Mild variant of nonketotic hyperglycinemia with typical neonatal presentations: mutational and in vitro expression analyses in two patients.

In neonatal-onset nonketotic hyperglycinemia, severe psychomotor retardation is the expected uniform outcome. We report two patients with typical neonatal presentation who showed far better developmental outcomes. The in vitro expression analysis of the identified GLDC mutations revealed considerable residual enzyme activity, suggesting prognostic and enzymatic heterogeneity even in neonatal-onset nonketotic hyperglycinemia.