Natural history and outcome of nonketotic hyperglycinemia in China

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.

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.

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.

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.