Casey Johnson died of natural causes, the Los Angeles coroner has ruled.

The specific cause of death was "diabetic ketoacidosis," a condition caused by a shortage of insulin, according to a coroner statement.

The Johnson & Johnson heiress, 30, who recently got engaged to reality TV star Tila Tequila, was found dead in her L.A. home on Jan. 4.

Johnson had suffered from severe diabetes since childhood.

Shortly after her death, a law enforcement source told PEOPLE that hypodermic needles were found in the home, and they suspected Johnson partied the night before she died and neglected to take her insulin. No illicit drugs were found.

The heiress left behind her adopted daughter, Ava, 3, who will live with Johnson's mother Sale and her husband Ahmad Rashad "for the foreseeable future," according to a family source. – Ken Lee