Complications from acute myeloid leukemia was Nora Ephron's cause of death, but the average news consumer knows very little about the serious condition.

One of the most common forms of adult leukemia, acute myeloid leukemia (AML) is a cancer that starts in the bone marrow and develops quickly, according to the U.S. National Library of Medicine. Bone marrow, the soft tissue found in the middle of bones, create blood cells.

AML forms from abnormal cells in their bone marrow that are supposed to turn into disease-fighting white blood cells. The abnormal cells grow rapidly (acute means fast-developing) and replace normal, healthy blood cells.

Rarely found in people below the age of 40 years old, it is typically found in people about 60 years old, and it is more common in men than women.

The symptoms of acute myeloid leukemia can be very serious, as it can cause its sufferers' immune systems to be severely weakened as it stops bone marrow from working properly. That appears to be what occurred in the case of Nora Ephron, who died of pneumonia that arose out of complications with her AML.

The range of symptoms include increased bleeding and bruising, bone pain, fatigue, fever, rashes, weight loss and more.

Acute myeloid leukemia can be caused by exposure to some chemicals such as benzene, some chemotherapy drugs and radiation, while there is a genetic component to AML.

People with certain other medical problems can also be at heightened risk for developing acute myeloid leukemia. One such condition is myelodysplasia, a condition that Nora Ephon's close friend, Washington Post columnist Richard Cohen, told the paper that she suffered from after being diagnosed with it six years ago.

There are eight types of AML. As of now it is not publicly known which type Nora Ephron suffered from.

Chemotherapy is the main method of fighting acute myeloid leukemia, but antibiotics, bone marrow/stem cell transplants, blood transfusions and other treatments are also used to help treat the condition.

CBS News reported Tuesday evening that Ephron's oncologist, Dr. Gail Roboz, told the network that she died at Weill-Cornell/New York-Presbyterian at 7:40 p.m. EDT from acute myeloid leukemia.

The 71-year-old screenwriter was best known for winning movie-goers' hearts by writing ultra-popular romantic comedies like When Harry Met Sally, Sleepless In Seattle and You've Got Mail.

Nora Ephron was one of the film industry's most powerful and moving screenwriters, and even beyond that there is almost no limit to the things she did and experienced in her life, from being nominated for three Academy Awards to working as a reporter for a time at the New York Post to being one of the few people to know the identity of Deep Throat (Mark Felt) before her ex-husband Carl Bernstein revealed that information publicly several years ago.

In recent years she continued to write despite her sickness, and several years ago she began writing an occasionally updated blog for the Huffington Post, where she is still listed as an Editor at Large.

She moved in the highest circles of New York City society, and she wrote with an authority and panache that made her one of the all-time highest-grossing screenwriters.

Nora Ephron is survived by her third husband, author and screenwriter Nicholas Pillegi. The two had been married since 1989.