Transient nonketotic hyperglycinemia in an asphyxiated patient with pyridoxine-dependent seizures

Epileptic encephalopathy with suppression-bursts and nonketotic hyperglycinemia

Bursts of paroxysmal activity alternating with lack of activity define the suppression-burst (SB) pattern that may be acute, in hypoxic-ischemic encephalopathy and barbiturate intoxication, or chronic in the course of early epileptic and neonatal myoclonic (NME) encephalopathies. Malformations, namely Aicardi syndrome and hemimegalencephaly, gene mutations - of ARX and MUNC18 -, and inborn errors of metabolism, namely glycine encephalopathy, are the main causes, with spasms indicating more likely a malformation whereas myoclonus indicates metabolic disorders. Although glycine encephalopathy has a very severe outcome in its classical expression, it may be transient in the neonatal period, for reasons yet not identified. Although glycine encephalopathy is the main identified cause of NME, the disorder may not cause SB, especially in cases with later onset. The biochemical bases, due to changes in one of the four proteins that compose the enzyme, are well understood, but there is no phenotype-genotype correlation. Prenatal diagnosis is based on villous biopsy. The mechanism of SB partly depends on glutamate - or glycine, the co-neurotransmitter for NMDA transmission - overflow, mainly in the immature brain but also in cases due to barbiturate intoxication. Energy supply defect may also be involved in some inborn errors of metabolism.

Pitfalls in measuring cerebrospinal fluid glycine levels in infants with encephalopathy

In encephalopathic infants, cerebrospinal fluid hyperglycinemia and elevated cerebrospinal fluid to plasma glycine ratio are considered pathognomonic of nonketotic hyperglycinemia. To evaluate the significance of cerebrospinal fluid hyperglycinemia and elevated cerebrospinal fluid to plasma glycine ratio in acutely encephalopathic infants, a retrospective chart review of all cases of isolated elevation of cerebrospinal fluid glycine levels at Arkansas Children's Hospital from January 1995 to December 2000 was performed. Twenty-two patients (14 males) were included. The most common diagnosis was hypoxic ischemic encephalopathy (n = 8). Nine patients had elevated cerebrospinal fluid to plasma glycine ratio, which was transient in 7 patients. This study shows that elevated cerebrospinal fluid to plasma glycine ratio can be encountered in a variety of clinical conditions. The significance of this observation in light of the poor prognosis of nonketotic hyperglycinemia and the possible role of glycine in the mechanism of ischemic neuronal injury is addressed.

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.

Clinical variability in glycine encephalopathy

Glycine encephalopathy (GCE) is an autosomal recessive error of glycine degradation, resulting in a poor outcome with severe mental retardation, intractable seizures and spasticity. Milder variants with a significantly better outcome have been reported, but an early prediction of the long-term outcome is not yet possible. With regard to the long-term outcome, the data reported in the literature of children with different GCE forms were compared. Determination of cerebrospinal fluid and plasma glycine concentrations at the time of diagnosis were not useful in differentiating mild and severe outcomes. By contrast, several clinical parameters correlate with a poor outcome: spastic quadriparesis, truncal hypotonia, typical electroencephalography patterns, congenital and cerebral malformations (e.g., corpus callosum hypoplasia). Hyperactivity, behavioral problems and choreiform movement disorders are associated with a milder outcome. Thus, prediction of the outcome of GCE may be facilitated by searching for selected clinical parameters. In addition, early neuroimaging may be a valuable tool in predicting the outcome of GCE.

Glycine facilitates transmitter release at developing synapses: a patch clamp study from Purkinje neurons of the newborn rat

Synaptic currents in immature Purkinje cells from rats on postnatal days 0-14 (P0-P14) were studied using whole-cell patch-electrodes applied to cerebellar slices (200 micro m in thickness). Purkinje cells (held at -40 mV) showed excitatory postsynaptic currents (EPSCs) and inhibitory postsynaptic currents (IPSCs) spontaneously. From P2 to P12 the frequencies of miniature EPSCs and miniature IPSCs in the Purkinje cells increased by 10-fold or more, suggesting progressive formation of functional synapses during this period. Application of glycine (100 micro M) to an immature Purkinje cell at P3-10 immediately increased the frequencies of both EPSCs and IPSCs. The effects of glycine showed maximum at P5-6 for EPSCs and at P9-10 for IPSCs and decreased thereafter. Facilitatory effects of glycine were suppressed by strychnine (1 micro M), a specific blocker of the ionotropic glycine receptor, while the effects were also induced by other glycinergic agonists, including alpha-L-alanine (1 mM), L-serine (1 mM) and taurine (500 micro M). The site of glycinergic effects was studied by removing the action potential generation in cerebellar slices. Following the addition of tetrodotoxin (TTX, 1 micro M), the glycine-induced facilitation of EPSC almost disappeared, while that of IPSC remained (i.e. miniature IPSCs) and reached more than half of the value without TTX. These findings suggest that the ionotropic glycinergic receptors are expressed transiently but profoundly in the developing cerebellum, and that the distributions of these receptors causing excitation are different at excitatory and inhibitory presynaptic neurons. The glycine receptors may play distinct roles in the maturation and organization of cerebellar neural circuits.

Transient nonketotic hyperglycinemia: two case reports and literature review

Transient nonketotic hyperglycinemia is characterized by clinical and biochemical findings similar to those seen in classic nonketotic hyperglycinemia. Abnormalities in amino acids are partially or completely resolved in a period ranging from days to months. Almost all patients with the classic form of nonketotic hyperglycinemia survive with severe neurologic sequela, whereas most of the patients with the transient form exhibit normal development. Therefore, distinguishing the transient form of nonketotic hyperglycinemia from classic nonketotic hyperglycinemia is important to predict outcome of the patients. Transient nonketotic hyperglycinemia has been reported in only seven neonates. This article adds two cases to the transient nonketotic hyperglycinemia and reviews the relevant literature. Common clinical features were determined, and presence of miotic pupils was stressed.

Heterozygous GLDC and GCSH gene mutations in transient neonatal hyperglycinemia

Transient neonatal hyperglycinemia is clinically or biochemically indistinguishable from nonketotic hyperglycinemia at onset. In the case of transient neonatal hyperglycinemia, the elevated plasma and cerebrospinal fluid glycine levels are normalized within 2 to 8 weeks. To elucidate the pathogenesis of transient neonatal hyperglycinemia, we studied three patients by screening mutations in the genes that encode three components of the glycine cleavage system. Heterozygous mutations were identified in all of the three patients, suggesting that transient neonatal hyperglycinemia develops in some heterozygous carriers for nonketotic hyperglycinemia.