This chapter provides a review of selected metabolic disorders resulting from genetic mutations and the diagnostic methods used to identify them prenatally or in the early neonatal period. Prenatal and neonatal diagnostic technologies have evolved gradually over four decades, but they are expanding and changing dramatically in the 21st century, as is their application in population-based screening and/or targeted assessment of at-risk couples. For instance, preimplantation genetic diagnosis has been a major advance. Emphasis herein has been placed on prototype Sachs that have stimulated seminal efforts to improve medical practices in these fields. Future developments in prenatal screening and diagnosis, along newborn screening expansion, seem likely to continue rapid translation to the bedside because of extraordinary biotechnological advances.