Mutations in a number of identified genes have been found to underlie autosomal recessive primary microcephaly (MCPH) (e.g., MCPH1, ASPM, CASC5, and WDR62) and thanatophoric dysplasia (FGFR3), a subtype of megalencephaly (Jayaraman et al., 2018; Juric-Sekhar and Hevner, 2019). This evidence concerns the gene FGFR3 and autosomal recessive primary microcephaly.