INTRODUCTION: Mental Retardation
Mental retardation (MR), defined as a failure to develop a sufficient cognitive and adaptive level. It is one of most common human disease. Also, 1-3 % of the human population has an IQ below 70. Recent research has discovered that MR is related to the presence of certain mineral elements in the body above-normal levels, especially cadmium and lead (Mike et al. 1983). It has been estimated that half of all cases are due to environmental factors, that include prenatal exposure of the fetus to toxic substances, environmental contaminants, infections, radiations, illness of mother (eg exposure to rubella, Cytomegalovirus) and malnutrition etc. (Birgitta et al. 2003). The prevalence of Intellectual disability (ID) also referred to as mental retardation is between 1% and 3% (Roeleveld et al. 1997; and Wen 2002). And ID is present in every social class and culture (Leonard and Wen 2002). Also, there are approximately 30% more males with MR are diagnosed than females (American Psychiatric Association 2000; Miclaren and Bryson 1987). Alzheimer’s disease (AD) is a mental retardation mostly caused by cadmium. Also, blood cadmium concentration in Alzheimer’s disease and non-demented subjects were studied. Smokers had higher cadmium level than non-smokers.
It is a clear, colorless fluid formed in the ventricles of the brain mainly by choroid plexus (an interlaced structure or meshwork of tiny small blood vessels in the lateral third and fourth ventricles). It is mainly an ultrafiltrate of plasma.
Waste products excreted from the digestive tract are composed of water (up to 75%), indigestible residue, undigested food, food which is digested but not absorbed, bile, epithelial cells, secretions from the digestive tract, inorganic material, and bacteria. The normal amount of feces in an adult is 100-200 grams per day. Examination of feces is helpful in the investigation of diseases of the gastrointestinal tract.