A mysterious cluster of deaths among Amish children 15 years ago may finally have been solved.

Doctors were baffled by the deaths, which cropped up in multiple states including Pennsylvania, Delaware, Kentucky, and Iowa.

In each event, the otherwise healthy boys and girls were running about or playing when they suddenly passed away from heart failure.

When their autopsies came back negative for any known cause of death, baffled coroners reached out to geneticists.

Even the lab they went to, which specialises in unexplained deaths, could not figure out what had caused their heart failure.

But now the same scientists investigating the spate of deaths have now found the youngsters all shared a faulty gene mutation.

In 2004 a cluster of child deaths in Amish communities baffled scientists. The children dropped dead suddenly while playing (stock)

The team at Windland Smith Rice Sudden Death Genomics Laboratory say they all had specific defects of the RYR2 gene.

RYR2 is a protein found primarily in heart muscle. The mutation appears to cause the heart to suddenly stop beating when heart rate is elevated.

The first death happened in 2004 in Rochester, Minnesota when a 12-year-old girl dropped dead suddenly while playing. Her younger sister died under similar circumstances months later.

WHAT KILLED THE CHILDREN? In each event, the otherwise healthy boys and girls were running about or playing and were not doing anything particularly dangerous. Their hearts suddenly stopped beating when heart rate was elevated. Scientists found they all shared a faulty RYR2 gene. RYR2 is a protein found primarily in heart muscle. The mutation appears to cause the heart to suddenly stop beating when heart rate is elevated The team found more than 300,000 segments of the RYR2 gene had become duplicated. The defect can be passed down only if both birth parents had them.

But the scientists were unable to notice these tiny changes inside the gene because technology was only able to look at one gene at a time.

Four more similar deaths last year allowed researchers to look again. Advanced technology meant they could peer inside each gene and look at individual strands of DNA.

The Wind team, part of the Mayo Clinic, found more than 300,000 segments of the RYR2 gene had become duplicated.

Experts say the defect has only occurred in Amish children because of their tight-knit communities and they only intermarry with one another.

The defect can be passed down only if both birth parents had them.

And the mother and father can both live completely healthy without it having any effect on their health.

The Amish are a group of traditionalist Christian church fellowships known for simple living, plain dress, and reluctance to use modern technology.

Michael Ackerman, director of the Mayo Clinic Windland Smith Rice lab, said there is only one known treatment for the defect – an Implantable Cardioverter Defibrillator.

An ICD is a small battery-powered device placed in your chest to monitor heart rhythm and detect irregular heartbeats.

It can deliver electric shocks via one or more wires connected to keep the heart beating when its muscles stop.

The researchers say they are working toward a screening test for couples who don’t want to pass on the genes to their offspring.

Dr Ackerman and his colleagues published their findings in JAMA Cardiology.