Nonketotic hyperglycinemia: electroencephalographic and evoked potential abnormalities

Area of Science:

• Neurology
• Clinical Neurophysiology
• Biochemistry

Background:

• Nonketotic hyperglycinemia (NKH) is a rare inborn error of metabolism.
• It is characterized by glycine accumulation in body fluids.
• Neurological manifestations are severe, including intractable seizures and developmental delay.

Purpose of the Study:

• To investigate the electrophysiological findings in patients with nonketotic hyperglycinemia.
• To characterize the evolution of EEG patterns and evoked potentials in NKH.

Main Methods:

• Serial electroencephalography (EEG) recordings were performed on five patients with NKH.
• Evoked-response studies, including brainstem auditory evoked responses (BAERs) and visual evoked responses (VERs), were conducted.

Main Results:

• All patients exhibited grossly abnormal EEGs.
• Neonatal EEGs showed suppression-burst patterns, evolving to hypsarrhythmia in infancy.
• Later EEGs revealed multifocal epileptiform discharges and hypsarrhythmia during sleep.
• Abnormal BAERs (prolonged I-V interval) were observed in four patients.
• Abnormal VERs were noted in two patients.

Conclusions:

• EEG patterns in NKH evolve significantly with age, reflecting disease progression.
• Evoked response abnormalities suggest widespread central nervous system dysfunction in NKH.
• Electrophysiological studies are crucial for monitoring disease course and severity in nonketotic hyperglycinemia.