A compound that inhibits the cellular expression of a nucleotide sequence corresponding to all or part of the presenilin 1 gene, the compound comprising an antisense molecule comprising the antisense of a polynucleotide sequence selected from the group consisting of the entire polynucleotide sequence of the presenilin 1 gene, a fragment of the sequence of the presenilin 1 gene, the promoter or other regulatory sequence of the presenilin 1 gene and a polynucleotide sequence that is at least 90% homologous to the polynucleotide sequence of the presenilin 1 gene is described. Pharmaceuticals containing and methods of inhibiting the presenilin 1 gene using such compound are also described. A compound and method of inhibiting the expression product of the presenilin 1 gene also is described. A method of treating a patient having a condition characterized by excessive cell growth also is described. A method of diagnosing cancer also is described. A method of screening drugs that inhibit the presenilin 1 gene also is described. A compound and pharmaceutical that activates the presenilin 1 gene also is described as is a method of treating diseases associated with cell death.