Glutaminase deficiency has recently been identified as a novel inherited metabolic disorder with a broad phenotypic spectrum ranging from early-onset global developmental delay to lethal early neonatal encephalopathy. We describe three infants from two unrelated families who presented clinically with neonatal onset refractory burst-suppression epileptic encephalopathy and respiratory failure, progressing to either a persistent vegetative state or early death. One patient remains alive at the age of six years. Metabolic investigations demonstrated elevated glutamine concentrations in cerebrospinal fluid and increased serum alanine and glutamine levels, biochemical features characteristic of urea cycle disorders, while ammonia levels remained within the normal range. Notably, brain magnetic resonance imaging revealed cystic lesions resembling the neuroimaging findings typically observed in patients with urea cycle defects. Exome sequencing identified a homozygous, unreported missense variant in GLS (NM_014905.5:c.1174G > A; p.Gly392Arg) in both siblings from family 1, and a novel homozygous missense variant (NM_014905.5:c.1031 T > C; p.Leu344Pro) in the proband from family 2. Functional studies of patient fibroblasts and recombinantly expressed mutant glutaminase protein, demonstrated a complete glutaminase deficiency. In addition, patient-derived fibroblasts exhibited pronounced ultrastructural abnormalities, including nuclear dysmorphisms, lysosomal dysfunction with glycogen accumulation, ER stress, Golgi disruption, and mitochondrial fragmentation, along with altered cellular bioenergetics characterized by impaired mitochondrial respiratory function. The biochemical and clinical findings in our patients support a key role for elevated glutamine in the neuropathogenesis of both glutaminase-deficient patients and individuals with hepatic encephalopathy and/or urea cycle defects.

Identifying neurometabolic disorders that lead to neonatal encephalopathy is difficult, and access to exome sequencing is a significant advantage in developing countries. We present a case of neonatal encephalopathy characterized by refractory seizures and significant apnea resulting from glutaminase deficiency, along with elevated levels of glutamine and glycine in the cerebrospinal fluid. Although the condition was fatal, it was possible to offer genetic counseling and recommendations for future pregnancies following exome sequencing.

The identification and understanding of the monogenic causes of neurodevelopmental disorders are of high importance for personalized treatment and genetic counseling. To identify and characterize novel genes for a specific neurodevelopmental disorder characterized by refractory seizures, respiratory failure, brain abnormalities, and death in the neonatal period; describe the outcome of glutaminase deficiency in humans; and understand the underlying pathological mechanisms. We performed exome sequencing of cases of neurodevelopmental disorders without a clear genetic diagnosis, followed by genetic and bioinformatic evaluation of candidate variants and genes. Establishing pathogenicity of the variants was achieved by measuring metabolites in dried blood spots by a hydrophilic interaction liquid chromatography method coupled with tandem mass spectrometry. The participants are 2 families with a total of 4 children who each had lethal, therapy-refractory early neonatal seizures with status epilepticus and suppression bursts, respiratory insufficiency, simplified gyral structures, diffuse volume loss of the brain, and cerebral edema. Data analysis occurred from October 2017 to June 2018. Early neonatal epileptic encephalopathy with glutaminase deficiency and lethal outcome. A total of 4 infants from 2 unrelated families, each of whom died less than 40 days after birth, were included. We identified a homozygous frameshift variant p.(Asp232Glufs*2) in GLS in the first family, as well as compound heterozygous variants p.(Gln81*) and p.(Arg272Lys) in GLS in the second family. The GLS gene encodes glutaminase (Enzyme Commission 3.5.1.2), which plays a major role in the conversion of glutamine into glutamate, the main excitatory neurotransmitter of the central nervous system. All 3 variants probably lead to a loss of function and thus glutaminase deficiency. Indeed, glutamine was increased in affected children (available z scores, 3.2 and 11.7). We theorize that the potential reduction of glutamate and the excess of glutamine were a probable cause of the described physiological and structural abnormalities of the central nervous system. We identified a novel autosomal recessive neurometabolic disorder of loss of function of glutaminase that leads to lethal early neonatal encephalopathy. This inborn error of metabolism underlines the importance of GLS for appropriate glutamine homeostasis and respiratory regulation, signal transduction, and survival.