A puzzling discovery made in 1993, was that the mutant gene causing Huntington's disease is longer than the normal gene. The DNA sequence CAG is repeated a few times in the non-nal gene but in the mutant gene this sequence is repeated hundreds of times. No one yet knows how this expan- sion can happen or why it is deleterious. Therefore radioactivity, UV irradiation, and contact with mutagenic substances, such as aflatoxin, should be avoided. There are hundreds if not thousands of chemicals which cause mutation in our world.
Chemicals are mutagenic also cause cancer.
How much of any mutagen is harmful and what is the acceptable limit to release the environment is the subject of long debate and argument between ntists, environmentalists, industrialists and politicians. We can probably do very little about this, we should do our best to exclude mutagens from the environment. There are a number of distinct strategies for dealing with genetic disease. Foetuses may be genetically screened and abortion of affected foetuses offered. This approach causes problems as abortion is unacceptable to many persons.