Cohen Yau stands just 89cm (35ins) tall – 25cm (10ins) shorter than children his age – and is forced to wear the clothes of a two-year-old.
He was born weighing a healthy 8lbs but refused to feed and medics initially thought he had a digestive problem.
But after mum Kate, 42, successfully bottle-fed him he went home but medics became alarmed when he stopped growing after he reached 18 months old.
Skeletal checks, hormone tests and genetic reports all came back blank and Cohen started school three-and-a-half times shorter than his peers.
In January this year Kate and husband Kevin, 37, an accounts manager, put Cohen on powerful synthetic growth hormones.
They inject him twice a day with Incelux, a largely untested drug that added 2cm to Cohen’s height, but had the side effect of constant nose bleeds.
He has undergone hundreds of tests but doctors have still not been able to fully diagnose Cohen.
Kate, a dance company administrator who also has an eight-year-old son Jet (corr), said: “I have good days and bad days, but we get by.
“It is just so incredibly frustrating because we can’t have any closure. If we know what it is we can move on, whatever the diagnosis.
“But we are left just not knowing.”
Cohen, from Hereford, was born by emergency caesarean section and did not feed for his first 24-hours and so was rushed into special care.
After feeding on a tube for three weeks he was allowed home, but several months later Cohen’s parents realised there was a problem.
Kate said: “They initially put it down to the c-section, and when he continued not to feed they thought it was a digestive problem.
“We eventually got him feeding on soya milk and he came home. But that’s when he started to really lose weight.
“He was being sick quite a lot. And because he was being sick quite a lot he didn’t want to feed and it was like a vicious circle.
“He was still a really small baby, when we were taking him to see our friends. It was noticeable that he was a lot smaller than children of a similar age.
“So that is when we started to think that something wasn’t quite right.”
After a year Cohen had put on two pounds, but had only grown 1cm in height.
After digestive tests came back negative Cohen was referred to specialist endocrinologist Dr Wolfgang Hogler at Birmingham Children’s Hospital.
When a skeletal check came back normal doctors looked to see if he was suffering from a rare genetic disorder, Laron Syndrome, linked to a lack of growth hormones.
But these tests also came back negative. Kate added: “I just burst into tears and my heart sank.
“We were pretty shocked. It not being Laron’s means we have no sure answer what it is and that really affects us, we want to know how to cure what Cohen has got.”
After detailed genetic profiling of Kate and Kevin didn’t provide any answer, they had to make the decision to inject Cohen with growth hormones in January.
Kate said: “He doesn’t like having it, and I don’t like doing it, but we have to.
“He’s very brave. The first few months he got nose bleeds every day, it was horrible.
“The drug isn’t used that much, so we had to make a note to the provider of the nose bleeds so they could log it. Thankfully it stopped after a few months.
“It can also cause a drop in blood sugar levels and a side effect is seizure, but thankfully that hasn’t happened.
“Every year he was growing 1cm a year, but the last year he has grown 2cm – which is an improvement.
“It doesn’t seem to bother him, and he’s got such a great personality he’s very popular at school at the moment.
“But I worry about the future, when kids get older and don’t just take each other how they are, I’m worried he’ll get bullied.
“Even though we don’t have a diagnosis yet we will keep fighting, and I know one day we will get that diagnosis we have been after and we can just move on.”
Kevin added: “Obviously when he goes to school he is going to realise that he is very short compared to the children in his class.
“I do get worried about the bullying. Even like going to the toilet, he knows how to go to the toilet on his own, problem is those toilets at school are a lot bigger or they are non-reachable if you don’t have a stool or someone to help you.”
But Cohen said: “I don’t mind being small, because everyone looks out for me.”
Dr Hogler said: “When I first met Cohen, I recognised immediately there was something not quite right.
“Kids with growth hormone deficiency they are fairly short, but Cohen was shorter.
“Cohen is a puzzle, I immediately thought I had a diagnostic challenge ahead of me.”