Glycine encephalopathy
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Sometimes referred to as GCE, Non-Ketotic Hyperglycinemia, Nonketotic Hyperglycinemia, NKH
Classic Neonatal Form or Classic Form: Most patients with GCE have the neonatal phenotype, presenting in the first few days of life with lethargy, hypotonia, and myoclonic jerks,and progressing to apnea, and often to death. Those who regain spontaneous respiration develop intractable seizures and profound mental retardation.
Infantile Form: Patients present with seizures and have various degrees of mental retardation after a symptom-free interval and seemingly normal development for up to 6 months.
Mild-episodic form: Patients present in childhood with mild mental retardation and episodes of delirium, chorea, and vertical gaze palsy during febrile illness.
Late-onset form: Patients present in childhood with progressive spastic diplegia and optic atrophy, but intellectual function is preserved and seizures have not been reported
Atypical Form: Unlike the classic neonatal form of the disorder, atypical or mild glycine encephalopathy is phenotypically heterogeneous and nonspecific, making diagnosis difficult. The occurrence of an expressive speech deficit and neurologic abnormalities during intercurrent infections as striking features of the milder form of the disease.
Transient Form: Transient neonatal hyperglycinemia (TNH) is characterized by elevated plasma and CSF glycine levels at birth that are normalized within 2 to 8 weeks. TNH is clinically and biochemically indistinguishable from typical nonketotic hyperglycinemia at onset.
Nonketotic hyperglycinemia or Glycine Encephalopathy is inherited as an autosomal recessive trait.
