From the moment my daughter was born I knew that something was wrong. Call it mother’s instinct. Annie was a beautiful baby, with a sunny disposition, but something about her was not of this world. That’s the best way I can put it – it was as if she didn’t connect with us.

Her brother James was three then and highly intelligent. He was very alert, even as a young baby, and walked at nine months. It seemed unfair to keep comparing Annie with James, so I gave her the benefit of the doubt. At her progress checks, everyone seemed relaxed about her lack of speech. “She’s just a late developer,” they’d say. “She’ll get there!”

I wanted to believe that, so I did nothing. It was only when Annie was three that a very old – and blunt – friend said: “Sophie, for God’s sake, you’ve got to do something about her.” I called in a child psychologist. I didn’t know that with a few simple tests you could see the future.

I sat in the kitchen, willing Annie to succeed as the psychologist gave her three bricks and asked her to build a bridge. She built a tower. At the end of the afternoon, he said simply: “Mrs Dow, you have a problem. Your daughter is mentally handicapped.”

Annie is 17 now and in her final year at a lovely boarding school for “educationally fragile” children in Perthshire. She cannot write or read, but her speech has come along and she’s funny and emotionally intelligent.

We moved from London to Scotland, my husband’s birthplace, after Annie’s diagnosis. The late film director Anthony Minghella bought our house in London. He became a friend and when he created the character of Liv, a Swedish journalist and mother of a child with learning difficulties, in his last movie, Breaking and Entering, I believe he had Annie and me in mind.

For a long time we had no idea what was actually wrong with Annie. Two years of assessment by doctors concluded only that she has “mild brain damage”, which occurred some time during pregnancy. There is nothing mild about it, actually: it is fundamental to her and us. But that was it: once diagnosed, we were kicked into the cold. There was no support system in place to advise us on schools, other than a policy that dictated “inclusion”. I knew that was wrong for Annie, who would be crushed in a mainstream school.

Eventually I read One in Every Class, a book by Christopher Gillberg, a Swedish expert on learning difficulties. Actually, from research I have now carried out, I believe it is more like five in every class who have a learning difficulty, be it a stumbling block such as dyspraxia or something very serious, like Annie has.

Noticing Annie’s physical characteristics – she has long fingers, a slight curvature of the spine and a very long big toe – Christopher suggested she be tested for a chromosomal deficiency commonly known as Catch 22. It was the first suggestion that there might be a genetic reason for Annie’s condition. Dr David FitzPatrick, senior clinical scientist at the MRC human genetics unit at Edinburgh’s Western general hospital, ran the test but the result was negative.

He suggested he keep Annie’s blood sample while he waited for better technology in his lab. Last summer, four years later and totally out of the blue, we received a letter from him telling us that Annie does have a chromosomal abnormality, visible on a high-resolution microscope: 18 genes – out of a total 23,000 – are missing on the short arm of chromosome 1. It is a tiny defect that appears to have had enormous consequences.

Annie is the first person in the world to be identified with this particular chromosomal profile. It is not inherited but occurred as she was developing in the womb. We now have the challenge of identifying all those other “Annies” out there with the same chromosome profile. Doctors can then begin to understand what the 18 missing genes contribute.

Until I had Annie, I wrote about movies. I could never have imagined becoming an expert on the brain. But life throws you unexpected challenges. This week I will be addressing the Scottish parliament on the true extent of learning difficulties, the result of a survey of 30,000 primary schools around Britain. One of the problems is that there is no consensus on what a learning difficulty is, and many have not been diagnosed.

A few years ago I set up Mindroom, a charity dedicated to helping children with learning difficulties. We organise conferences and offer help, support and a forum for parents who need someone to talk to.

This year we ran the first summer camp for children with learning difficulties in Scotland, based on a Swedish model. Next year there will be three more camps. My dream is to create a one-stop diagnostic centre for children with special needs. The first Mindroom centre will bring together facilities for assessment, diagnosis, research, development, education and training. It will cost £10m to build. I have no idea where the money will come from, but I know I will find it somehow.

A year ago I asked three neurosurgeons how much we know about the brain. They said we know about 20% of the brain and understand perhaps 10%. Annie has a mental age of nine so she doesn’t really understand what a huge contribution she has made to this genetic detective story. I hope the next chapter will help us to help thousands of children like her.