Practical difficulties in the diagnosis of transient non-ketotic hyperglycinaemia.

Making a diagnosis of transient non-ketotic hyperglycinaemia (tNKH) can be difficult. We report an infant who presented in the neonatal period with symptoms of NKH. Metabolic studies performed on day 2 of life showed raised cerebrospinal fluid (CSF) and plasma glycine, and a CSF:plasma glycine ratio consistent with NKH; however, a liver biopsy performed on day 5 revealed normal liver glycine cleavage system activity. Subsequently, the child's clinical condition improved in the absence of any therapeutic medication. Clinical assessment and developmental follow-up at 5 months, 1 year, and 2 years were age-appropriate. Guidance for the investigation and management of future suspected cases of tNKH is discussed.