Alice Dew had never heard of tuberous sclerosis until it was diagnosed in her son. But the genetic disease had probably been in the family for generations. By David Cohen
"Postman Pat, postman Pat, postman Pat is a very nice chap." Mark Dew, aged seven, keeps perfect pitch as he sings along to his favourite video, his little face right up against the television. Adam, his younger brother, charges around the room with two biscuits in his mouth, flapping his hands and making animal-like noises. He is four years old but he cannot talk. Mark suddenly jumps on Adam's back, Adam screams and Alice, their mother, gently separates them.

Adam settles on the carpet where he manically fills and empties a tub of play buttons. Mark wanders into the kitchen where he stands by the washing machine repetitively slamming the hatch-door. Alice manoeuvres him away, explaining that he is obsessed with the opening and closing of doors and the flicking on and off of lights. Coming out she finds Adam in the loo, just standing there, peering vacantly into the bowl. Then Mark jumps on her lap and strokes her hair. They have a few seconds of intimacy before Adam throws a tantrum. There is hardly a moment when either of them do not pull at her. "People haven't got a clue what I deal with until they spend 10 minutes living with me," she says.

To an observer, Alice's boys may simply appear to have behavioural and hyperactivity problems. In fact, both suffer from tuberous sclerosis (TS), a little-known genetic disorder that affects one in 7,000newborn infants. The term was first coined in 1880 by the French physician Bourneville: when examining the cadavers of people who had suffered mental retardation, learning difficulty and epilepsy, he found tuber-like growths in their brain which were hard, or sclerotic, to the touch: hence the name. It was, however, only with the advent of cranial CT scanning in the Seventies that information about TS began to filter from academic journals into common medical practice.The disorder is by no means rare: although one- third as common as cystic fibrosis and half as common as muscular dystrophy, many health professionals remain ignorant of the condition and it often goes undiagnosed.

Yet early diagnosis is critical: if seizures in small infants go untreated, the higher the risk of severe mental handicap. And although 70 per cent of cases are not inherited but the result of a new mutation, anyone with the disease has a 50 per cent chance of passing it on to their children. At present there is no way of predicting how severely affected a child may be, although boys are significantly more likely to suffer neurological problems than girls.

The symptoms may be mild, but sometimes can be very nasty indeed. They include epilepsy; a characteristic facial rash that looks like acne but does not go away; other skin deformities - rough, white patches on the torso - and learning difficulties. Behavioural problems such as hyperactivity, autism, screaming and excessive rage are common, and benign tumours may occur in the brain, kidneys, heart, eyes, bones, lungs or liver. These tumours may develop without warning in adult life. Constant vigilance is needed because if the tumours cause obstructions, they may lead to serious cardiac or kidney problems.

Alice Dew, 33, who lives in Southport, Merseyside, never knew she had tuberous sclerosis until her brother was diagnosed six years ago. By then she already had one child. Hers is a story of remarkable strength and offers a telling insight of what it is like to live under the shadow of TS.

"My brother, Andrew, who was three years older than me, was born mentally handicapped and epileptic as they called it in those days," she begins. "Mum and Dad owned a small hotel and were very busy, so Andrew followed me wherever I went. It was hard for me to have normal friends because Andrew's behaviour was so challenging - whatever I had, he wanted - and if he had a fit, people were put off. Despite his problems, Andrew was happy. I called him `Smiler' and loved him to bits. I grew up looking after my brother and he looked out for me, too."

With Andrew in the home, studying was impossible and Alice left school at 16 and went to work at Boots. "That was the first time I felt like a person in my own right, just Alice, not somebody's carer or daughter," she recalls. There she met her husband and a few years later she was married.

"I had my first baby in 1987, a little girl called Sarah - unfortunately she was stillborn. We were devastated." It is possible the miscarriage was triggered by the disorder: TS can in some cases cause heart lesions in the developing foetus that result in stillbirth. She fell pregnant again but miscarried at 12 weeks. The third conception was successful and in 1989, she gave birth to Mark. "I couldn't believe when he came out alive. I was ecstatic," she says. And for a while she was happy. She knew nothing of tuberous sclerosis and apart from being severely long- sighted and needing glasses at six months, Mark seemed "the most normal child in the world".

But when Mark was 18 months, Andrew underwent a brain scan for his fits which had become severe. It was only then he was diagnosed as having tuberous sclerosis. "My mum said, `He's got what?' None of us had heard of the condition. The specialist replied: `Yes, tuberous sclerosis and you have it, too.' He could see from the pockmarks on her face. It is amazing how Andrew got to nearly 30 years old without diagnosis, yet so many of the tell-tale signs - skin patches, epilepsy, learning problems, facial rash - were there. The whole family had to be tested. What a shock. The scan showed that I had it and Mark, too."

At first it didn't sink in. Alice knew that, apart from a rash on her back, she had none of the symptoms and from what she could see, Mark's physical development seemed normal, so she thought they were "the lucky, mildly-affected ones". After taking genetic counselling and seeking advice from the Tuberous Sclerosis Association - a body established in 1977 to provide education and support for carers - she and her husband decided to risk another pregnancy. "We were told there was no way of detecting in utero whether the foetus had TS or not. It was a gamble, but I just didn't want Mark to be an only child."

Medical research has advanced since then. According to Dr John Osborne, a consultant paediatrician at the Royal United Hospital in Bath who runs one of only three TS clinics in the country (the other two being in Leeds and Cambridge), TS can now be detected in utero in certain rare cases. "We have isolated the sites of the two rogue genes that are responsible for TS. The first is on chromosome 9 and the second on chromosome 16. We think that about half the people who have TS have damage on chromosome 9 and the other half on chromosome 16. Although the gene on chromosome 9 has proved difficult to isolate, researchers have cloned the gene on chromosome 16 and have found that it produces a protein called tuberin which seems crucial to controlling cell growth all over the body and whose absence causes TS. For those parents who are known to have the chromosome 16 variety of TS, ante-natal scans may detect if there has been a huge deletion of the gene on chromosome 16. And if the detection is early enough, a decision could be made to terminate."

Alice duly gave birth to Adam and for 12 months it seemed the gods had smiled on her: the new baby seemed perfectly healthy. But the following year both her sons began having epileptic fits. That was just the beginning. Within short order, her brother who was having continuous fits, died after brain surgery and her husband announced, after 10 years of marriage, that he had been having an affair for four months. He walked out and left her to bring up her two sons on her own. She refuses to speculate on whether the strain of coping with the disease had broken up the marriage. "I was utterly devastated, not just by the affair but by the fact that he did it while I was visiting my dying brother in hospital." They are since divorced.

Today, Mark attends a special school for children with moderate learning difficulties, while Adam has just started at a nursery school for children with severe learning difficulties. Both her sons look physically normal, but may have up to four epileptic fits a week and display acute behavioural problems, although Adam's mental impairment appears far worse than Mark's.

"Adam is autistic and gets very frustrated and so do I," admits Alice. "Some people sail through life while others, like me, seem to have more than their fair share of problems. For seven years I've put my sons first, second and third.

"I wouldn't swap my children's personalities for the world. I wouldn't want to be without them. But I find it hard to see who I am beyond their carer."

The Tuberous Sclerosis Association can be contacted on 0115-923-4301.