Hengel et al recently reported that bi-allelic loss-of-function mutations in UDP-Glucose 6-Dehydrogenase (UGDH) caused a severe epileptic encephalopathy syndrome-Jamuar syndrome (OMIM#618792). The functional studies partially recapitulated the clinical phenotypes in the patient-derived cerebral organoid. A reduced number of proliferating neuronal progenitors in cerebral organoids was shown, which is a critical mechanism in congenital microcephaly (CM) whose patients were born with an occipitofrontal circumference (OCF) more than 2 standard deviations below average for age and sex. However, none of the reported patients in the article presented the phenotype as CM.