Do toxins trigger autistic regression?

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Do toxins trigger autistic regression?

• McGinnis WR, Miller VM, Audya T and Edelson S.
• Neurotoxic brainstem impairment as proposed
  threshold event in autistic regression.
• CRC Press 2009

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Intriguing phenomenon of autistic regression

• Widely recognized
• Usually 18-24 months of age
• Relatively rapid days or weeks
• Earlier problems in some children
• Published incidence as high as 50

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ARI Database
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Features of regression

• Vocalization loss acquired words or babbling
  (29 / 9. Lord 2004)
• Loss of social function, in some cases
  unassociated with loss of vocalization (Goldberg
  2003)
• Gastrointestinal impairment (Madsen 2004
  Goldberg 2004)

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GI tract in regressed cohorts

• Radiographic fecal loading or megacolon (100.
  Torrente 2002)
• Reflux esophagitis (69. Horvath 1999)
• Enterocolitis (88. Wakefield 1998, 2002)

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Toxins are plausible triggers

• Parallel increase in autism and
• environmental toxicants (Lathe 2008)
• Autism rates correlate with
• 1. Presence of toxic landfills (Ming 2008)
• 2. Estimated environmental cadmium
• and mercury (Windham 2006)
• 3. Proximity to mercury point sources
• (Palmer 2009)

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Toxins as triggers

• Elevated dental concentrations of mercury (Adams
  2007)
• Autistic symptoms correlate with
  mercury-consistent porphyrins (Geier 2008)
• Case reports
• Geier temporal association with mercury
• by injection
• Bradstreet, et al on-off speech on DMSA

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The case of R.K.

• Progressive loss of speech over weeks post
  one-time placement of 9 amalgams at age 4.
• By age 6, had regained 200 words, but elevated
  blood Hg explicable only on basis of amalgams.
• Subsequent loss of all speech immediately after
  one-time removal of amalgams without precautions.
  

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Toxins as triggers

• Many neurotoxins are oxidative, and oxidative
  modification is increased in brain of autistic
  children (Evans 2008 Lopez-Hurtado 2008
  Sajdel-Sulkowska 2008)
• Gliosis and neuronal loss in autism is consistent
  with toxicant effects (Kern 2006)

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Circumventricular Organs (CVO)

• Area postrema (AP) Posterior
  pituitary
• Median eminence (ME) Subfornical Organ
• Organum vasculosum Pineal Gland
• Nucleus Tractus Solitarius (NTS)
• Portals for toxins no blood-brain barrier (BBB)
• In and around the brainstem

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CVO are preferentially sensitive to a broad class
of neurotoxins

• Cadmium
• Monosodium glutamate (MSG)
• Paraquat
• Inorganic mercury (including inorganic mercury
  from metabolic conversion of organic and
  elemental forms)

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Cadmium

• Injections accumulate only in brain outside BBB,
  including AP and pineal (Arvidson 1986)
• Lipid peroxidation (Mendez-Armenta 2003) blocked
  by antioxidants (Kim 2008)
• Inhibits complex II and III (Wang 2004)

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MSG

• Injections accumulate only in brain outside BBB,
  including AP (Karcsu 1985) and ME (Meister 1989
  Peruzzo 2000)
• Lipid peroxidation, persistent for long periods
  (Bawari 1995 Singh 2003)
• Excitotoxic. In autism, GAD much lower in brain
  (Fatemi 2002)

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Paraquat

• Injections accumulate only in areas outside the
  BBB, including AP and pineal (Naylor 1995)
• Increased TNF-a and superoxide production by
  microglia (Wu 2005)
• Inhibits complexes II and IV
• (Palmeira 1995)

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Inorganic mercury

• Worrisome levels in air, water, soil (McGinnis
  2001) and food (Dufault 2009)
• Pink Disease proves fractional systemic
  absorption in children (McGinnis 2001)
• Injections accumulate in AP and brainstem motor
  nuclei (Arvidson 1992)
• Persists in brain for years (Vahter 1994)
• Immune stimulation (Havarinasab 2007) and
  increased microglia (Geier 2007)

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Elemental mercury

• Amalgam removal decreased plasma and red-cell
  inorganic mercury levels by 73 (Halbach 2008)

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Daily oral organic (methyl) mercury in primates

• In 6 brain areas, inorganic mercury averaged x30
  at 6 mos., x60 at 18 mos.
• By far, highest inorganic mercury at pituitary,
  only CVO examined.
• If stop organic dosing at 6 mos, inorganic
  mercury doubles in pituitary at 12 months, but
  not in regions with BBB.
• (Vahter 1994)

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Brainstem

• The hard-drive control panel for messages
  between brain and body
• Rimland emphasized brainstem in 1964, but scant
  current neuropath interest
• Many findings in autism consistent with brainstem
  dysfunction

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Brainstem medulla, pons, midbrain and
diencephalon
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Brain phylogeny
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x2
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Brainstem abnormalities

• Smaller medulla and midbrain on MRI (Courchesne
  1997 Hashimoto 1993)
• Reduced gray matter on MRI (Jou 2008)
• Ectopic neurons and aberrant tracts (Bailey 1998)
• Swollen medullary, thalamic, hypothalamic axon
  terminals (Weidenheim 2001)
• Abnormalities of inferior and superior olives
  (Kemper 1993 Kulesza 2008)

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Brainstem abnormalities

• Auditory brainstem response (Klin 1993 Kwon
  2007)
• Centrencephalic EEG (Gilberg 1983)
• Heart rate, respiratory and vascular response
  (Bonvallet 1963 Althaus 2004)
• Post-rotatory response (Ornitz 1983)

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Suggest CVO impairment

• Pineal abnormal melatonin production (Nir
  1995 Kulman 2000 Tordjmann 2005)
• Median eminence / posterior pituitary abnormal
  oxytocin production (Modahl 1998 Green 2001)

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Hypothalamus and pineal in relation to thalamus
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Dorsal vagal complex (DVC)

• Area postrema (AP)
• Dorsal motor nucleus of vagus (DMV)
• Nucleus tractus solitarius (NTS)
• The DVC mediates autonomic function of
• cervical, thoracic and abdominal viscera.

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Portals for toxins
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Dorsal vagal complex (DVC)
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Dorsal vagal complex (DVC)
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Area postrema

• No BBB
• Highly vascular and very long residence time of
  blood in capillaries
• So-called emesis center
• Ablation increases consumption of water or
  concentrated salt water, food aversions, craving
  for carbohydrates and bland food
• Flavor aversion 2 Cd reversed by DMSA

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Nucleus tractus solitarius

• Lacks BBB on one side (Gross 1990)
• Viscerosensory and visceromotor parasympathetic
  and sympathetic efferent
• Mediates social behavior, arousal, mood, emotion,
  anxiety, seizure activity and pain via limbic and
  cortical projections (Marvel 2004 Nemeroff 2006)

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Secretin and NTS

• Highest binding of infused secretin at NTS
  secretin activates NTS neurons (Yang 2004)
• Several studies reported improvements in social
  behaviormay relate to NTS effect (Myers 2008)
• Parent reports of sudden potty-training
  consistent with NTS effect (Beck, et al.)

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Dorsal motor nucleus of the vagus (DMV)

• Visceromotor peristalsis, esophageal sphincter
  tone, heart rate, pharyngeal and laryngeal
  musculature
• Tensor palati to open eustachian tube
• Viscerosecretory digestion, floral balance

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Phonation

• Significantly autonomic, subconscious
• DMV visceromotor to all the intrinsic and
  extrinsic muscles of larynx and pharynx
• Vagal alteration results in altered pitch
  (Shaffer 2005)
• Vagal dysarthria should not be confused with
  classical motor apraxia of speech

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DVC is anti-inflammatory
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Suggest DVC impairment

• Excessive thirst (Terai 1999)
• Salt-craving and flavor-aversion (ARI)
• Otitis media (Konstantareas 1987 Rosenhall 1999)
• Abnormal heart rate, respiratory and vascular
  (Bonvallet 1963 Althaus 2004)
• Depressed cardiac parasympathetic and abnormal
  baroreflex (Ming 2005)

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Suggest DVC impairment

• Esophageal reflux in 67 of regressed cohort
  (Horvath 1999)
• Fecal loading or megacolon in 100 of regressed
  cohort (Torrente 2002)
• Enterocolitis in 88 of regressed cohort
  (Wakefield 1998)
• Paneths cells enlarged with granules (Horvath
  1999)

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Duodenal Paneths cells (Courtesy
of K. Horvath, Thomas Jefferson University)
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Suggest DVC impairment

• 20 aged 3-5 identify better by pointing of
  23,685 children who regressed after 1 year, 4,141
  had speech replaced by whisper for at least one
  week, and 679 whispered long-term (ARI parent
  survey)
• Effective use of speech-generating device
  (Thunberg 2007)
• Frank dysarthria reported in autistic subgroup
  (Weissman 2008)

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Primary DVC impairment

• Sufficient explanation for core features of
  autistic regression
• Loss of social skills
• Loss of vocalization
• Gastrointestinal disease
• Impairment of other CVO might be expected to
  contribute to these core losses and other
  abnormalities

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Anatomical consistency

• Observation social regression often precedes
  loss of vocalization (Goldberg 2003) and may be
  unaccompanied by loss of vocalization (Goldberg
  2003 Lord 2004)
• Explanation no BBB at superior aspect of NTS to
  impede toxin entry, but entry to DMV requires
  diffusion from AP or NTS

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Parkinsonian parallels to autism

• Environmental factors strongly suspected
• Inflammation may be causative factor (Whitton
  2007)
• Digestive symptoms frequent or dominant (Spellman
  1977), with disordered motility (Cersosimo 2008),
  lax GE sphincter and reflux in 61 (Bassotti
  1998)
• DMV is consistent first site of pathology

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Ramifying pathology of PD(Braak H., et al. Cell
Tissue Res 200431121-134)
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Ramifying pathology of PD
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Possible mechanisms for ramifying brain pathology
in autism

• De-afferentiation may disturb the
• development of higher brain structures
• (Tanguay 1982 Gessaga 1986 Geva 2008)
• OR
• Cumulative effects of toxins / oxidative stress
• OR
• Diffusion of inflammatory cytokines produced
• by CVO in response to toxicants

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Microglial activation

• Brainstem has highest microglial density
• Many toxic exposures are associated with release
  of excitatory cytokines associated with neuronal
  cell loss (Mangano 2009)
• TNF-a is an cytokine suspected to play a
  pathogenic role in PD (McCoy 2003), and may be
  significant in autism

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TNF-a

• Elevated in CSF of regressed cohort (Chez 2007)
  and cohort with 10/12 regressed (Zimmerman 2005)
• High CSF/blood ratios suggest elevation due to
  increased brain production (Chez 2007)
• AP and ME lack blood-CSF barrier as well as BBB
  (Broadwell 1983)

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Endotoxin (LPS) model

• LPS poorly transits BBB
• Systemic LPS induces immediate robust TNF-a only
  in CVO and adjacent structures, most intensely in
  AP and ME
• TNF-a expression in NTS at 1.5 hours, marked by
  18 hours
• TNF-a absent in DMV initially, but present at 18
  hours (Breder 1994)

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Inflammatory toxins

• Cadmium potently stimulates inflammatory
  cytokines, including TNF-a (Souza 2004)
• MSG increases TNF-a in brain which is unprotected
  by BBB, with resulting neuronal death
  (Chaparro-Huerta 2002)
• Paraquat increases LPS-stimulated TNF-a from
  monocytes x18 (Erroi 1992)
• Inorganic mercury accumulation in CVO associates
  with increased glia (Vahter 1994)

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Cytokine transmission via CSF

• A pattern of inflammatory cytokine diffusion
  along nerve bundles suggests a diffusion pathway
  along small channels outside myelinated axons
  (Agnati 1995)
• Experimentally, cytokines circulate from lateral
  ventricle via white matter nerve bundles of the
  corpus callosum, external capsule and striatum
  all the way to the amygdala (Vitkovic 2000)

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Carboxyethylpyrrole (CEP)
Evans TA, et al., Am J Biochemistry and
Biotechnology 20084(2)61-72.
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Predicted threshold effects

• Oxidative stressregardless of causewould lower
  neurophysiological threshold for regression
  resulting from toxic effects on CVO
• 1. Additive to oxidative neurotoxicity
• of CVO-preferential toxins
• 2. Cholinergicespecially muscarinic
• systems are particularly sensitive to
  
• oxidative stress

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Implications of site-specificity

• Regressive threshold may be reached by isolated
  or cumulative exposure to one compound, or
  additive/cumulative exposures to distinct
  compounds.
• Impaired development or function of CVO by
  gestational or first-year factors not modulated
  directly by BBB would lower the threshold for
  regression triggered by CVO-preferential toxins
  after BBB maturation.

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Possible gestational influences

• Vulnerable period for thalidomide as risk factor
  for autism (20-24 days) corresponds to the timing
  of formation of the medullary motor nuclei
  (Rodier 1997)
• Cord-blood levels of mercury correlate with
  decreased autonomic activation of heart rate and
  brainstem auditory evoked potentials (Grandjean
  2004)

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CVO studies

• Morphology
• Receptor density
• Oxidative modification
• Cytokine levels
• Toxin levels
• Vagus