A hypothalamic digoxin-mediated model for autism.
The isoprenoid pathway and its metabolites--digoxin, dolichol, and ubiquinone--were assessed in autism. The isoprenoid pathway and digoxin status was also studied for comparison in individuals of differing hemispheric dominance to determine the role of cerebral dominance in the genesis of autism. There was an upregulation of the isoprenoid pathway as evidenced by elevated HMG CoA reductase activity in autism. Digoxin, an endogenous Na+-K+ ATPase inhibitor secreted by the hypothalamus, was found to be elevated and RBC membrane Na+-K+ ATPase activity was found to be reduced in autism. Membrane Na+-K+ ATPase inhibition can result in increased intracellular Ca2+ and reduced magnesium levels. Hypothalamic digoxin can modulate conscious and subliminal perception and its dysfunction may lead to autism. Digoxin can also preferentially upregulate tryptophan transport over tyrosine resulting in increased levels of depolarizing tryptophan catabolites--serotonin, quinolinic acid (NMDA agonist), strychnine (blocks glycinergic inhibitory transmission), and nicotine (promotes dopamine release) and decreased levels of hyperpolarizing tyrosine catabolites--dopamine, noradrenaline, and morphine--contributing to membrane Na+-K+ ATPase inhibition. Increased nicotine levels can produce increased dopaminergic transmission in the presence of low dopamine levels. NMDA excitotoxicity could result from hypomagnesemia induced by membrane Na+-K+ ATPase inhibition and quinolinic acid, an NMDA agonist acting on the NMDA receptor. Hypomagnesemia and increased dolichol level can affect glycoconjugate metabolism and membranogenesis leading on to disordered synaptic connectivity in the limbic allocortex and defective presentation of viral antigens and neuronal antigens contributing to autoimmunity and viral persistence important in the pathogenesis. Membrane Na+-K+ ATPase inhibition can produce immune activation, a component of autoimmunity. Mitochondrial dysfunction consequent to altered calcium/magnesium ratios and reduced ubiquinone levels can result in increased free radical generation and reduced free radical scavenging and defective apoptosis leading to abnormal synaptogenesis. Autism can thus be considered a syndrome of hypothalamic digoxin hypersecretion consequent to an upregulated isoprenoid pathway. The biochemical patterns including hyperdigoxinemia observed in autism correlated with those obtained in right hemispheric chemical dominance. Right hemispheric chemical dominance is a predisposing factor for autism.
Department of Neurology, Medical College Hospital, Trivandrum, Kerala, India.
Ravi Kumar
RK
Kurup
Parameswara Achutha
PA
Kurup
D000293:Adolescent; D001321:Autistic Disorder / Q000378:metabolism*; D002648:Child; D004077:Digoxin / Q000097:blood*; D004286:Dolichols / Q000097:blood; D005260:Female; D006801:Humans; D007031:Hypothalamus / Q000201:enzymology / Q000378:metabolism*; D008274:Magnesium / Q000097:blood; D008297:Male; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D014451:Ubiquinone / Q000097:blood
D004286:Dolichols; D014451:Ubiquinone; D014443:Tyrosine; D004077:Digoxin; D014364:Tryptophan; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium