GPM6A and dentin dysplasia: Regarding the 4q duplication phenotypes, Thapa et al. proposed 4q33–q34 to be a critical region and suggested that dosage sensitivity of one or both of GLRA3 (MIM# 600421) and GPM6A (MIM# 601275) may be associated with DD and ID, while HAND2 may be critical for craniofacial development [9].