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The Role of Heavy Metals and Environmental Toxins in Psychiatric Disorders

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James Greenblatt, MD

Every day we are exposed to toxins from our environment. We may ingest lead and copper from drinking water, phosphate from processed food and soda, various synthetic chemicals from plastic food containers, and pesticides from fruits and vegetables. Both natural heavy metals and man-made chemicals disrupt hormones and brain development. The brain, especially the developing brain, is very vulnerable to contaminants because of its large size (relative to total body weight) and its high concentration of fats which serve as a reservoir for toxicants to build up. This article will explain the role that heavy metals and environmental toxins play in ADHD.

In January 2016, President Obama declared a state of emergency in Flint, Michigan where thousands of residents were exposed to high levels of lead in their drinking water. The corrosive water from the Flint River caused lead from old water pipes to leach into the water supply, putting up to 12,000 children at risk of consuming dangerous levels of lead. Lead poisoning can cause irreversible brain damage and even death, and growing children are especially susceptible to its poisonous effects. Even low blood lead levels reduce IQ, the ability to pay attention, motor function, and academic achievement.

Blood lead levels in children have plummeted since the US phased out the use of leaded gas and paint in the 1970’s. Still, 24 million homes in the US contain deteriorated lead paint and elevated levels of lead-contaminated dust. Soil contains lead from air that settled during our previous industrial use. Old toys and toys from China may contain lead-based paint as well. Again, children are especially at risk of lead poisoning in these environments because they are likely to put their contaminated toys or hands in their mouth.

Since lead poisoning causes cognitive, motor, and behavioral changes, it is not surprising that it also causes ADHD. Lead exposure is estimated to account for 290,000 excess cases of ADHD in US children (Braun et al., 2006). A study on 270 mother-child pairs in Belgium found that doubling prenatal lead exposure (measured in cord blood) was associated with a more than three times higher risk for hyperactivity in boys and girls at age 7-8 (Sioen et al., 2013). A larger study on almost 5,000 US children aged 4-15 found children with the highest blood lead levels were over four times as likely to have ADHD as children with the lowest blood lead levels (Braun et al., 2006).

MRI scans from participants of the Cincinnati Lead Study had striking results: childhood lead exposure was associated with brain volume loss in adulthood. Individuals with higher blood lead levels as children had less gray matter in some brain areas. The main brain region affected was the prefrontal cortex which is responsible for executive function, behavioral regulation, and fine motor control (Cecil et al., 2008).

The CDC has set a blood lead level of 5 µg/dL as the reference value to identify children who require case management. However, many studies have shown lead levels <5 μg/dL still pose problems. For instance, researchers assessing 256 children aged 8-10 concluded, “even low blood lead levels (<5 μg/dL) are associated with inattentive and hyperactivity symptoms and learning difficulties in school-aged children” (Kim et al., 2010).

Copper is an essential trace mineral we must consume from our food supply. It is found in oysters and other shellfish, whole grains, beans, nuts, and potatoes. Like lead, copper can leach into the water supply when copper pipes corrode. One of copper’s roles in the body is to help produce dopamine, the neurotransmitter that provides alertness. However, too much copper creates an excess of dopamine leading to an excess of the neurotransmitter norepinephrine. High levels of these neurotransmitters lead to symptoms similar to ADHD symptoms: hyperactivity, impulsivity, agitation, irritability, and aggressiveness. In children with excess copper, stimulant medications don’t work as well and tend to cause side effects (agitation, anxiousness, change in sleep and appetite). Most ADHD medications work by increasing levels of dopamine, intensifying the effects of excess copper. In addition, excess copper blocks the production of serotonin, a mood-balancing neurotransmitter. This triggers emotional, mental, and behavioral problems, from depression and anxiety to paranoia and psychosis.

The neurotoxic effects of excess copper are well known and a few studies have assessed copper’s role in ADHD symptoms. When researchers compared copper levels in 58 ADHD children to levels in 50 control children, they observed that copper levels were higher in ADHD children. ADHD children also had a higher copper-to-zinc ratio that positively correlated with teacher-rated inattention (Viktorinova et al., 2016). Researchers in Belgium measured the heavy metal exposure of 600 adolescents aged 13-17. They found that an increase in blood copper was associated with a decrease in sustained attention and a decrease in short-term memory. This held true even though this population had normal copper levels (Kicinski et al., 2015). In a randomized controlled trial on 80 adults with ADHD, lower baseline copper levels were associated with better response to treatment with a vitamin-mineral supplement. Among those in the highest copper tertile, only 35% were responders compared to 77% in the middle copper tertile (Rucklidge et al., 2014).

Phosphate is a charged particle (an electrolyte) that contains phosphorus. Phosphorus is the second most abundant mineral in the body (the first is calcium). Phosphorus is a building block for bones and about 85% of total body phosphorus is found in the bones. Deficiencies are rare because phosphorus is naturally abundant in protein-rich foods like meat, poultry, fish, eggs, milk, and milk products as well as in nuts, legumes, cereals, and grains. Although phosphorus is an essential nutrient, too much can be problematic. The phosphate content of processed foods is much higher than that of natural foods, because phosphates are commonly used as additives and preservatives in food production. Our daily intake of phosphate food additives has more than doubled since the 1990’s (Ritz et al., 2012). Phosphorus, especially the form found in processed meats, canned fish, baked goods, and soda is quickly absorbed into the bloodstream so levels can rise rapidly.

Phosphorus reduces the absorption of other vital nutrients, many of which ADHD children are deficient in to begin with. For instance, too much phosphorus can lower calcium levels. High phosphorus coupled with low calcium intake leads to poor bone health. The typical American diet contains two to four times more phosphorus than calcium and soda is often a major contributor to this imbalance. In the body, phosphorus and magnesium bind together, making both minerals unavailable for absorption. This is most apparent when magnesium consumption is low and intake of phosphorus is high. Researchers have found that adding Pepsi to men’s diet for two consecutive days causes their blood phosphate levels to increase and their magnesium excretion to decrease (Weiss et al., 1992).

In the 1990’s, German pharmacist Hertha Hafer discovered that excess dietary phosphate triggered her son’s ADHD symptoms. Within her book, The Hidden Drug, Dietary Phosphate: Cause of Behavior Problems, Learning Difficulties and Juvenile Delinquency, she presents a low phosphate diet as a treatment for ADHD. A low phosphate diet led to dramatic improvements in her son’s behavior, well-being, and school performance, rendering medication unnecessary. Her family’s ADHD problem was resolved and her son had no further problems as long as he avoided high phosphate foods. Hafer finds that children with mild ADHD can improve simply by removing processed meats and phosphate-containing beverages like soda and sports drinks from their diets (Waterhouse, 2008).

Everyday plastic products contain hormone-disrupting chemicals, such as Bisphenol A (BPA) and phthalates, that can migrate into our body and affect the brain and nervous system. These environmental toxins bind to zinc and deplete zinc levels in the body. Phthalates are synthetic chemicals used to make plastics soft and flexible. Phthalates are used in hundreds of consumer products and humans are exposed to them daily though air, water, and food. Di(2-ethylhexyl) phthalate (DEHP) is the name for the most common phthalate. It can be found in products made with plastic such as tablecloths, floor tiles, shower curtains, garden hoses, swimming pool liners, raincoats, shoes, and car upholstery. Based on animal studies, the Environmental Protection Agency (EPA) has classified DEHP as a “probable human carcinogen.” Such studies have shown that DEHP exposure affects development and reproduction.

Multiple studies have linked phthalates with ADHD. Researchers assessed the urine phthalate concentrations and ADHD symptoms in 261 children aged 8-11. ADHD symptoms (inattention and hyperactivity/impulsivity), rated by the children’s teachers, were significantly associated with DEHP metabolites (breakdown products) (Kim et al., 2009).

Prenatal phthalate exposure is associated with problems in childhood behavior and executive functioning. Third-trimester urines from 188 pregnant women were collected and analyzed for phthalate metabolites. Their children were assessed for cognitive and behavioral development between the ages of 4 and 9. Phthalate metabolites were associated with worse aggression, conduct problems, attention problems, depression, externalizing problems, and emotional control (Engel et al., 2010).

Exposure to DEHP in pediatric intensive care units (PICU) is associated with attention deficits in children. In the hospital, DEHP can be found in and can leach from medical devices such as catheters, blood bags, breathing tubes, and feeding tubes. Researchers in Belgium measured levels of DEHP byproducts in the blood of 449 children aged 0-16 while they were staying in a pediatric intensive care unit. Four years later, the children’s neurocognitive development was tested and compared to that of healthy children. The researchers found that all medical devices inserted into the body actively leached DEHP. Predictably, hospitalized children had very high levels of DEHP byproducts throughout their stay in the intensive care unit. A high exposure to DEHP was strongly associated with attention deficit and impaired motor coordination four years after hospital admission. Phthalate exposure from the PICU explained half of the attention deficit in post-PICU patients (Verstraete et al., 2016).

BPA is another problem chemical which is found in food and drink packaging. Exposure to BPA may be related to behavior problems in children. A 2016 nationwide study of 460 children aged 8-15 found children with higher urinary levels of BPA had over five times higher odds of being diagnosed with ADHD (Tewar et al., 2016). In another study, researchers measured BPA concentration in urine samples from women at 27 weeks of pregnancy then assessed the behavior of their children at age 6-10. There was a significant positive association in boys between prenatal BPA concentration and internalizing and externalizing behaviors, withdrawn/depressed behavior, somatic problems, and oppositional/defiant behaviors. Researchers speculated that BPA may have disrupted maternal thyroid or gonadal hormones which are critical to proper brain development (Evan et al., 2014).

In addition to heavy metals and plasticizers, pesticides can cause ADHD symptoms. The American Academy of Pediatrics notes, “Children encounter pesticides daily in air, food, dust, and soil. For many children, diet may be the most influential source. Studies link early-life exposure to organophosphate insecticides with reductions in IQ and abnormal behaviors associated with ADHD and autism” (Roberts & Karr, 2012).

Among pesticides, insecticides may be the most harmful to humans. Insecticides were first developed during World War II as nerve gases. They work by targeting and destroying acetylcholinesterase, an enzyme that controls the neurotransmitter acetylcholine which plays a role in attention, learning, and short-term memory. In one study of 307 children aged 4-9, researchers found that lower acetylcholinesterase activity in boys was linked to a four times greater risk of poor attention and executive function and a six times greater risk of memory and learning problems (Suarez-Lopez et al., 2013). Organophosphates (OPs) are a common type of insecticide that target the nervous system. Forty different types of organophosphates are in use in the United States.

Scientists in California studied 320 mothers and their children. They evaluated urinary levels of metabolites of OPs when the mothers were pregnant. Then when the children were 3- and 5- years old, they were evaluated for ADHD. At both time points, levels of prenatal OP metabolites were positively associated with attention problems and ADHD. Children with mothers who had the highest levels of the OP metabolites were five times more likely to develop ADHD (Marks et al., 2010).

Even organophosphate exposure at low levels common among US children may contribute to ADHD prevalence. Researchers at Harvard University studied more than 1,000 children aged 8-15 from the general population and found that those with detectable urinary levels of an OP metabolite were nearly twice as likely to be diagnosed with ADHD (Bouchard et al., 2010).

References:

  1. Braun et al (2006). Exposures to environmental toxicants and attention deficit hyperactivity disorder in U.S. children. Environmental Health Perspectives, 114(12), 1904-1909.

  2. Cecil et al. (2008). Decreased Brain Volume in Adults with Childhood Lead Exposure. PLoS Medicine, 5(5), PLoS Medicine, 2008, Vol.5(5).

  3. Engel et al. (2010). Prenatal phthalate exposure is associated with childhood behavior and executive functioning. Environmental Health Perspectives, 118(4), 565-71.

  4. Evans et al. (2014). Prenatal bisphenol A exposure and maternally reported behavior in boys and girls. Neurotoxicology, 45, 91-99.

  5. Kicinski et al. (2015). Neurobehavioral function and low-level metal exposure in adolescents. International Journal of Hygiene and Environmental Health, 218(1), 139-146.

  6. Kim et al. (2009). Phthalates Exposure and Attention-Deficit/Hyperactivity Disorder in School-Age Children. Biological Psychiatry, 66(10), 958-963.

  7. Kim et al. (2010). Association between blood lead levels (< 5 μg/dL) and inattention-hyperactivity and neurocognitive profiles in school-aged Korean children. Science of the Total Environment, 408(23), 5737-5743.

  8. Ritz, et al. (2012). Phosphate additives in food--a health risk. Deutsches Ärzteblatt International, 109(4), 49-55.

  9. Roberts & Karr. (2012). Pesticide exposure in children. Pediatrics, 130(6), E1765-88.

  10. Rucklidge et al. (2014). Moderators of treatment response in adults with ADHD treated with a vitamin–mineral supplement. Progress in Neuropsychopharmacology & Biological Psychiatry, 50, 163-171.

  11. Sioen et al. (2013). Prenatal exposure to environmental contaminants and behavioural problems at age 7–8years. Environment International, 59, 225-231.

  12. Suarez-Lopez et al. (2013). Acetylcholinesterase activity and neurodevelopment in boys and girls. Pediatrics, 132(6), E1649-58.

  13. Tewar et al. (2016). Association of Bisphenol A exposure and Attention-Deficit/Hyperactivity Disorder in a national sample of U.S. children. Environmental Research, 150, 112-118.

  14. Verstraete et al. (2016). Circulating phthalates during critical illness in children are associated with long-term attention deficit: A study of a development and a validation cohort. Intensive Care Medicine, 42(3), 379-92.

  15. Viktorinova et al. (2016). Changed Plasma Levels of Zinc and Copper to Zinc Ratio and Their Possible Associations with Parent- and Teacher-Rated Symptoms in Children with Attention-Deficit Hyperactivity Disorder. Biological Trace Element Research, 169(1), 1-7.

  16. Waterhouse, J.C. (2008). Issue 6. Review of the Book: The Hidden Drug, Dietary Phosphate: Causes of Behaviour Problems, Learning Difficulties and Juvenile Delinquency (2000). SynergyHN. https://synergyhn.wordpress.com/phosphate

  17. Weiss, G. H., Sluss, P. M., & Linke, C. A. (1992). Changes in urinary magnesium, citrate, and oxalate levels due to cola consumption. Urology, 39(4), 331-333.

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Radio Show Interview about Glyphosate - Dr. William Shaw

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This is a radio show interview with Dr. William Shaw on local New York station WBAI 99.5 from April 15, 2016. Take Charge of Your Health hosts Corinne Funari, RPA, CCN and Linda Segal interviewed Dr. Shaw about the dangers of glyphosate, the world's most widely used herbicide being sprayed on our crops.  To listen to the show, click here.  Dr. Shaw's interview starts at 13:00.

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A New Generation of Organic Acid Testing: Pushing the Limits of Detection with New Technology

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Shaw, William Ph.D

More than 50 phenotypically different organic acidemias have been discovered since the first known disease of this type, isovaleric academia, was described in 1966. An organic acid is any compound that generates protons at the prevailing pH of human blood. Although some organic acidemias result in lowered blood pH, other organic acidemias are associated with relatively weak organic acids that do not typically cause acidosis.

Organic acidemias are disorders of intermediary metabolism that lead to the accumulation of toxic compounds that derange multiple intracellular biochemical pathways, including glucose catabolism (glycolysis), glucose synthesis (gluconeogenesis), amino acid and ammonia metabolism, purine and pyrimidine metabolism, and fat metabolism. The accumulation of an organic acid in cells and fluids (plasma, cerebrospinal fluid, or urine) leads to a disease called organic academia, or organic aciduria.

Although this technology has commonly been used for diagnosing genetic disease in children, genetic diseases in adults have also been detected with it. New applications of organic acid testing include detection of factors in psychiatric disorders, mitochondrial disease and dysfunction, and exposure to a wide variety of toxic chemicals from the environment, and assessment of inflammation due to overproduction of quinolinic acid from tryptophan.

Testing now includes markers for the following metabolites:

  • Glycolysis

  • Krebs Cycle

  • Amino acid Metabolism

  • DNA, RNA metabolism

  • Neurotransmitter metabolism

  • Organophosphate metabolism

  • Yeast, fungal markers

  • Markers for beneficial bacteria

  • Oxalate markers for kidney stones, genetic disease

  • Specific marker for ammonia toxicity

  • Markers of fatty acid catabolism

  • Metabolic diseases causing autism spectrum disorders

  • Phthalates

  • Solvents

  • Pyrethrins

  • Dry cleaning solvents

  • Preservatives

  • Vinyl chloride

  • Specific Clostridia marker

  • Specific mitochondrial disease markers

  • Vitamin deficiency markers

  • Phosphate marker of bone function

  • Marker for glutathione precursor

  • Genetic screening with extremely sensitive markers

Organic acids are most commonly analyzed in urine because they are not extensively reabsorbed in the kidney tubules after glomerular filtration. Thus, organic acids in urine are often present at 100 times their concentration in the blood serum and thus are detected in urine with greater accuracy and precision than with blood samples. The number of organic acids found in urine is enormous: over 1000 have been detected since this kind of testing started 25 years ago. The challenge of dealing with so many compounds led to the use of gas chromatography-mass spectrometry (GC/MS) to analyze these complex body fluids.

With GC/MS, organic acids are chromatographically separated on the basis of their polarity and volatility and then bombarded by an electron beam that fragments the eluting molecules in a characteristic pattern. The patterns, or spectra, are stored by a computer system and then compared with known spectra that are compiled in a spectral "library." The software then compares an unknown spectrum to all the spectra on the hard drive and prints out those with the best fit. Since a single organic acid analysis generates over 1000 spectra, and each spectrum may consist of 600 ions, the software must be optimized to analyze the data in the most efficient and clinically relevant manner. Recently, the Great Plains Laboratory Inc. increased the sensitivity of this technology by approximately 1000-fold with the use of new triple-quadrupole MS technology so that a large number of toxic compounds can be measured at levels of micromoles/mole creatinine compared with urine compounds, such as vanillylmandelic (VMA), which is measured at levels of millimoles/mole creatinine.

The scope of organic acid testing has been markedly widened by commercial laboratories such that it can monitor physiological changes in nongenetic diseases and offer tremendous help in diagnosis and treatment of most chronic illnesses. Some examples are given below:

An adult with a movement disorder and bilateral temporal arachnoid cysts by brain imaging was found to have very elevated glutaric acid, indicating the presence of the genetic disease glutaric aciduria type 1.1Symptoms of this potentially fatal disorder include headaches, ataxia, memory loss, and many other neurological effects. Treatment with high doses of carnitine may be helpful in relieving symptoms in such cases, and of course such information is important for genetic counseling.

High levels of urine oxalates in an adult with frequent kidney stones led to a closer examination of the patient's dietary history. The patient ate a large spinach salad with pecans almost every day. Spinach is one of the foods highest in oxalates, and all nuts are high in oxalates as well. Treatment is directed at reducing dietary oxalates as well as calcium citrate and vitamin B6 supplementation.

After organic acid testing, a child with autism was found to have very high values (more than four times the upper limit of age-appropiate normals) of the catecholamine metabolites VMA and HVA, indicating a possible neuroblastoma. Follow-up imaging near the spine confirmed the presence of a previously undiagnosed neuroblastoma, likely saving the child's life.

Another child thought to have autism had very low amino acids, and the neurologist recommended high doses of amino acid supplements, which made the child severely ill. Organic acid testing revealed a massive excretion of methylmalonic acid, indicating that the child had methlmalonic aciduria, a severe genetic disorder. Treatment of this disorder requires extensive supplementation with vitamin B12 and a low-protein diet. Continued amino acid supplementation or a high-protein diet might have been fatal.

A person with severe depression was found to have low amounts of the serotonin metabolite 5-hydroxy-indoleacetic acid, which is derived from tryptophan. Depression is associated with decreased brain serotonin. However, the tryptophan metabolite by an alternate pathway, quinolinic acid, was much higher. Quinolinic acid is associated with inflammation such as arthritis and is considered to be neurotoxic, with a probable role in Parkinson's syndrome, Alzheimer's disease, Huntington's disease, and schizophrenia.2,3 The condition eosinophilia myalgia syndrome (EMS), associated with excessive tryptphan intake, is probably not due to tryptophan itself but to the inflammatory effects of its major metabolite quinolinic acid. Quinolinc acid administered by itself generated all of the symptoms of EMS.4,5 This research indicates that various conspiracy theories about contaminated tryptophan batches as the cause of EMS are unnecessary and probably wrong. 100% pure tryptophan at high enough doses will produce significant quantities of toxic quinolinic acid and EMS in susceptible individuals. Administration of 5-hydroxytryptophan (5-HT or 5-HTP) is a much safer option than tryptophan since 5-HT cannot be converted to the neurotoxic quinolinic acid, whereas only about 1% of tryptophan is converted to serotonin.6 Both the serotonin metabolite and quinolinic acid are measured by organic acid testing (Figure 1).

I recently proved that the dibiosis marker 3-(3-hydroxyphenyl)-3-hydroxypropionic acid (HPHPA), the predominant dihydroxy-phenylpropionic acid isomer in urine measured in the organic acid test, is due to a combination of human metabolism and the metabolism by a group of Clostridia species, including but not limited to C. difficile.7 The same article indicates that 3,4-dihydroxyphenylpropionic acid (DHPPA) is a marker for beneficial bacteria in the gastrointestinal tract such as Lactobacilli, Bifidobacteria, and E. coli. The exception is one species of Clostridia orbiscindens that can convert the flavonoids luteolin and eriodictyol (which occur only in a relatively small food group that includes parsley, thyme, celery, and sweet red pepper) to DHPPA. The quantity of C. orbiscindens in the gastrointestinal tract is negligible (approximately 0.1% of the total bacteria) compared with the predominant flora of Lactobacilli, Bifidobacteria, and E. coli.7 DHPPA is an antioxidant that lowers cholesterol, reduces proinflammatory cytokines, and protects against pathogenic bacteria.

Outdated literature has referred to HPHPA as due to dietary origin based mainly on conjecture, but this conjecture was clearly disproved by my 2010 article which indicates that the metabolite is abolished by the antibiotic metronidazole.8 DHPPA, a different isomer, has been claimed to be a metabolite of Pseudomonas species, but the literature indicates that this compound is formed by the in vitro action of these species on quinolone, a component of coal tar – a substance missing from the diet of virtually all humans.9

HPHPA has been one of the most useful clinical markers in recent medical history. Treatment of individuals with high urinary values with metronidazole, vancomycin, or high doses of probiotics has led to significant clinical improvements or remissions of psychosis, tic disorders, seizures, autistic behaviors, hyperactivity, chronic fatigue syndrome, and obsessive compulsive behavior.

One of the newest aspects of organic acid testing is the screening for 74 different toxic chemicals in the environment by testing their organic acid metabolites. Solvents such as benzene, toluene, styrene, and others may be present for only short periods in body fluids and may also be lost in transit due to their volatility, but their metabolites are very stable. Using this screening technique, most metabolites of different organophosphates and pyrethrins can be measured as well as trichloroethylene, tetrachloroethylene, and vinyl chloride. Phthalates, an extremely toxic group of compounds implicated in infertility and abnormal sexual development in both males and females, can be measured by their metabolite phthalate, a specific chemical entity.

The chemical structure of phthalic acid (or phthalates) is nearly identical to quinolinic acid. A toxic effect occurs when phthalic acid competitively inhibits the reaction by which quinolinic acid is converted to the beneficial coenzyme NAD. High concentrations of phthalic acid or quinolinic acid may be associated with increased toxicity due to phthalate blockage of NAD formation and potential mitochondrial dysfunction due to deficient NAD for mitochondrial energy production.

One of the most important advances in the organic acid test is the addition of a biochemical marker, tiglylglycine, as a specific indicator for mitochondrial dysfunction.11 Mitochondrial dysfunction has been implicated in Parkinson's and Alzheimer's syndromes, diabetes, autism, chronic fatigue syndrome, aging, and many others. Tiglylglycine has been shown to be elevated in the urine in mitochondrial disorders involving defects of complexes I, II, III, and IV, protein complexes attached to the mitochondrial membrane that are involved in energy production. In addition to mutations in mitochondrial or nuclear DNA, mitochondrial dysfunction may also be due to exposures to toxic chemicals such as organophosphates and the solvent trichloroethylene. The advantage of the organic acid test is that if a mitochondrial dysfunction is detected, a number of different toxic chemicals implicated in mitochondrial damage can be reviewed to find the potential cause. Trichloroethylene has been found as a contaminant in the municipal water supply of many cities in both the US and Canada, and is used as a degreaser military bases and as a common solvent throughout the chemical industry. Mitochondrial disorders can be treated with a cocktail of nutritional substances including coenzyme Q10, carnitine, riboflavin, and others, when chemical exposure is not detected. If toxic chemicals are found, treatment with the Hubbard protocol can be highly successful for the removal of a wide array of toxic substances.12

Clinical References:

  • 1. Martinez-Lage J et al. Macrocephaly, dystonia, and bilateral temporal arachnoid cysts: glutaric aciduria type 1. Childs Nerv Sys. 1994;10(3): 198-203.

  • 2. Guillemin GJ et al. Quinolinic acid in the pathogenesis of Alzheimer's disease. Adv Exp Med Biol. 2003;527:167-176.

  • 3. Stoy N et al. Tryptophan metabolism and oxidative stress in patients with Huntington's disease. J Neurochem. 20015;93:611-623.

  • 4. Silver RM et al. Scleroderma, fasciitis, and eosinophilia associated with the ingestion of tryptophan. N Engl J Med. 1990;322(13):874-881.

  • 5. Noakes R, Spelman L, Williamson R. Is the L-tryptophan metabolite quinolinic acid responsible for eosinophilic fasciitis? Clin Exp Med. 2006;6(2):60-64.

  • 6. Shah GM et al. Biochemical assessment of niacin efficiency among carcinoid cancer patients. Am J Gastroenterol. 2005;100:2307-2314.

  • 7. Shaw W. Increased urinary excretion of a 3-(3-hydroxyphenyl)-3-hydroxypropionic acid (HPHPA), an abnormal phenylalanine metabolite of Clostridia species in the gastrointestinal tract, in urine samples from patients with autism and schizophrenia. Nutr Neurosci. 2010;13(3):1-10.

  • 8. Kumps A, Duez P, Mardens Y. Metabolic, nutritional, latrogenic, and artifactual sources of urinary organic acids: a comprehensive table. Clin Chem. 2002,48:708-717.

  • 9. Shukla OP. Microbial transformation of quinolone by a pseudomonas sp. Appl Environ Microbiol. 1986;51(6):1332-1342.

  • 10. Fukuwatari T et al. Phthalate esters enhance quinolinate production by inhibiting alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarbocylase (ACMSD), a key enzyme of the tryptophan pathway. Toxicol Sci. 2004;81:302-308.

  • 11. Bennett M et al. Tiglylglycine excreted in urine in disorders of isoleucine metabolism and the respiratory chain measured by stable isotope dilution GC-MS. Clin Chem. 1994;40(10):1879-1833.

  • 12. Shaw W. The unique vulnerability of the human brain to toxic chemical exposure and the importance of toxic chemical evaluation and treatment in orthomolecular psychiatry. J Orthomol Med. 2010;25(3).