[Clinical and genetic analyses of a family with atypical nonketotic hyperglycinemia caused by compound heterozygous mutations in the GLDC gene]

Natural history and outcome of nonketotic hyperglycinemia in China

Introduction

Nonketotic hyperglycinemia (NKH) is a rare, life-threatening genetic disorder. The patients usually show heterogeneous and nonspecific symptoms, resulting in diagnosis challenges using conventional approaches. Here, the clinical presentation and genetic features of 20 Chinese patients were examined and reported in order to clarify the natural history and prognosis of NKH in China.

Methods

The Human Gene Mutation Database and literature regarding NKH in China were reviewed. Age of onset, clinical characteristics, genetic analysis, cranial magnetic resonance imaging (MRI) and electroencephalography (EEG) examinations, and outcome of the patients were analyzed. Natural history experiences and follow-up assays for five patients who were followed in our center were described.

Results

Among all 20 NKH patients, 17 (85%) had the neonatal type and 3 (15%) had the infantile type, no late-onset cases were detected. Patients showed up for admission with a history of seizures (15/20), lethargy (14/20), hypotonia (11/20), apnea (9/20), and feeble sobbing (4/20). Brain MRI findings included abnormal signals in the internal capsule, cerebellum, or brainstem (6/14), dysplasia of the corpus callosum (5/14), and white matter abnormalities (3/14). EEG evaluations showed anomalies such as burst suppression (4/8) and hypsarrhythmia and/or epileptic activity (6/8). Median values of cerebrospinal fluid (CSF) glycine levels, plasma glycine levels and CSF/plasma glycine ratios were135.2 (range, 6.3-546.3) μmol/L, 998.2 (range,75-3,084) μmol/L, 0.16 (range, 0.03-0.60) respectively. Genetic analyses revealed four new variations and GLDC, AMT gene abnormalities in 13 (65%), 7 (35%) case, respectively. Prognosis information was available for 18 cases: nine patients died, eight in the neonatal period. Among the nine survivors, varying developmental disorders were observed.

Discussion

Different disease processes and outcomes were found in Chinese NKH patients, according to this study. The initial clinical presentations, CSF glycine levels and CSF to plasma glycine ratios do not reliably predict prognosis, while MRI and EEG abnormalities may indicate a poor outlook. NKH diagnosis should be considered for neonates presenting specific symptoms. The present survey provides clinical data that support the development of a standardized protocol for diagnosing and treating NKH in China.

Novel GLDC Compound Heterozygous Variant Leading to Nonketotic Hyperglycinemia: Case Report and Literature Review

Nonketotic hyperglycinemia (NKH) is a lethal autosomal recessive disease resulting from alterations in glycine metabolism, commonly caused by mutations in glycine decarboxylase (GLDC). The symptoms of NKH usually manifest in the neonatal period, and can be categorized into severe NKH and attenuated NKH based on the clinical outcome. To date, only a few NKH cases have been reported in China. We here report a case of a neonate with severe NKH carrying a novel compound heterozygous variant in GLDC. The patient was a 68-h-old girl who had progressive lethargy, no crying, and poor sucking ability from birth, and was therefore transferred to our department. On admission, the patient was supported by intubation and ventilation and presented with profound coma. Metabolic investigation indicated a markedly increased glycine concentration both in the plasma and cerebrospinal fluid (CSF). Symptomatic treatments were administered, but the patient's condition did not improve substantially. Whole-exome sequencing identified compound heterozygous mutations (c.1261G>C, p.G421R and c.450 C>G, p.N150K) in GLDC, which were inherited from the mother and the father, respectively. The patient was hospitalized for 8 days in our department and died 2 days after discharge. We further summarize the clinical features, genetic characteristics, administered treatment, and prognosis of previously reported Chinese NKH patients for context. Our results highlight that due to the non-specific clinical phenotypes of NKH and difficulty in obtaining CSF samples, genetic testing is a crucial tool, not only for a diagnosis but also for predicting the clinical outcome and can potentially help to determine the optimal therapeutic strategy.