Very large bone-marrow cells are showing up in the brains of people who died of COVID-19, which may help explain some of the neurological problems associated with the disease, according to researchers.

The cells, called megakaryocytes, normally reside in the bone marrow and make platelets for blood clotting.

“We found that in some patients who died of COVID-19, the capillaries - the smallest blood vessels - contained very large cells called megakaryocytes,” study leader David Nauen of Johns Hopkins University told Reuters.“They are so large they could be occluding blood flow through the capillaries and limiting oxygen delivery to the brain, which could impair brain function.”

As reported  in the journal JAMA Neurology, his team studied brain tissue from 15 patients who died of COVID-19 and found megakaryocytes in five of their brains. “What signaled these cells to leave the bone marrow and travel to the brain is unknown, but COVID-19 causes disruptions of the clotting system, and it’s possible this is related,” Nauen said.