EVERY time there is a knock at the door or the phone rings, Mark freezes.

The dad-of-three fears it will be the news he most dreads – that he will never see his ‘caring and selfless’ little sister Isobel Munro again.

On Monday, April 11, the family were plunged into sadness when Isobel, who has learning difficulties and is profoundly deaf, disappeared without trace.

Despite fearing the worst, Mark cannot stop himself imagining that 'Isi' is still alive and has launched an emotional appeal for information.

It comes as police renew their efforts to find out what happened as Isobel has turned 42.

Mark, said: “My sister has been missing for over five months. It is desperately sad that on her birthday we do not know where she is or how she is.

“We can only cling onto a shattered hope that she is still with us and is able to acknowledge a day that would normally be one of celebration.”

Isobel, who wears a hearing aid and lip reads, was last seen by her mother on Monday, April 11 when she left her home in Latimers Close, Christchurch, in a taxi.

Police said she was dropped off at the car park next to The Globe pub on Lymington Road.

However police say there have been no sightings of her since.

Isobel lived with and cared for her mum Lesley, who has health problems.

She was reported missing the following Monday.

On Sunday, May 15, as a result of ongoing investigations, police officers were joined by volunteers from Dorset Search and Rescue to search a wooded area between The Globe pub and Chewton Common Road however nothing was found.

Mark, who lives in Dublin and works in financial services, said: “It’s been very distressing especially as there seems to be no trace of her anywhere.

“Isobel would go into town to do the shopping, pay the bills, pick up prescriptions and go to the post office.

“She said goodbye to my mother, got into a taxi and left, but this time, she never came back.

“She hasn’t used her phone and she hasn’t used her bank account.

“There has to have been some sort of sighting or some information.”

Mark, 45, said Isobel has gone missing in the past and has travelled through the country on public transport but had always returned.

He said: “It has been extremely difficult, to feel haunted every day is a good description. I’m worried sick. The police have been brilliant but the torment of not knowing where or how Isobel is, is always there.

“It never leaves your mind.

“You have to prepare yourself to hear the worst. You constantly expect a phone call or a knock on the door to come. It is horrendous not knowing. When it’s cold or wet out, I can’t help but think about where she may be and if she is safe."

Isobel is described as white, 5ft 6in and of medium build. She wears glasses and has mousey brown curly hair in the style of a bob.

Mark, said: “I visit the area every month and I’ve discovered Isi was very much loved.

“Isi is someone who only wants to please. She would come across to all those she had dealings with as friendly and caring and selfless. She got on with life despite the hurdles that she constantly faced.

“I have very fond memories of holidays abroad as children. My dad, who passed away aged 53 from leukaemia, had a yacht in Poole Harbour and we’d go across the channel. I moved to London for work and now my life is in Dublin. Despite her difficulties, Isi was able and very happy.

“She gave, especially to her mum, without question.

“But it seems life hasn’t returned any of what she gave. Hopefully there is still time for that.

“Isi, we love you and we miss you more than you know. If you see this, please make contact in any way you can to let us know you are okay. If you are worried about anything, I want you to know I understand and that things are different now. You haven’t upset anybody.”

Anyone with information should visit dorset.police.uk or call 101, quoting occurrence number 55160060585. Alternatively contact Crimestoppers anonymously on 0800 555111.