Symptoms are likely due to increased GABA levels, detected in plasma, CSF, and basal ganglia.39 Although no contributed role of potentially altered glutamate levels to the phenotype has been described, a disturbed GABA‐glutamate ratio is postulated to contribute to this metabolic disorder.40, 41 Mutations in the GAD1 gene, encoding glutamate decarboxylase which irreversibly decarboxylates glutamate into GABA, have been described in one family with inherited spastic quadriplegic cerebral palsy type 1, seizures and developmental delay.42 This evidence concerns the gene GAD1 and Global developmental delay.