GRN and frontotemporal dementia: Interestingly, an earlier study reported that FOXP2+, CTIP2+, or TBR1-TUJ1+ neuronal clusters are underrepresented in iPSC-derived cortical neurons obtained from FTD-GRN patients carrying heterozygous GRN IVS1 + 5G > C mutation [136] (Table 1).