Krein graduated from Rutgers University with a bachelor's degree in biology and a master's degree in neuroscience.[1][2][7] He obtained a doctoral degree in cell and development biology from the University of Medicine and Dentistry of New Jersey's Robert Wood Johnson Medical School in 1996.[1][4][8] He graduated from medical school at Thomas Jefferson University in 2000.[1][4] He completed an internship in emergency medicine and general surgery and a residency in otolaryngology at Jefferson.[6] He completed a fellowship in facial plastic and reconstructive surgery at the Medical College of Virginia.[6][9]