Little Benjamin Davey was born on November 2013 weighing 6Ibs 9oz at the Royal Infirmary of Edinburgh.
But the youngster, who is visually impaired, is one of 6,000 children born in the UK every year with a syndrome without a name (SWAN).
When his mum Alex, 40, was 38 weeks pregnant she was told Benjamin’s brain was underdeveloped and he would have a low chance of surviving the birth.
Alex, from Dunbar, East Lothian, was offered a termination because the five-year-old’s condition was so severe but Alex felt she had to give him “a chance”.
And now, Benjamin has grown up to become a “lovely boy” despite the family not knowing what type of care he should be receiving due to him having no diagnoses.
Alex said: “My first few scans when I was pregnant were normal.
“But when he got an MRI scan while I was pregnant it revealed that his brain wasn’t developed.
“Doctors offered us a termination but we wanted to give him a chance because we couldn’t make that kind of decision without knowing what was actually wrong with him.
“Since he’s been born we just try and get on with it.
“But the most difficult thing is the long term planning because we don’t know if his condition will change as he gets older.
“We don’t know if he will need a carer or anything like that.
“Even explaining to people what he suffers from is so difficult because not everyone knows that you can get undiagnosed conditions, which is frustrating.
“We don’t know how long he will live so just have to get on with it and try and make memories for him.
For the first 18 months, Benjamin was breastfed but due to an epileptic seizure during that time he has since been tube fed by Alex and her husband Richard, 38.
Benjamin will be in a wheelchair for the rest of his life, said mum Alex.
Alex said it is difficult to communicate with Benjamin because he is also visually impaired and can’t speak.
The mum-of-three, who works as a botanist, added: “It can be really hard for us as he has a range of symptoms.
“He has epilepsy and something called dystonia which means his muscles spasm.
“He also has something called global developmental delay which means he doesn’t develop like a normal child.
“But he’s a lovely boy who is really happy.
“He doesn’t know any different, so he can only show what he feels through his body language.
“And although he is visually impaired he likes watching lights and shadows.”
SWAN is used to describe a person who is believed to have a genetic condition but the exact cause cannot be found.
It is thought to affect around 6,000 babies a year in the UK, half of which will never receive a diagnosis.
SWAN UK national coordinator, Lauren Roberts, said: “Life for families affected by undiagnosed genetics conditions is tough, living in limbo land with no answers they often feel like they have nowhere to turn.
“Undiagnosed Children’s Day is a chance for them to come together to raise awareness of the issues they face and celebrate all that their children achieve.”