Could you tell me what is the name of the defect that causes non-inherited genetic diseases?

No one name: There is no one defect/name that causes non-inherited genetic diseases. One example is a "de novo" genetic disease. This happens in many disorders in which the mutation or a deletion of a gene (or genes) happens for the first time in the child and is not present in either parent. Thus it was not inherited from parent. But this child could pass it on and it would be inherited in his/her children.

Spontaneous mutation: Some inheritable disorders are also caused by spontaneous mutations. Advanced paternal age ^es risk. Nondisjunction = paired chromosomes don't separate during cell division. The fetus receives 2 or 0 copies from egg or sperm. Advanced maternal age ^es risk. . Copy repeat errors are similar, when baby inherits 0 or 2 copies of a small sequence of genes from mom or dad.

Epigenetics: Not only do we have about 20,000 genes which have all the information guiding a fertilized egg into an adult, we are now learning about all the non-genetic factors which can interfere with the regulation of these genes, called epigenetics--switching them on or off too soon, and a host of substances which can interfere with normal development and function. There are potentially millions.