS) according to the ACMG guidelines. Further experiments demonstrate that the newly identified variant causes a decrease of MLC1 protein levels when expressed in a heterologous expression system. Conclusion: Our case expands on this genetic variation and provides new evidence for the clinical diagnosis of MLC1‐related MLC. [ABSTRACT FROM AUTHOR]