MPs will hear evidence from those involved in a disagreement between NHS England the drugs firm Vertex Pharmaceuticals over the price of the drug Orkambi today (Thursday)
The treatment could transform the lives of thousands of people in the UK but there is no sign of an agreement being reached two years after negotiations started.
The Health and Social Care Committee (HSCC) is holding an evidence session in the hope of breaking the deadlock.
Among parents who have given evidence to the committee is Natasha McIntyre, of Morley, whose three-year-old daughter Amélie has the illness.
Mrs McIntyre said Orkambi would avoid the need for Amélie to take multiple drugs and have physiotherapy every day and would halt an expected decline in her lung function.
The family were told Amélie would be able to start taking the drug from the age of six.
Mrs McIntyre, 37, said: "When she was diagnosed the nurse said it was going to be OK because this new drug had been passed.
"Then all of a sudden you find out you can't have it. It's like my daughter's life is not worth it it for the Government or the NHS.
"It's a drug for my daughter but the effect it would have on my family would be incredible.
"She's being priced out of enjoying her childhood."
The NHS has offered £500m over five years for access to Orkambi and other cystic fibrosis drugs made by Vertex.
But that was rejected by Boston-based Vertex, which has secured deals with other countries for access to Orkambi.
The HSCC will hear from Professor Stephen Powis, national medical director of NHS England, Sir Andrew Dillon, chief executive of the National Institute of Health and Care Excellence (NICE), Dr Jeff Leiden, president of Vertex, and Stuart Arbuckle, executive vice president of Vertex.
Orkambi is available in other countries including Germany, Italy, Sweden and the US. Patients in Germany have had access to the drug since 2015.
The Cystic Fibrosis Trust has said an immediate resolution is needed and interim access to the drug must be secured for patients.
Nick Medhurst, head of policy and public affairs at the Cystic Fibrosis Trust, "Other countries around the world have found a way which gives us hope that a compromise can be found.
"Cystic fibrosis is a progressive disease and every exacerbation of ill-health is something that may have been avoided with treatment that is available."
Rebecca Hunt, vice president of international corporate affairs at Vertex Pharmaceuticals said: "Vertex welcomes the committee’s interest in access to cystic fibrosis medicines and we look forward to continuing to support its inquiry into this important issue."