Epileptic encephalopathies

Epileptic encephalopathies are a heterogenous group of conditions where the epileptic activity itself contributes to severe cognitive and behavioral impairments above and beyond what might be expected from the underlying pathology alone (e.g., cortical malformation), and that these can worsen over time”^[1]. According to the ILAE commission (2017)^[2] “in an epileptic encephalopathy, the abundant epileptiform activity interferes with development resulting in cognitive slowing and often regression, and sometimes is associated with psychiatric and behavioural consequences” and that the encephalopathic impact of the epileptiform activity could cause regression in patients with both normal development and pre-existing developmental delay, who then show developmental plateauing or regression. The disorders are usually refractory to standard antiepileptic drugs (AEDs).

The report of the International League Against Epilepsy (ILAE) Task Force on classification and terminology includes 8 syndromes under epileptic encephalopathies:

• Early Myoclonic Encephalopathy
• Early Infantile Epileptic Encephalopathy (Ohtahara syndrome)
• Epilepsy of infancy with migrating focal seizures
• West Syndrome
• Dravet syndrome
• Epilepsy with Myoclonic Astatic Seizures
• Lennox-Gastaut syndrome
• Epilepsy with Continuous Spike-Waves during Slow Wave Sleep including Landau-Kleffner syndrome and Atypical benign partial epilepsy.

One approach to epileptic encephalopathies is based on whether the presentation is with seizures as a prominent/unique symptom or where they are associated with movement disorders, dysmorphic features or multi-organ involvement.

• Vitamin or enzymatic cofactor dependency
  • Pyridoxine dependent epilepsy
  • Folinic acid responsive epilepsy
  • Pyridoxal-5′-phosphate responsive epilepsy
• Channelopathy
  • Dravet and Dravet-like syndrome
• Unknown/multiple etiology
  • Ohtahara syndrome (EIEE)
  • Early myoclonic encaphalopathy (EME)
• Single enzyme or protein dysfunction
  • Syntaxin binding Protein 1 (STXBP1) deficiency
  • Glutamate mitochondrial transporters deficiencies (SLC25A22 and SLC25A18)
  • Phospholipase C beta-1 deficiency
  • MAGI2 related epileptic encephalopathy
  • Protocadherin 19 related epileptic encephalopathy
• Disorders of amino acids metabolism
  • Hyperprolinemia type II
• Neurotransmitters disorders
  • GABA transaminase deficiency

• Chromosomal abnormalities
  • 1p36 monosomy
  • Wolf-Hirschhorn syndrome
  • 18q- syndrome
  • Angelman syndrome
  • Ring chromosome 20 syndrome
  • Down syndrome
• Single enzyme or protein dysfunction
  • Cyclin-dependent kinase-like 5 (CDKL5) deficiency
  • Rett Syndrome (MeCP2, CDKL5 or FOXG1-related)
• Cerebral malformations associated disorders
  • Focal cortical dysplasia (TSC1 and TSC2)
  • Polymicrogyria (SRPX2, KIAA1279, GPR56, PAX6, TBR2, COL18A1, RAB3GAP1, 22q11, FLN1A, ARFGEF2, LRP)
  • Subcortical band heterotopia (DCX, LIS1, trisomy 9p)
  • Periventricular nodular heterotopia (unbalanced translocation,t[1; 6][p12; p12.2)]
  • Lissencephaly (LIS1, DCX, microdeletion in 17p including LIS1 and YwaE, ARX, TUBA1A, RELN)
  • Schizencephaly (EMX2 involved in sporadic cases)
  • Early infantile epileptic encephalopathy type I (ARX-related EIEE1)
  • Miller-Dieker syndrome
  • Smith-Lemli–Opitz syndrome
• Disorders of amino acids metabolism
  • Phenylketonuria and hyperphenylalaninemias
• Vitamin or enzymatic cofactor dependency
  • Sulfite oxidase deficiency
  • Molybdenum cofactor deficiency
  • Menkes disease
• Purine and pyrimidine metabolism disorders
  • Adenilosuccinate lyase deficiency
  • Dihydropyriminidase and Dihydropyrimidine dehydrogenase deficiency

• Energetic failure
  • GLUT1 deficiency syndrome
  • Creatine deficiency syndromes (AGAT, GAMT and X-linked creatine transporter deficiency)
• Cerebral malformations associated disorders
  • EIEE1 (ARX-related epileptic encephalopathy)
• Neurotransmitters disorders
  • 4-hydroxybutyric aciduria (SSADH)

• Acute multiorgan involvement
  • Endogenous toxicity
    • Urea cycle disorders
    • Organic acidurias
    • Congenital disorders of glycosylation
    • Glutathione synthetase deficiency
    • Mitochondrial disorders (SUCLA2, SUCLG1)
  • Vitamin or enzymatic cofactor dependency
    • Biotin metabolism disorders
  • Neurotransmitters disorders
    • Congenital glutamine deficiency
  • Channelopathy
  • Developmental delay, Epilepsy and Neonatal Diabetes (DEND syndrome)
  • Single enzyme or protein dysfunction
    • Hyperinsulinism/Hyperammoniemia (HI/HA)
• Chronic multiorgan involvement
  • Energetic failure
    • Mitochondrial disorders (Leigh syndrome, multiple deletion syndrome or Alpers disease, pyruvate dehydrogenase deficiency)
  • Storage disorders
    • Lysosomal disorder (Krabbe disease)
    • Peroxisomal disorder (neonatal adrenoleukodystrophy, Zellweger syndrome, infantile Refsum disease, punctuate rhyzomelic chondrodysplasia)
    • Niemann-Pick disease type A and C
    • Neuronal ceroid lipofuscinosis
  • Single enzyme or protein dysfunction
    • MAGI2 deletion syndrome
  • Disorders of amino acids metabolism
    • Serine byosynthesis disorders
  • Unknown
    • Nesidioblastosis