Had it stopped at an appropriate point, the story of Patrick Stuebing and Susan Karolewski could have been poignant and moving.

Separated by adoption in their native East Germany, the siblings met for the first time in 2000 when Patrick tracked down his birth mother and the younger sister he had never met.

If their mother, Ana Marie, were alive today, however, she would, in all likelihood, be wishing her estranged son had never found his way home.

Because for the past seven years, brother and sister have been lovers. In that time they have had four children together - two of whom are mentally and physically disabled and all of whom are now in care.

And despite the fact that 29-year-old Stuebing, an unemployed locksmith, has already served two jail sentences for committing incest with his sister, now aged 22, the couple defiantly refuse to give each other up.

The disturbing story of their twisted relationship emerged this week as the pair announced plans to take their case to Germany's highest legal body, the Constitutional Court, in a bid to legalise their shocking union.

Astonishingly, they are doing so despite the fact that two of their children can barely walk or talk. Experts believe that such birth defects are caused by inbreeding.

But in a case that could have ramifications across Europe, and which has been presented by liberal sympathisers as a romantic battle against oppression, the pair argue that they are being denied the right to sexual freedom.

"We do not feel guilty about what has happened between us," they announced in a statement. "We want the law which makes incest a crime to be abolished."

To most people, this would seem to be an open and shut case. And yet, because Germany's laws on incest were introduced by the Nazis, they are an easy target for Left-wing groups who can conveniently argue that they are nothing more than an extension of the Third Reich's Aryan racial hygiene laws.

Such groups argue that the laws should be overturned in favour of freedom of choice and sexual determination. Or, as the couple's lawyer, Endrik Wilhelm, puts it: "Everyone should be able to do what he wants as long as it doesn't harm others."

But many say the practice of incest does harm others. Children born as a result of incest are at an increased risk of developing severe mental and physical disabilities. Incest laws are seen as a deterrent and help prevent children being born with the disabilities that result from genetic defects and inbreeding.

Back in Germany, the story has provoked moral and scientific outrage.

"When siblings have a child together, there is only a 50 per cent chance that it will be healthy when it is born," Jurgen Kunze, professor of human genetics at Berlin's Charite hospital, told one newspaper.

German newspapers mockingly call them the "forbidden lovers of the Fatherland" but, clutching each other on the sofa at their home in the small village of Grossdalzig near Leipzig, the pair insist they couldn't help themselves.

"We didn't know each other in childhood," says Susan. "It's not the same for us. We fell in love as adults and our love is real. There is nothing we could do about it. We were both attracted to each other and then nature took over from us. It was that simple. What else could we do? We followed our instincts and our hearts."

In fact, as the Mail has discovered, the details of the relationship make uncomfortable reading. Stuebing was the third of eight children born into a poor, uneducated, dysfunctional family. His violent father, now dead, attacked him with a knife when he was three and he was made a ward of court and then adopted. Susan was born into the same unhappy family - on the same day her parents' divorce was finalised.

Her childhood was unspeakably deprived. Her chain-smoking, unemployed mother often left her at home alone, or entertained lovers while she was there. Poorly educated and barely able to write, even today, Susan remembers being unloved and a burden to her mother.

Six other brothers and sisters, some of whom were born with disabilities, died in childhood. One was run over and killed age seven.

Another mentally handicapped sister died age eight. Susan was close to one of her disabled brothers, Andre, but he died in the same year as her mother.

When Stuebing was 18 he decided to find his biological parents. Four years later he tracked down his mother and discovered Susan. He moved in, and, astonishingly, Ana Marie allowed him to share her young daughter's bedroom.

"We both stayed up late into the night to talk to each other about our hopes and dreams," he says.

Six months later, Ana Marie died of a heart attack. Susan was relying more and more on her brother. It is not hard to see how she might have confused such dependency on her brother with love as she struggled to cope without her mother.

In her own words: "Trust grew into a different type of love when our mother died six months later."

Taking into account her lack of education, it is perhaps not surprising. She left school at 15 with no formal qualifications. A reporter who visited her at her home spoke of her obsessive nail biting and the simple way in which she spoke.

The bond appeared to develop out of dependency on Susan's part and perhaps a need to be respected and in charge on Stuebing's.

He says: "I became head of the family and I had to protect my sister. She is very sensitive but we helped each other during this very difficult period and eventually that relationship became physical."

Despite already having experienced a normal relationship with a woman, he insists: "We didn't even know we were doing anything wrong when we started sleeping together. We didn't think about using a condom. We didn't know it was illegal to sleep together.

"Our mother would not have approved, but the only ones who should judge us now is us."

In October 2001, aged just 16, Susan gave birth to a baby boy, Erik. He was taken into care and now - aged five and living with foster parents in Potsdam - can hardly walk or speak properly.

Sarah, now four, was born in 2003 and suffers similar disabilities. She was also taken into care, as was Nancy, nearly three, who appears to be normal. Sophia, now two, was born while Stuebing was in prison.

Under the care of German social services, Susan tried to hide the pregnancy by wearing baggy clothes. She gave birth alone in the bath. Stuebing has since been sterilised in the mistaken belief that if he has no more children with his sister, he will evade jail. And yet both are apparently in denial about their children's disabilities, despite expert opinion.

"Two of our children are disabled," says Stuebing. "But that is not necessarily anything to do with the fact that we are siblings. There are other disabled people in our family. We had six brothers and sisters who did not survive in some cases because they were disabled."

The pair were tried for incest in 2002. The district court in Leipzig heard how from January 2001 until August 2001, Stuebing "had sexual intercourse with his sister 16 times. Only at the beginning did the accused bother using condoms".

Stuebing received a year's suspended jail term after being found guilty on all counts. Susan, then 17, was treated as a juvenile and placed into the care of youth services.

But after the birth of two more children, the court was not so lenient. Stuebing was eventually sentenced to ten months in prison.

They found themselves in court again in 2005 on account of their other daughters and Stuebing was sentenced to two and a half years for re-committing incest.

When he was taken to jail, a tearful Susan told German newspapers she could not live without him. Stuebing threatened to commit suicide. Yet while the brother was locked up, the sister conceived a fifth child by another man.

Even so, upon Stuebing's release, she gushed to German reporters: "I'm so happy Patrick is here and that I have him again. I need him."

Stuebing in turn told the cameras: "I am doing well. I will always be there for Susan and the children."

They have been living together, but he has one year and five months of his sentence still open, and as he is openly back with his sister, he will be jailed again and again unless he can overturn German law.

"We are challenging this law because we do not want to be separated ever again," he says from the two-bedroom council flat where they live with Susan's latest child and a dog called Tyson.

Incredibly, the couple even argue that they might not have had so many children if the first hadn't been taken away. Stuebing says: "The younger children might not have been born had they not taken the first one from us. We just want to make sure that we don't lose everything again."

He and his sister visit their son Erik in care. He adds: "When you see your child being looked after by someone else when they should be with you, that's hard for any parent to bear. So if he is handicapped, well, that is all the more reason we should be able to look after him."

They also talk about wanting their oldest daughter Sarah back with them, but are happy for the others to remain with foster parents. "It would all be too much and we do not have enough room," says Susan, adding with unwitting irony. "We want to do what is best for them."

It is clear she is still utterly dependent on her brother. At home, she likes to read teenage magazines and watch Germany's version of Big Brother.

"When I go to the shops in the village, all the little boys call me rude names," she says. "But I can bear it all as long as Patrick is with me."

Stuebing admits he underwent a vasectomy in the hope it would mean he could live with his sister without fear of further prosecution.

"There is no reason for them to jail me now," he says. "I do not want to go back to jail and I know we will never voluntarily leave each other. If anyone doubts our love they should just see we will not be kept apart."

Few people would see this as a compelling argument to keep him out of prison. But while incest is one of the few remaining sexual taboos, in legal terms, at least, Europe remains divided. France's incest laws were abolished in 1810 by Napoleon. It is also not illegal in the Netherlands, Belgium, Luxembourg, Portugal or Turkey.

But in Britain, incest remains forbidden. The law was extended in 2002 to cover not just blood relatives but also step parents and children and cases of adoption.

If ever there was an argument for retaining incest laws, the story of Patrick Stuebing and his sister Susan Karolewski is surely it.

It is almost inevitable that when Germany's highest court decides on this case in around six weeks time, it will uphold its incest laws and send Stuebing back to jail.

It is a prospect Susan is distraught about. "We want our children back to raise them as a proper family," she says. "We love each other," she adds naively. "Surely that is all that matters?"

In the end, of course, the unfortunate children who have resulted from this twisted union matter far more. Whatever happens, they will have to live with the stigma of their parentage for the rest of their lives.

i'm not gonna lie, i didn't read the whole thing but i do like to say that marriage and/or sex between relatives shouldn't be illegal, that's their thing, it's none of by business. is it disgusting? yes. the only thing i really have an issue with is when they consciously (which really is debatable in the first place since they're fucking each other) decide to have children.

It should be illegal just because of the possibilty of the type of birth defects described in the article. Two of their kids cannot walk or talk. If these two want to stay together, they should both be sterilized. What a fucked up world.

We can`t judge them from what they feeling, called "love", "sex",..anyway,..that`s not the point. This guys are so irresponsable in the way they were not use protection. Why she doesn`t take a pill, or he used a condom,..........
And now this coming kids maybe will born with some problems or defect,....this is sad, everyday we are all more crazy and stupid,..too bad.

It should be illegal just because of the possibilty of the type of birth defects described in the article. Two of their kids cannot walk or talk. If these two want to stay together, they should both be sterilized. What a fucked up world.

I'm no geneticist, but if both parents are normal, and don't carry genes for such defects, why is there any more chance that such defects would arise than between two unrelated parents?

Seems like a myth to me. Where's that thread about marrying cousins?

my wife works for an organization that helps out poor families with disabled children. there's one family, they're from Morocco, where the parents are first cousins, they had 3 kids, all heavily retarded.

Because of the genetic implications, you must introduce new genes to your gene pool.
Continued procreation with a limited number of genes then promotes more severe birth defects due to the lack of the genes capacity to mutate in a manner in which is benifical, because you're forcing mulitiple couplings of genes to becoming in contact with like genes.

Please explain why this requires government legislation.

uh-huh. Nice anecdote.

Marrying first cousins is commonplace in the Arab world. Not all of them are retarded, although it may explain some things.

Regardless, fucking your sister doesn't CAUSE genetic mutations, so either they are there to become evident, or they are not.

uh-huh. Nice anecdote.

Marrying first cousins is commonplace in the Arab world. Not all of them are retarded, although it may explain some things.

Regardless, fucking your sister doesn't CAUSE genetic mutations, so either they are there to become evident, or they are not.

Explain why interracial couples have a tendency to produce gorgeous children?

Game over.

Hey, man, I'm a big proponent of this idea. It's why Tiger Woods is superhuman. I believe that the cream rises to the top and that the more variation and diversity in a gene pool, the more likely the better genes will survive and propogate and the lesser ones will fall away.