Glycine/serine ratio and the prenatal diagnosis of non-ketotic hyperglycinaemia.

We describe our experience of prenatal diagnosis of non-ketotic hyperglycinaemia in four at-risk pregnancies using the glycine/serine ratio in amniotic fluid obtained between 18 and 20 weeks of gestation. All glycine levels were in the normal range. Serine levels were normal in two patients and borderline in the others. Glycine/serine ratios were normal in two patients, moderately increased in one patient (+3 SD), and highly increased in one patient (+8 SD). All the children were perfectly normal at birth. Because of this false-positive prediction and the false-negative prediction recently reported, we suggest that this unreliable method should not be used.