Nancy Guthrie, 84, vanished from her home in the Tucson, Ariz., area on Feb. 1, and the case remained unsolved more than a month later, the Associated Press reported. Her daughter, NBC “Today” co-host Savannah Guthrie, has made repeated public appeals and offered a $1 million reward for information. The disappearance has drawn attention to what researchers call ambiguous loss — a form of psychological suffering caused by an unresolved absence that leaves families neither able to mourn nor to stop hoping.

Ambiguous loss, a clinical term coined in the 1970s, describes the particular grief of families whose loved ones disappear without explanation. Researchers say it is among the most psychologically painful experiences humans endure, and the Nancy Guthrie case has put a public face on a condition shared by many thousands of families across the country.

The Guthrie disappearance

Savannah Guthrie said her mother was “taken in the dark of night from her bed.” More than a week after the disappearance, the FBI released video from a camera outside Nancy Guthrie’s front door showing a masked stranger at the home. Her blood was found on the porch, the AP reported. The case remains unsolved.

Guthrie appeared on camera Feb. 24, her eyes red, and quoted her sister: “As my sister says, ‘We are blowing on the embers of hope.’”

The family announced it would donate $500,000 to the National Center for Missing & Exploited Children, citing “millions of families that have suffered” similar uncertainty.

What researchers say

The term “ambiguous loss” was coined by Pauline Boss, a family therapist who in the 1970s interviewed women in California whose husbands were missing in action in the Vietnam War. Boss and Tai Mendenhall, a medical family therapist at the University of Minnesota, later worked with families following the Sept. 11, 2001, attacks at New York’s World Trade Center.

The condition can arise from abductions, runaways, certain natural disasters, and war. Dementia — when family members become strangers — also fits the category.

“They’re frozen in their grief,” Mendenhall said. “They have a real sense of helplessness. There’s no clear resolution from it. We know from research that ambiguous loss is the most psychologically painful kind of loss because of that.”

Another family’s 18-year wait

Lynette Pino, 58, of Tesuque Pueblo in New Mexico, watched coverage of the Guthrie case and recognized what the family was experiencing. Her son, Darian Nevayaktewa, has been missing for nearly 18 years.

Nevayaktewa was 19 in June 2008 when he left to visit his father on the Hopi reservation in Arizona and did not return.

“He wanted to go see his dad on the Hopi reservation in Arizona,” Pino said. “I just remember that day hugging him, telling him he only needed a half-semester to graduate from high school. He wasn’t there long, maybe a week, before he disappeared. Someone took him somewhere — I don’t know. Hard to say.”

Nevayaktewa’s case is among many unsolved disappearances in Native American communities. The FBI said last year it was sending extra agents, analysts and other personnel to 10 states to address violent crime in those communities.

“I could see in their faces that they want answers,” Pino said of the Guthries. “What’s the next step? What can we do? It’s how I feel. There are no answers.”

Faith and community as supports

Savannah Guthrie has referred publicly to her Christian faith, asking followers on Instagram to “raise your prayers with us” and recently suggesting her mother might be in heaven dancing “with our daddy.” Mendenhall said that response is a recognized source of resilience.

“When people turn toward their faith, that is where they find solace,” Mendenhall said. “Oftentimes the power of faith comes from the communities that inhabit it. Sometimes the best treatment for ambiguous loss is a community group, people who have had this shared experience.”

Pino said she regularly turns to prayer and lit candles for Nevayaktewa during a trip to Arizona last summer. Her message to the Guthries: “Do not give up hope. Don’t let law enforcement put it aside.”