[Analysis of a child with megalencephalic leukoencephalopathy with subcortical cyst type 2B caused by HEPACAM variant].

To explore the clinical features and genetic variant in a child featuring megalencephalic leukoencephalopathy with subcortical cyst (MLC) type 2B.Clinical and imaging data of the child was collected. Potential variant of hepatocyte adhesion molecule (HEPACAM) gene was detected by Sanger sequencing. The growth and development of her mother and uncle was also reviewed.The patient, a 1-year-and-7-month female, presented with convulsion, mental retardation and abnormally increased head circumference. Cranial MRI revealed extensive long T1 long T2 signals in the white matter of bilateral cerebral hemisphere, right anterior sac cyst, cerebral gyrus widening, and shallow sulcus. Sanger sequencing identified a c.437C>T missense variant in exon 3 of the HEPACAM gene. The same variant was detected in her mother but not father. Her mother and maternal uncle both had a history of increased head circumference when they were young. In their adulthood, the head circumference was in the normal range but still greater than the average.The heterozygous variant of the HEPACAM gene probably underlies the MLC2B in this child. The variant has derived from her asymptomatic mother, which suggested incomplete penetrance of the MLC2B.