We report a case of preterm infant born with prenatal diagnosis of cystic hygroma in the neck and congenital heart defect. Physical exam showed a hypotonic infant with dysmorphic features. Noonan syndrome was diagnosed. This newborn presented with progressive encephalopathy leading to a workup for metabolic disorders. The findings of elevated glycine levels associated with ketosis prompted the diagnosis of propionic acidemia. This case demonstrates that metabolic disorders can co-exist with other genetic syndromes and a high index of suspicion is needed in order to make the diagnosis and determine available treatment options. Genetic counseling should be offered to the parents as these disorders may affect future.