genetic cracker: There's hope for people suffering from Huntington's disease. The lethal disease is programmed in the genes and appears at a predictable age in adulthood, causing a decline in mental functions and finally death. Such diseases are caused by an unusual genetic mutation; a three-letter piece of the gene code is repeated over and over in one gene. Scientists at the Weizmann Institute in Israel have proposed a mechanism that explains this. They say that the move may help researchers find a possible cure for the lethal disease.