DISTRIBUTOR: ITV GLOBAL
American children Danny, Hannah, Bradley, and Bri, are four of the smallest people in the world.
Their syndrome is the rarest of all the 200 types of dwarfism, and is characterised by tiny stature, a high-pitched squeaky voice, and limited life expectancy.
Primordial dwarfs are also the smallest of all those affected by any one of the different types of dwarfism.
The syndrome is caused by a recessive gene, and all primordial dwarves are born to average-sized parents who are both carrying it.
The gene is so rare it is yet to be identified. There is estimated to be roughly 100 primordial dwarves living in the world, with 40 of them based in the US.