Harry Copeland has a disability that affects a tiny number of people on the planet.

Key points: Rebecca Copeland says her son was left off the NDIS register when the family moved to Tasmania

Rebecca Copeland says her son was left off the NDIS register when the family moved to Tasmania She told an NDIS inquiry the system is exhausting and wearing people down

She told an NDIS inquiry the system is exhausting and wearing people down A Hobart man says his son died before his wheelchair could be modified so he could use it

The nine-year-old has pontine tegmental cap dysplasia, an extremely rare neurological condition with no known cause or cure.

A scientific website estimates as few as 20 people have the condition.

Harry is non-verbal and has various other physical and intellectual disabilities, including difficulties seeing, hearing and swallowing.

His mother, Rebecca, said there used to be plenty of support to help him.

"We moved from Western Australia three years ago and we had access to great support, great health providers — you name it, we had it," she said.

"I didn't know how lucky I was when we were there."

While her son's condition is very rare, the family's struggles with the National Disability Insurance Scheme (NDIS) are not.

The Joint Standing Committee on the NDIS sitting in Hobart has heard myriad stories from frustrated and emotional parents.

"Our journey with the NDIS has not been fun. It's been stressful, it has been heartbreaking and it has been exhausting," she told the hearing.

"He was left off the register when NDIS first came to Tasmania so I sat waiting … I rang and rang and rang and they'd lost us, they didn't know who we were," Ms Copeland said.

"We've been through seven or eight planners because every time we get a planner, they resign because the conditions are so difficult for them to work in.

"Plans get half finished and then that planner leaves and no-one knows where the plan is or where it's up to … reports get lost, that's happened numerous times."

Rebecca Copeland and her husband with their children Oscar, 11, Harrison, 9 (in wheelchair), and Willow, 5. ( Supplied )

Ms Copeland said the system wore parents and carers down.

"The fact I've had to fight so hard and go down so many avenues to get the help he needs, it's exhausting for parents and carers. It shouldn't be so hard."

21yo died waiting for $400 wheelchair upgrade

Warren Lewis told the hearing about the plight his son faced before he succumbed to muscular dystrophy. ( ABC News: Annah Fromberg )

Warren Lewis told the hearing about his son, Jarrad, who had muscular dystrophy.

Jarrad died in June as a result of his condition.

He had been given an electric wheelchair in 2016, but it needed $400 worth of customisation to allow him to sit in it properly.

"Three years later he still wasn't able to use it and with his passing we had to return it," Mr Lewis said.

He explained Jarrad had been on the NDIS since the trial in 2013 and the processes to get support changed constantly.

"We went through 12 processes in six years and the process changed every year. Every year something was different," he said.

"I find it disturbing, distressing and upsetting."

Paperwork and phone calls 'beyond people'

Lisa Denny spend up to 16 hours a week on NDIS administration for her son, Rory. ( Supplied: Lisa Denny )

Demographer Lisa Denny told the inquiry she spent 12 to 16 hours a week on administration for her 10-year-old son Rory.

He has a genetic abnormality, but Ms Denny said it does not fully explain his level of disability, making his official diagnosis an "unexplained case".

"The administrative burden and the complexity of the planning processes and its multitude of policies and procedures is beyond many of the carers and recipients that it's supposed to be designed to benefit," she said.

"The system requires perseverance, time, understanding and more persistence to actually benefit from it."

"There's a lot of work that needs to be done. It's hard, it's emotional and you just keep going because you can't give up."

More than 6,000 Tasmanians are part of the NDIS.

The committee will report back to the Federal Government with recommendations at the end of the year.