Frequency of focal granule cell bilamination (FGCB) in the dentate gyrus during first 18 months of life

To the Editor: The presence of focal granule cell bilamination (FGCB) within the dentate gyrus (DG) of the hippocampus has become a feature of interest within the clinical context of sudden unexpected deaths in infancy (SUDI), particularly for the group of infants in which the cause of death remains unexplained and fits the diagnostic classification of sudden infant death syndrome (SIDS).1 The interest into FGCB within SUDI stems from an initial study that identified FGCB in 33% of 153 SUDI infants, with the breakdown of 41.2% of SIDS compared to 7.7% of explained SUDI (eSUDI), suggesting an increase in incidence among SIDS.2 FGCB was defined as “A linear row of at least 8 ectopic granule cells (GCs) that is separated from the main DG in the supragranular (molecular layer, ML) or subgranular (hilus) sites. There is an acellular, eosinophilic zone of neuropil between the line of ectopic cells and the main DG. The linear row may be one or more cells thick. There may be pyknotic nuclei in the subgranular zone, which may represent apoptosis.”2