IGFBP2 and microcephaly: Because IGFBP2 and ID4 maintain NSCs as well as regulate cerebral and cognitive development [44–46, 60], IGFBP2 and ID4 dysregulation during NGLY1-defective cortical development could limit proliferation and cause premature differentiation in NSCs, which may underlie microcephaly in NGLY1-deficiency patients.