Passage: Where no family history of the disease is present — around 90% of cases — no cause is known. Possible associations for which evidence is inconclusive include military service and smoking. Although studies on military history and ALS frequency are inconsistent, there is weak evidence for a positive correlation. Various proposed factors include exposure to environmental toxins (inferred from geographical deployment studies), as well as alcohol and tobacco use during military service.A 2016 review of 16 meta-analyses concluded that there was convincing evidence for an association with chronic occupational exposure to lead; suggestive evidence for farming, exposure to heavy metals other than lead, beta-carotene intake, and head injury; and weak evidence for omega-three fatty acid intake, exposure to extremely low frequency electromagnetic fields, pesticides, and serum uric acid.In a 2017 study by the United States Centers for Disease Control and Prevention analyzing U.S. deaths from 1985 to 2011, occupations correlated with ALS deaths were white collar, such as in management, financial, architectural, computing, legal, and education jobs. Other potential risk factors remain unconfirmed, including chemical exposure, electromagnetic field exposure, occupation, physical trauma, and electric shock. There is a tentative association with exposure to various pesticides, including the organochlorine insecticides aldrin, dieldrin, DDT, and toxaphene.

Question: When there is no family history of disease then the cause if what?
no cause is known