Introduction: We report on the MRI brain findings on two new cases of serine deficiency due to phosphoserine aminotransferase (PSAT1) deficiency, presenting with congenital microcephaly (<3rd centile at birth) and intrauterine growth retardation who later developed encephalopathy and spasticity.

Methods: Case Report

Results: The diagnosis was confirmed by serine levels in plasma and CSF that were low relative to the reference population and Whole Exome Sequence (WES).: MRI findings during the neonatal period were similar in both cases: 1. Diffuse cortical volume loss with prominent subarachnoid spaces and prominent ventricles 2. Malrotation of the hippocampi 3. Asymmetric subcortical white matter hyperintensities, most predominantly in the temporal lobes. MRI at 2 years of age in case 2 showed 1. Diffuse white matter volume loss with findings similar to PVL 2. Delayed myelination 3. Corpus callosal hypoplasia with absent splenium 4. Brachycephaly 5. Unfolding of the hippocampi. One case previously reported who died at 7 months of age revealed generalized atrophy and a hypoplastic cerebellar vermis.

Conclusion: The Brain MRI most consistent findings of Phosphoserine aminotransferase deficiency in untreated patients in these two patients were: Diffuse cortical volume loss, Malrotation of the hippocampi, Asymmetric subcortical white matter hyperintensities, most predominantly in the temporal lobe and delayed myelination.  These constellation findings have not previously been reported to the best of our knowledge.