Just over eight years ago, we were blessed with the arrival of our first child, Sophia, who was born healthy and full of life.

Like all babies she had the standard newborn heel prick test to check for signs of rare disorders and illnesses. While I wept like a baby, thinking about my little girl being prodded, she hardly even flinched and then it was over.

Three days after bringing Sophia home, I got a phone call from a number I did not know that would change our lives forever. On the other end of the phone was a nurse from the Royal Children’s Hospital in Melbourne who told me that the results of Sophia’s heel prick test were irregular, and would require further testing.

The very next morning, we returned to the hospital where further tests confirmed that our baby girl had Phenylketonuria (PKU), an incurable and potentially debilitating rare disease that I had never heard of.

While Sophia’s diagnosis is rare, PKU in fact impacts one in every 15,000 babies born in Australia, so 20 or so mums a year get a similar life-changing call like I did.

PKU is a metabolic disorder that prevents the normal breakdown of a protein found in most foods, which causes protein by-products to build up in the blood stream. This build-up prevents the brain from developing properly. Progressive intellectual disability results if PKU is not managed from early infancy.

The only way to manage PKU is through a strict, lifelong low protein diet and special formulas. For those with PKU, their diet is restricted to just 1-8 grams of protein a day, compared to 46-64 grams of protein a day for those without PKU. While we all know that meat, fish and eggs contain protein, there’s protein in everything from bread, fruit and vegetables, to even my own breast milk.

LISTEN: Mia Freedman spoke to Vanessa Cranfield about what it's like to parent a child with a disability on No Filter (post continues after audio...)

At the point of her diagnosis, I had to limit my breast feeding and Sophia’s main food source came from a special formula. At each feeding time, I had to first feed Sophia her required dosage of formula followed by topping her up with breast milk, which was a very hard and painful process.

It’s been determined that Sophia can have six grams of natural protein a day. That’s the equivalent of two slices of bread, or three bananas – no less, no more. Most of her food must come from a small range of special products for people living with PKU.

Making sure Sophia thrives like any other kid is a careful balancing act. To ensure Sophia grows as she should, she needs to take a supplement containing synthetic protein, three times a day. With this, a blood test is required every week, to let us know if she needs to increase or decrease her protein intake for the week.

Eight years on, Sophia is a bright, cheeky girl in grade three who loves music, drama and sport.

We have been quite lucky with Sophia, as she is strong and resilient. However, things have been getting tougher for her as she gets older and realises she cannot eat all the things we do.

Sophia now has a two-year-old brother, Michael, who does not have PKU. There have been a few tears at the dinner table when Sophia became very aware of the difference in her diet. We do our best to come up with similar alternatives but at the same time, we can’t change our diets fully, as this is something that Sophia is not going to grow out of.

In many ways, Sophia has embraced having PKU, but there are still many challenges. Nevertheless, I am so proud of our girl and her positive attitude towards PKU.

In honour of Sophia, and her strength, we are encouraging Aussies to participate in 'The Great Protein Challenge: How Low Pro Can You Go?', a great initiative being run by the Metabolic Dietary Disorders Association (MDDA). The challenge encourages people experience a typical day in the life of a person living with PKU by significantly reducing their protein intake for 24 hours.

To learn more about the initiative or to make a donation to support Australians with PKU, please visit www.thegreatproteinchallenge.com.au