A number of studies have indicated that exposures to chemicals and other agents, such as ethylnitrosourea and radiation, can cause mutations in male germ cells. Epidemiological investigations have linked paternal occupational and environmental exposures to mercury, lead, solvents, alcohol, cigarette smoking, and other compounds to spontaneous abortion, low birth weight, and birth defects. Advanced paternal age is a factor for an increased risk of limb and neural tube defects, Down syndrome, and new autosomal dominant mutations. Interestingly, men younger than 20 also have a relatively high risk of fathering a child with a birth defect. Even transmission of paternally mediated toxicity is possible through seminal fluid and from household contamination from chemicals brought home on workclothes by the father. Studies also show that males with birth defects themselves have a greater than twofold risk of having an affected child.
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