West Australian couple Leon and Danielle Green's heartbreak after losing little Airlie - two years after the death of their baby boy Sonny to the same rare condition: 'We're broken'

A couple say they are 'broken' after they lost a second child to PPA2, a rare genetic condition that mainly affects the heart and can cause sudden cardiac arrest.

West Australian couple Leon and Danielle Green's 18-month-old daughter Airlie died four weeks ago, two years after the death of their nine-month-old boy Sonny. 

At the time of Sonny's death, though, the couple, who live in Baldivis, 46km south of Perth, did not know what had caused it. 

It was only when Airlie suffered from ventricular fibrillation - which causes rapid, inadequate heartbeat - at five months that a geneticist realised what was wrong.

The discovery of the rare genetic mutation gave them an answer for what happened to Sonny and hope for their daughter's care. 

'She was a happy, healthy girl until she got sick, and she got through multiple viruses. We were very positive about how her journey was going,' Mr Green told Yahoo News. 

Airlie's condition was 'quite complex' and required 'a very strict medical emergency plan' for whenever she was ill. 

'We started a support group online and found bunches of other families across the world going through a similar crisis. The group was growing. 

'We just dedicated our life to getting answers and how to best manage her when she was unwell,' he said.

But earlier this month, Airlie got a bad case of gastro, which brought on a  cardiac episode and her parents took her to a hospital. 

The toddler was given the all-clear and sent home 24 hours later.

However, two days later, on May 4, the Greens rushed Airlie back to hospital as she was vomiting so much.

'That's when everything just went downhill,' Mr Green said. 'It was an extremely traumatic day and unfortunately we lost her.'

Airlie's blood pressure dropped, which raised her heart rate and she went into cardiac arrest.

The Greens have been unable to return to work in 'fear of facing everyone'.

'We're broken ... We're going through all of the real rough stuff that we have to do,' Mr Green said.

His brother Patrick has launched a GoFundMe to help allow the couple 'time off work to heal' and to help with funeral expenses, with any extra funds being donated to the Starlight and the Heart Kids foundations.

Mr Green said if they had known what caused Sonny's death before Danielle fell pregnant with Airlie, they would have instead considered using IVF, which can detect the gene early. 

Having gone through the unimaginable pain of losing two children, the Greens want to educate people about PPA2 'and potentially help the next family that has to face that'.

They would like to see standardised genetic testing for expectant parents in Australia, which could help detect 'gene code errors' at an earlier stage. 

This could help save other families from going through what they have.