A faulty gene may be responsible for some cases of sudden infant death syndrome (SIDS), also known as crib or cot death, U.S. researchers said on Monday.

Tests on Amish families from Pennsylvania turned up a new disorder that causes sudden death and sometimes malformation of the genitals, the researchers report in this week’s issue of the Proceedings of the National Academy of Sciences.

The finding could help explain some of the inexplicable, unexpected deaths of 3,000 infants a year in the United States and thousands elsewhere around the world.

The researchers have named their newly found disorder sudden infant death and dysgenesis of the testes syndrome or SIDDT. Babies must inherit two flawed copies of the gene to develop symptoms, which include organ dysfunction.

They die before they are a year old from sudden cardiac and respiratory failure.

In two generations, 21 infants from the Belleville Amish community in southeastern Pennsylvania have died from SIDDT, Dietrich Stephan of the Translational Genomics Research Institute in Phoenix, Arizona and colleagues at the Clinic for Special Children in Strasburg, Pennsylvania reported.

To find the gene, they analyzed DNA from four affected infants, as well as from their parents, siblings, and other relatives.

Males with SIDDT may have underdeveloped testes. Girls appear normal and have normal female hormones, yet both male and female infants with SIDDT die suddenly at the same age.

“One infant died in the hospital while awake and attached to a cardiac-respiratory monitor,” the researchers wrote. The monitor showed the child’s heart and breathing function stopped suddenly at the same moment.

“Another infant died suddenly and unexpectedly at home, with no premonitory signs. In both cases, neuropathological examinations were done by experts in sudden infant death syndrome. Brain and peripheral nerves were normal,” the researchers added.

“This is one of the first genetic sub-classifications of SIDS,” Stephan said in a statement. “And it’s going to be helpful in offering parents answers for sudden infant deaths, recognizing predisposition early, and hopefully saving a number of these babies.”

While SIDS is a general term for such deaths, doctors suspected different causes may be at fault.

For example, campaigns in Britain and the United States to educate parents and caretakers to put babies down to sleep on their backs instead of their tummies cut SIDS deaths in half, but did not eradicate them.