Living with Ma and Da until your 30s is common in a recession - but in Japan, with the lowest birth rate in the world, the increase in 'parasite singles' has turned into a serious social problem. Some extremely withdrawn teens can end up spending more than 30 years in their bedroom. David McNeill reports

There are only two lasting bequests we can hope to give our children, said American writer Hodding Carter. One of these is roots, the other, wings. But what if children plant roots so deep they don't sprout wings until their 30s, 40s or even beyond? That's the dilemma facing millions of Japanese families stuck with older children who won't leave the family nest for school, work or marriage.

Grown-up kids refusing or unable to leave home is, of course, hardly unique to Japan. A decade of skyrocketing house prices has also left many Irish twenty-somethings stuck living with Ma and Da, and only half all Irishmen and slightly fewer women now leave home by 26. But the Japanese problem is deeper and, at its worst, can involve grown children completely withdrawing from society and sponging off parents until they die.

Not everybody, though, is unhappy with what Japan calls its "parasite singles". Take the makers of luxury brands. The Japanese economy is in its worst postwar slump, with bankruptcies, unemployment and government debt all running at record highs. Yet sales of Louis Vuitton in Japan have grown 20-fold in the 1990s and now account for one-third of the company's worldwide market. The firm broke its sales record for single-day sales, shifting more than €1 million worth of goods, when it opened the world's largest outlet in Tokyo in September 2001.

Nor was this a one-off. Gucci has opened seven Japanese stores since 1998, Hermes established an 11-storey outlet in Tokyo last year, the Italian jewellery firm Bulgari attracted a queue of hundreds when it opened its remodelled flagship store in the city last month, and Dior and Prada are also getting ready to set up shop. In the world of luxury-brand goods, Japan seems to be recession-proof.

The reason can be found by taking a stroll through the fashionable Ginza district, Tokyo's glitzier version of Grafton Street, where many of these iconographic names blow neon raspberries at the country's fourth recession in a decade. As staff in many of these shops will tell you, their best customers are single women in their 20s and 30s, many of whom still live at home with mom and dad.

According to sociologist Masahiro Yamada, who coined the term "parasite single", 80 per cent of single Japanese working women aged 20 to 29 still live at home, with the figure for unmarried men in their early 30s standing at 50 per cent. Yamada claims there are about 10 million parasite singles of both sexes in the country.

Thirty-six-year-old Norie Koganei, for example, earns about €1,700 a month as an accounting clerk for a translation company. She pays nothing toward the house because she says her parents "want me to save for the future". Norie drives a car, carries the obligatory Louis Vuitton handbag and, during what they call Japan's "lost decade", has been to Canada, Spain, Italy, Britain, Hong Kong and Hawaii. "I'll move out when I get married," she says.

Although travel firms, restaurants and the makers of minicars, mobile phones and expensive handbags are delighted to have millions of Nories out there, Yamada is not and can regularly be found in print bemoaning the long-term effects of the parasite phenomenon on society. For one thing, he says, it's one reason more than half of Japanese women are now postponing marriage until after their 30s, helping to explain the country's plummeting birth rate, which, at 1.34 children per woman (compared to about 1.9 for Ireland), is the lowest in the world.

The fertility rates are so low that the government has alarmingly warned that the Japanese are on their way out in less than 100 years, unless some way can be found to persuade women to have babies, which is why it has recently boosted annual children's allowances to about €2,400.

Such talk naturally angers Japan's feminists, who argue that the parasites are a symptom rather than a cause of declining marriage rates and fertility. The problem they say has much more to do with a sexist status quo that expects women to give up work after marriage and play second fiddle to workaholic husbands.

Some commentators indeed are delighted with the development. "Politicians now have to beg women to have babies," feminist journalist Mitsuko Shimomura told the New York Times recently. "Unless they create a society where women feel comfortable having children and working, Japan will be destroyed." The carefree and shallow parasite is sometimes the butt of jokes on Japanese television but no one is laughing at its most extreme manifestation, hikikomori, which is slowly being recognized as a genuine mental disorder. Roughly meaning social withdrawal, hikikomori refers to children who initially refuse to go to school, then work and finally end up living hermit-like existences in the family home.

"My worst case is a 45-year-old man who has been holed up in his room for 30 years," says Dr Tamaki Saito, a psychiatrist who has written a bestselling book about the problem.

"His parents hardly ever see him even though he lives in the same house, because he gets up at midnight to eat and read and goes back to sleep before his parents are up." Dr Saito, who estimates there could be as many as one million hikikomori in Japan, runs the only clinic in the country that treats the disorder.

"The government only started to notice the problem a few years ago when there was a spate of crimes involving children and their parents." The most notorious was a man who kept a young girl captive in his room for nine years under the nose of his mother. "I knew there was something going on but I was afraid to go into his room," the mother later told an astonished Japan.

But why don't the parents just kick their kids out? Dr Saito laughs. "That method might work when the sufferers are young, but as they get older it can become dangerous because they can turn violent. In the West, adult children living with mom and dad are considered weird. You're expected to move out and set up home on your own. But here there is a tradition of living with parents, who feel responsible and embarrassed about discussing the problem with strangers, so they keep it hidden."

The problem is compounded, says Saito, by the lack of serious mental health care or support services in Japan. Most hikikomori problems develop in mid-teens, when the pressure from Japan's exam-driven education system, with its strict discipline and top-down teaching methods, begins to ratchet up and young noses are pressed ever closer to the grindstone.

Some alienated teens react by locking themselves in their rooms and refusing to go to school, and a good parental clip around the ear often has the opposite of the intended effect.

"My mother hit me every day for weeks," says Kanako Mizoguchi, who woke up one day at 14 and decided she'd had enough. "It just made me angrier because she never asked me how I felt. It was the same in school." Kanako spent five years sleeping 12 hours a day and "retreating into a world of books. My favorite was One Hundred Years of Solitude, by Gabriel García Marquez." Visits from her few friends trailed off as they graduated and started working.

Now 19, with a sharp and witty personality hiding behind a sullen distrust of anyone over 25, she was rescued by a unique support centre that tries to treat the victims of social withdrawal while they're still young. Run by Satsusugu Kudo, the Youth Independence Support Centre has been operating for almost 30 years on funding from parents and benefactors. "We don't get a yen from the government," he says.

Around the ramshackle centre, shy young men and women scurry out of sight like night creatures exposed to the sun. Requests for photographs are turned down until it is explained at lunch that they will be published in an Irish newspaper and not in Japan. Reluctantly, some agree while others leave the table or hide their faces. Still, the fact that these youngsters are here at all and not holed up in their rooms is progress.

"We can cure it if the kids come to us young, but once they reach their 30s or 40s, it's really difficult," says Kudo, who believes the hikikomori issue is part social and part cultural. "It's worsened as Japan has got richer and the old sense of community has broken down, pushing people into their own boxes. The education system doesn't help, because it doesn't allow people to develop. And the problem just grew and grew for years but people hid it at home until they couldn't do so any more."

Kanako says she is confident she will get better. "I can talk things out here with others, so I no longer feel like I'm invisible. That was the problem before.

"I felt like I was being erased. It was a terrible feeling."