Clinical criteria for the diagnosis of PEHO syndrome as described by Somer3
| Necessary criteria | Supportive criteria | Features that argue against the PEHO syndrome |
| Infantile, usually neonatal hypotonia | Subtle dysmorphic features with narrow forehead, epicanthic folds, short nose, open mouth, receding chin, tapering fingers | Microcephaly at birth |
| Convulsive disorder manifesting with myoclonic seizures and infantile spasms | Oedema of the face and limbs, especially in early childhood | Abnormal gyral formation in neuroradiological studies |
| Profound psychomotor retardation with severe hypotonia; absence of motor milestones and speech | Brisk tendon reflexes in early childhood | Predominating spasticity in infancy |
| Absence or early loss of visual fixation with atrophy of optic discs by 2 years; normal electroretinogram, extinguished visual evoked potentials | Abnormal brainstem auditory evoked potentials | Reappearance of visual contact after cessation of infantile spasms |
| Progressive brain atrophy in neuroimaging studies, particularly in the cerebellum and brainstem; milder supratentorial atrophy | Absent cortical responses of somatosensory evoked potentials | Hepato/splenomegaly or storage disorder in histological studies |
| Slow nerve conduction velocities in late childhood | ||
| Dysmyelination on MRI |
PEHO, progressive encephalopathy, hypsarrhythmia and optic atrophy.