My youngest brother is 24 and has a genetic condition with moderate learning disabilities. He has never worked and gets UC LCRWA (I think that's what it's called, he has no work comittments). He is never going to work other than something that is designed for those with LDs and very part time. DM is thinking to start a SIPP for him, even just £100 pcm as she's concerned that there may not be any welfare benefits by then. Are there any possible downsides to this from a financial perspective?