Four-year-old Cameron Stevens, and his seven-year-old brother Brandon from Wales, are believed to be the only siblings in the world to be diagnosed with an extremely rare life-threatening condition.
Both suffer from Nuclear Factor Kappa B Essential Modulator, or Nemo for short.
So rare is the disorder that there has been only one previous case recorded in Wales.
Parents Andrew and Katherine discovered that the boys had the condition two years ago having been baffled by their sons' thinning hair, pointed teeth and dry skin, all symptoms of the disorder.
Tests also revealed that Katherine was a carrier for the Nemo gene.
"It is a one-in-three chance that I passed it on and I have passed it onto both of them," she said. "That is life. As far as I know they are the only siblings in the world to have Nemo."
Although the condition can be life-threatening, doctors are pleased with the boys' progress.
Brandon and Cameron steer clear of poorly friends to reduce the chances of infection. They also take antibiotics twice daily and have weekly infusions of haemoglobin to support their immune system, weakened by the condition.
Mother Katherine had no idea she was a carrier of the Nemo gene before she had children but with over 4000 known inherited genetic disorders, there is the possibility anyone of us could unknowingly pass on a disorder, even if previous children are born perfectly healthy.
If you are a carrier of a defective gene, there is still only a mathematical chance that you will pass it on to your children. Genetic testing is becoming increasingly available for those thought to be in high-risk groups.
Some would say the Stevens' have been unlucky to have both their boys inherit Nemo, others would say they are lucky to have two lovely, beautiful sons.
If you were planning to start a family would you want to know the risks of passing on a disorder to your baby, or should nature be left to take its course?