AFP and familial nephrotic syndrome: Biallelic crumbs 2 (CRB2) mutations cause both isolated early-onset SRNS and a severe phenotype manifesting as congenital nephrotic syndrome, exhibiting renal microcysts complicated by marked cerebral ventriculomegaly, gray matter heterotopia, and elevated levels of maternal serum alpha-fetoprotein and amniotic fluid alpha-fetoprotein [25–27].