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j. Gastrointestinal Function
Many if not most autistic individuals have gastrointestinal problems, the most common complaints being chronic diarrhea, constipation, gaseousness, and abdominal discomfort and distention (D’Eufemia et al, 1996; Horvath et al, 1999; Whitely et al, 1998). Colitis is not uncommon (Wakefield et al, 1998). As noted previously, anorexia is sometimes associated with ASD (Gillberg & Coleman, 1992). Kanner noted that over half his initial cases had feeding difficulties and excessive vomiting as infants (1943). O'Reilly and Waring (1993) have described sulfur deficiencies in autism, an effect of which can be clumping of proteins on the gut wall, which is lined with sulfated proteins. The clumping can lead to increased intestinal permeability, or leaky gut syndrome (Shattock, 1997), found in many autistic individuals (D'Eufemia, 1996). Some ASD individuals have unusual opioid peptide fragments in urine; these peptides are believed to enter the bloodstream due to a leaky gut and to result from an incomplete breakdown of gluten and casein in the diet possibly arising from "inadequacy of the [endopeptidase] enzyme systems which are responsible for their breakdown" (Shattock, 1997).
Mercury, which binds to sulfur groups (Clarkson, 1992), is known to cause gastroenteritis (Kark et al, 1971). For example, a four year old with diarrhea was initially diagnosed with gastroenteritis (Florentine and Sanfilippo, 1991). A pre-adolescent with mercury vapor poisoning developed nausea, abdominal pain, poor appetite, rectal itching, and diarrhea; she frequently strained to have a bowel movement, and was at one point diagnosed with colitis (Fagala and Wigg, 1992). Acrodynia is marked by both constipation and diarrhea (Diner and Brenner, 1998). Incontinence of urine and stool are observed in infants and children exposed pre- and postnatally in Iraq (Amin-Zaki, 1974 and 1978). In another case, a 28 year old woman with occupational exposure to mercury vapor developed watery stools (Ross et al, 1977). Diarrhea and digestive disturbance were seen in a dentist with measurable mercury levels; there was obesity in another dentist (Smith, 1977). A 44 year old man poisoned with thimerosal given intramuscularly developed gastrointestinal bleeding, which looked like hemorrhaging colitis (Lowell et al, 1996). Intense exposure to mercury vapor can cause abdominal pain, nausea, and vomiting (Feldman, 1982). Severe constipation, anorexia, weight loss, and other “disturbances of gastrointestinal function” have been noted in other cases (Adams et al, 1983; Joselow et al, 1972). Rats tested with mercuric chloride were observed with “lesions of the ileum and colon with abnormal deposits of IgA in the basement membranes of the intestinal glands and of IgG in the basement membranes of the lamina propria” (Andres, 1984, reviewed in EPA, 1997, p.3-36). In another rat experiment, Hg was found to increase the permeability of intestinal epithelial tissues (Watzl et al, 1999). Mercury also inhibits the peptidase - dipeptidyl peptidase IV - which cleaves, among other substances, casomorphin during the digestive process (Puschel et al, 1982).
There is no reported increase in incidence in kidney problems in autism. Although renal function is commonly impaired from Hg exposure, such impairment would not be expected if the mercury exposure occurred from thimerosal injections, since kidney function may be unaffected when mercury is injected or inhaled (Davis et al, 1994; Fagala and Wigg, 1992). For example, although thimerosal ingested orally by a 44 year old man resulted in renal tubular failure and gingivitis (Pfab et al, 1996), renal function was normal in another 44 year old man injected intramuscularly with thimerosal (Lowell et al, 1996).