Tokyo (AFP) - Elin McCready, a transgender woman, has been married for 19 years, but registering her female identity and name has thrown her union into jeopardy because Japan doesn't recognise gay marriage.

"We've effectively broken the system," said McCready, a 45-year-old American, who has three children with her Japanese wife Midori.

"Their options are to say 'Okay, we allow your marriage', in which case they have set a precedent for same-sex marriage, or to say 'No, we don't allow your marriage,' in which case they have to unilaterally cancel our marriage without our consent."

McCready changed her gender marker and name in Texas last year as part of her transition process.

She got a new US passport and had no trouble updating her residency card in Japan, where she is a permanent resident.

But changes to residency cards must be registered with the local government, and when officials there realised that McCready was married, the process ground to a halt.

"They sent it to the Tokyo government, the Tokyo government also didn't want to make a decision and sent it to the national government, and then it's been in committee ever since. More than three months," she said.

A linguistics professor at Tokyo's Aoyama Gakuin University, McCready believes she is the first person to have presented Japanese authorities with this particular dilemma.

Under Japanese law, transgender people can only change their gender markers if they meet certain conditions, including being unmarried, having no minor children, and having no reproductive capacity.

A Supreme Court decision recently upheld those conditions, which can require transgender people to effectively undergo sterilisation in order to change their documents.

But McCready changed her documents abroad and her marriage has long been registered in Japan, so she finds herself in an apparently unique situation.

- 'I have a responsibility -

Her status as a permanent resident means she isn't at risk of deportation if recognition of her marriage changes.

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"I'm in a position to make the challenge... So I feel I have a responsibility to everybody else," she said, as her youngest son Tyler played video games behind her.

Elin and Midori mark their 19th wedding anniversary this month, and have three sons, aged 17, 16 and nine.

They remain close-knit despite the changes to their family unit.

Several years ago, McCready told Midori she wanted to see a gender therapist, and then that she was ready to take hormones.

"It's been complicated, as you can imagine, it has been difficult. But we have found a way to be," McCready says of the couple's relationship.

And the pair say their sons quickly accepted the transition and now correct people who use Elin's former name.

"Fortunately my parents are quite open-minded, and the friends we have are pretty open-minded," said Midori.

- 'We don't want to split up' -

She is insistent that despite the changes in her marriage, her relationship with Elin and their family remains the same.

"For me, Elin is a wonderful parent, a wonderful partner... she's the person I respect most in the world," Midori explained.

"The thing that hasn't changed is the importance of our family to both of us and the fact that neither of us has any desire to go out and form a new family," the 48-year-old added.

Last month a poll in Japan found 78 percent of people aged between 20 and 59 support recognition of gay marriage.

But support drops off among older people, which is significant in Japan's ageing society. And for now there is little sign of legislative change.

In a bid to push the issue forward, 13 same-sex couples filed suits on Valentine's Day accusing the government of discrimination for failing to recognise their unions.

They argue they are being denied rights accorded heterosexual couples and hope courts will declare the government's position unconstitutional.

Contacted by AFP about McCready's case, an official at the Internal Affairs ministry's foreign resident registry would say only that officials are "still discussing the case, making inquiries to relevant ministries."

For now, McCready remains in limbo, unable to act until she gets a decision.

"If they say no, we will resort to legal means," she said.

"We don't want to split up," she said, adding: "Why does the government have the right to split us up?"