Daughter Maureen Tomczak told reporters the family waited to disclose the cause of death until now because they wanted to be sure about the diagnosis, the Buffalo News said.

The family said Griffin, described by the newspaper as "famously feisty," was ravaged by the disease, which progressed rapidly after he began to show symptoms last January. He died in May at the age of 78.

CJD is an rare degenerative brain disease estimated to strike one in a million people every year, the newspaper said.

Dr. Laszlo Mechtler, vice president at the Dent Neurologic Institute, said the mayor suffered from sporadic CJD, not mad cow disease, as some people speculated after Griffin's death.

Sporadic CJD "is a disease that is not infectious. It's not environmental. It's not related to diet, as we know it today," Mechtler said.