According to the Stuff website, rheumatic fever nearly claimed his life at 13, yet he showed a decade of fight to win a Melbourne Storm rugby league contract, then one with the Blues in Super Rugby.
Now its effects have struck again.
Johnson has a lengthy scar down the centre of his chest as a constant reminder of what he has faced and is facing again. He is in intensive care.
Now 26, the Manurewa-raised footballer has already had two heart operations.
His Melbourne Storm days were cut short by the club after nine months due to his heart condition.
Nine months into a two-year-deal, the club sat him down and told him they’d reassessed the risk posed by his heart condition - and it wasn’t one the club was comfortable with, Newsroom reported.
He was, he was told, being released on medical grounds.
An outstanding 2017 provincial season for Southland won him a 2018 contract with the Blues, but his condition prevented him playing for the side.
It has been 13 years since a cardiologist found his heart was twice the size it should have been.
Rheumatic fever, attacks the heart’s valves. A leaking valve meant the heart was not draining blood properly, so it enlarged. Johnson received an aortic valve replacement from a 22-year-old donor who had died in a car accident.
Once he'd returned from Melbourne, Johnson won his way into the Southlands Stags, Northland and the Blues.
Then another red light.
“I then had my annual check-up - and they found there was a leakage again. That was unexpected. I was hoping I would have 15 years from the first [valve]. But it was cut down short to 10.”
The reason was almost certainly the additional workload the demands of professional rugby placed on the valve.
Johnson's fiancée, Sky Sport commentator, presenter and rugby player Taylah Hodson-Tomokino, outlined the path to Johnson being placed in an induced coma.