Intracerebral blood and MRS in neonatal nonketotic hyperglycinemia

Abstract

Nonketotic hyperglycinemia is an inborn error of glycine metabolism leading to the accumulation of glycine in the brain. The neonatal form presents in the first days after birth with encephalopathy, seizures. and characteristic "hiccups." Rapid progression can lead to intractable seizures, coma, and respiratory failure. The outcome is invariably poor, and many die before age 1 year. The diagnosis of nonketotic hyperglycinemia is traditionally based on the finding of a raised cerebrospinal fluid-to-plasma-glycine ratio. An elevated glycine peak, using long echo time proton magnetic resonance spectroscopy, is also specific to nonketotic hyperglycinemia. The presence of blood in a cerebrospinal fluid sample is known to render the glycine level uninterpretable. However, there have been no reports of intracerebral blood confounding the cerebral glycine detected on long echo time proton magnetic resonance spectroscopy. We report on an infant who presented with neonatal encephalopathy and imaging findings consistent with hypoxic-ischemic encephalopathy, as well as intracerebral hemorrhage and an abnormal glycine peak on spectroscopy. The source of the abnormal glycine on long echo time proton magnetic resonance spectroscopy was intracerebral blood, highlighting an important confounder in the interpretation of long echo time proton magnetic resonance spectroscopy in suspected nonketotic hyperglycinemia.