Bonnie was born in September 1996, a normal, healthy baby girl. Then, at six weeks, she was given antibiotics for bronchiolitis and changed from a calm baby to a fretful one with persistent diarrhoea. From six months to a year old, she had a series of ear infections and more antibiotics. These seemed to upset her gut and she became even more fretful and clingy. Aged one, she had met all her physical milestones and was using language appropriately, but had started doing things such as obsessively picking up gum from the pavement. She resisted all food except bread and milk products. At about 18 months, I noticed further obsessive behaviour: she would line things up, and was fixated on the video of 101 Dalmatians. Because she wasn't really healthy, I decided she shouldn't have the MMR vaccination at this point Our GP agreed. But by 22 months, she seemed as fit as she could be - although she still had diarrhoea - so I went for it.

You could see the effect on Bonnie immediately. She was awake every night from 1 am to Sam, with wide eyes and dilated pupils. At breakfast she would babble frenetically, run up and down, stick her fist into the bread and stuff it in her face. Within two weeks, her skin became almost translucent. She virtually stopped talking. About two months after the jab, she developed a compulsion for milk, and became incredibly anxious.

By now, I knew she was deeply sick. But it took more than four months for a paediatrician to say it was 'probably' autism. For a firm diagnosis, Bonnie would have to be assessed by a multidisciplinary panel, which would take another six months.

In frustration, I contacted Paul Shattock, of the Autism Research Unit at the University of Sunderland, who is conducting research into autistic children with an intolerance to gluten and casein the proteins in bread and milk. I sent him a urine sample from Bonnie, which tested positive. He explained that problems can start when the balance of good and bad gut bacteria is disturbed, which sometimes happens following repeated courses of antibiotics, and can lead to chemicals forming that cause teaks in the gut wall. Peptides, the product of the gluten and casein proteins, leak into the bloodstream and up to the brain in greater quantities than usual. Behavioural problems arise because the peptides are opioids similar to morphine and heroin.

Why the MMR vaccination seemed to propel Bonnie into such total disengagement is not cear, but because it delivers live particles of the measles virus (which have been found in the guts of autistic children), it may exacerbate existing problems in children with a vulnerable immune system.

I was told to remove gluten, then casein, from Bonnie's diet. After two weeks, she slept through the night, her diarrhoea stopped and the colour in her cheeks returned. The most extreme aspects of her behaviour improved, but Bonnie still had impairments in communication, language and imagination and, somewhat ironically, it was now that she was formally diagnosed as autistic. Further tests showed that at two years and nine months her developmental age was just 15 months. So she started an intensive one-on-one educational therapy called Applied Behaviour Analysis (ABA) for 40 hours a week. In six months she had caught up a year.

When Bonnie was four, Dr Michael Tettenbom of Frimley Children's Centre in Surrey recommended cutting out sugar and yeast from her diet and taking a course of nystatin (anti-fungals) to balance the gut flora and reduce her bloated tummy. We also added probiotics and fish oil supplements which she still takes. The bloating went down and her alertness increased.

Bonnie is eight now, in mainstream school, popular and affectionate. She knows some foods were making her sick and totally accepts that she has to stay on her special diet.