Ethan is missing an exon on a gene called dystrophin, a protein in the muscles. It's the biggest gene in the body and contains 79 exons. He is missing number 51.
If Oliver's condition is confirmed, it means both boys will develop weakening muscles, problems with motor skills such as running and jumping, have frequent falls and trouble climbing stairs.
The weakness progresses quickly and breathing and heart disease usually start by age 20, leading to heart failure.
The defective gene is believed to have been passed down by Mrs King, who had no idea she was a carrier and said there was no history of the condition in her family.
She and her husband, a builder, were shattered when both their sons tested positive. Until then, the Mt Wellington couple's elder boy had been relatively normal except that he was slower at reaching physical milestones than his peers.
"He didn't crawl until he was nearly 1 and didn't walk till he was 17 months," Mrs King said. "When he did start walking, he was quite unstable, and he still falls a lot."
Mrs King, 34, a former high school geography teacher, said that when there had been no improvement after a year of visits to a chiropractor, she knew things weren't right.
It took four months for a referral to a paediatrician, who immediately tested Ethan for muscular dystrophy.
"He rang me on the day of the test and I knew, as soon as he rang me, that it was something bad.
"It's hard to believe. I always knew something was not right but I never expected the severity of it."
Ethan will start a steroid soon to slow the loss of muscle strength but the drug has side-effects and only one, prednisone, is funded in NZ.
Money raised from the family's Givealittle page, which is at more than $8000, will go towards future treatment and a purpose-built home with wheelchair access that the couple hope to build north of Auckland to be closer to Mrs King's parents.
Starship paediatric neurologist Dr Rakesh Patel said treatment for DMD was more advanced now and some children were living into their 30s and 40s, albeit severely disabled.
However, he said, there were at least four research projects under way overseas, one of which Kiwi kids were participating in, aimed at minimising the effects of the disease.
Dr Patel said any future treatments would be expensive and so far steroids were the most effective drug.
If you want to help the King family, visit givealittle.co.nz
Duchenne Muscular Dystrophy: Q&A
What is Duchenne Muscular Dystrophy?
The most severe kind of muscular dystrophy, DMD aggressively weakens the muscles.
What are the symptoms?
Symptoms usually appear before age 6 and may surface as early as infancy. They may include fatigue, learning difficulties, intellectual disability and muscle weakness. Children can become wheelchair bound by about age 12.
What are the treatment options?
There is no cure for DMD but treatment is now more advanced. Steroids, including one in development, have increased life expectancy by several years, increasing the length of time a child can walk, and preventing spinal surgery by stopping a child's spine curving and compressing the lungs.
Can girls be born with it?
Because of the way the disease is inherited, it usually affects boys.
What research is being done worldwide into this disease?
There are several projects and trials including one in Australia called exon skipping. This drug plasters over the genetic error or damaged exon, to allow the body to read the protein. The trial is showing good results in children, which enables them to walk for longer.
Sources: Dr Rakesh Patel of Starship Hospital, and Medline Plus website
