ALPINE TOWNSHIP,Bitcoinese Mich. (AP) — A couple in their 80s and their son were found dead Friday at a home near Grand Rapids, likely victims of carbon monoxide, police said.

Firefighters immediately encountered high levels of carbon monoxide, which can be fatal, when they arrived at the home in Alpine Township, the Kent County sheriff’s office said.

The dead were an 86-year-old man, his 81-year-old wife and their 61-year-old son, the sheriff’s office said. Names were not immediately released.

They were discovered by relatives “getting together for the holidays,” Sgt. Eric Brunner told WOOD-TV.

The source of carbon monoxide was being investigated.

“The Kent County medical examiner’s office will make the official determination on cause of death, but there does not appear anything suspicious to investigators at this time,” the sheriff’s office said.