Two-year-old Millie Bea Hughes, from Rugeley, has to rely on a walking frame or an adult holding her up to get around.
Although Millie's illness means she can't properly play with brother Evan Ray, he has proved to be a dedicated companion – whether it's comforting her with her toy bunny when she's upset, sharing toys or fetching her shoes.
Their mother, Natalie Hughes, a 34-year-old detective constable with West Midlands Police, said it is 'really sad' that her two children cannot 'run off holding hands'.
She said: "Millie is such a character and is desperate to be able to get up and play with Evan.
"When you have twins you always imagine them to have a loving relationship and run off holding hands which you see with other people's twins — it's really sad that they can't do that."
Despite not being unable to run around together the pair share an incredibly close bond and little Evan, who's 13 minutes younger than Millie, always looks out for his sister.
Mrs Hughes added: "They love each other very much and he'll ask 'are you ok Millie?' and try and help her up.
"He fetches shoes and toys for her and always makes sure if he has a drink or biscuit she gets one too. When we go to the park he makes sure she has a good time and pushes her on the swing which is lovely to see."
Millie's parents, Natalie and power station engineer Chris Hughes, 34, are now trying to raise £40,000 so that Millie can have a non NHS-funded op called Selective Dorsal Rhizotomy, SDR.
The procedure involves cutting nerves in the lower spine that are responsible for muscle rigidity in a bid to improve mobility which would mean she may be able to walk, and run around playing with Evan.
The GoFundMe page, written as though Millie is talking, reads: "SDR means having an operation to make my legs work properly."
Speaking about the potential operation, Mrs Hughes said it would be 'brilliant' if her two children could play together.
She said: "Even at this age she knows she's dependent on us – if Evan goes off she wants to follow she announces 'me walk' and I hold her to follow after him. It would just be brilliant have them be able to play together."
Donations can be made to campaign.justgiving.com/charity/just4children/milliebeaswalkingwish