Nonketotic hyperglycinemia: a cause of encephalopathy in children

Nonketotic hyperglycinemia is a rare metabolic disorder with severe, frequently fatal, neurologic manifestations. Reliable and accurate diagnosis depends on careful interpretation of laboratory findings. The clinical suspicion should lead to determination of glycine in plasma and cerebrospinal fluid. Amino acid analysis presents diagnostic values for classic nonketotic hyperglycinemia, but it also should be performed in suspected cases of atypical nonketotic hyperglycinemia and in children with seizures, failure to thrive, behavior problems, and uncoordinated movements. Clinical assessment should be reinforced by demonstration of elevated cerebrospinal fluid-to-plasma glycine ratio. Confirmatory diagnosis requires enzymatic and genetic investigation of glycine cleavage system. An early diagnosis, though not affecting clinical outcome, allows proper genetic counseling, with the possibility of prenatal diagnosis. We report 3 cases of nonketotic hyperglycinemia, 2 typical neonatal and 1 atypical, diagnosed in Pediatric Hospital of Coimbra, Portugal, and investigated at Laboratory of Biochemical Genetics in 2004 to 2010 (incidence 1:47 455; prevalence 1:782 951).