Jonathan's condition "has stabilised despite doctors' predictions"

Jonathan Simms, 18, from the west of the city, was given repeated infusions of the drug pentosan polysulphate directly into his brain.

The drug has not yet been tested on humans and the Simms family took an NHS trust to court earlier this year to get the treatment approved.

Don Simms said his son's condition has stabilised despite what was originally predicted by doctors.

"These are small but significant changes," he said.

We are not hailing it as a total success but from what we have seen so far we are much encouraged Don Simms CJD patient's father

"What I can categorically state is that Jonathan has not got any worse, he in actual fact shows signs of improvement.

"We have never claimed that the drug is a wonder cure, we simply do not know.

"This is why we as family have to be guarded in our optimism. We are not hailing it as a total success but from what we have seen so far we are much encouraged."

While laboratory experiments suggest the drug has the potential to tackle the condition, the drug is controversial because it has only received limited testing in animals.

Last January, a tube was inserted into Jonathan's brain to allow a total of 12 infusions, with gradually increasing doses, be given.

However, fears remain that the treatment may cause harm.

Jonathan's progress is being monitored using regular scans checking for the presence of bleeding around the injection site.

Jonathan requires round-the-clock care

The teenager's condition has deteriorated in the months that his father has been campaigning for him to have the treatment.

He now requires round-the-clock care and the disease has severely affected his speech and eyesight.

More than 100 people in the UK are known to have died from the variant form of CJD so far, with a handful now living with the illness.