ASNS and congenital microcephaly - severe encephalopathy - progressive cerebral atrophy syndrome: Asparagine synthetase deficiency (ASNSD) refers to a congenital metabolic abnormality caused by mutation in the asparagine synthetase (ASNS) gene encoded by chromosome 7q21.[1] Clinically, ASNSD is characterized by dysplasia of the central nervous system and can present as congenital microcephaly, severe psychomotor developmental retardation, excessive irritability, refractory epilepsy, spasticity, dyskinetic quadriplegia, difficulty in feeding, and insufficient ventilation.[2]