YOUNG people from Westbury and Corsham whose brothers or sisters suffer from the genetic condition Tuberous Sclerosis, travelled to the House of Commons.
The group visited Westminster to highlight the lack of support for sufferers of the condition.
They also want to lobby the government to provide DNA testing on the NHS, for families who have the gene, and want to know whether it has been passed down.
Katie Jones, 18, from Broadmead, Corsham, has a younger brother Nicholas, 13, who suffers from the disorder. He was diagnosed with the condition when he was only four weeks old.
Nicholas's mother Sue said: "A lot of people like Katie are very anxious, they want to know about their future. That's why it's such a big deal that these DNA tests are not on the NHS."
Last year, Katie and a friend decided to organise a group for brothers and sisters of TS-affected children.
The Siblings group was launched at Planet Hollywood, and since then has generated a great deal of interest.
The group has now created an interactive website offering young people a chance to share their experiences of living with someone with TS.
Joanne Brothers from Westbury has an 11-year-old daughter who suffers from TS.
Her other daughter, 13-year-old Kaylith, who does not have the disorder, also visited London on Thursday.
Her sister was diagnosed as having TS when she was five months old.
TS is an inherited disease. Patients are at risk of developing tumours in organs including the brain, kidneys and in some babies, the heart.
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