In City of Portsmouth Sheriff's Dept. v. Clark, 30 Va. App. 545, 518 S.E.2d 342 (1999), the Court held that proof of a "risk factor" alone does not establish a non-work-related cause for a claimant's heart disease. Portsmouth, 30 Va. App. at 554, 518 S.E.2d at 346. The Court found that the employer in that case had failed to prove that the claimant's family history risk factor actually caused his disease. Id.