GLS and hyperinsulinemic hypoglycemia, familial, 4: Global Developmental Delay, Progressive Ataxia, And Elevated Glutamine (GDPAG; OMIM# 618412; aka Glutaminase Deficiency, GLSD) is a severe neurological disorder resulting from mutations in the Glutaminase (GLS) gene, a gene encoding the enzyme required for conversion of glutamine to glutamate, a critical excitatory neurotransmitter in the brain.