Phosphoserine aminotransferase deficiency: imaging findings in a child with congenital microcephaly

Serine deficiency disorders can result from deficiency in one of three enzymes. Deficiency of the second enzyme, 3-phosphoserine aminotransferase (PSAT), has been reported in two siblings; the eldest investigated for acquired microcephaly, spasticity and epilepsy. Our patient had neurological symptoms at birth. Fetal magnetic resonance imaging (MRI) at 35-week gestation demonstrated microencephaly and gyral simplification (anterior > posterior) which was confirmed upon postnatal MRI. Congenital microcephaly was apparent at birth. PSAT deficiency was confirmed when exome sequencing identified biallelic mutations in PSAT1 and biochemical testing noted low plasma serine and cerebral spinal fluid serine. Despite oral serine and glycine supplementation at 4 months old, the patient showed little neurodevelopmental progress and developed epileptic spasms at 10 months old. PSAT deficiency should be considered for patients with congenital microcephaly. Although further characterization of MRI findings in other patients is required, microencephaly with simplified gyral pattern could provide imaging clues for this rare metabolic disorder.