Brain MRI features in late-onset nonketotic hyperglycinemia.

A 22-year-old woman presented with learning disability and gait unsteadiness since adolescence. Medical history revealed episodes of encephalopathy and myoclonic jerks associated with intercurrent infections. Examination showed spastic paraparesis, ataxia and optic atrophy. Neuroimaging revealed agenesis of corpus callosum (Figure). Plasma amino acid analysis disclosed elevated glycine levels with an increased cerebrospinal fluid:plasma glycine ratio. Nonketotic hyperglycinemia (MIM #605899) is an autosomal recessive disorder of glycine metabolism caused by a defect in the glycine cleavage system with three different clinical forms: neonatal, infantile and late-onset with heterogeneous brain malformations, such as abnormal corpus callosum, gyral malformations and enlarged ventricles1,2.