The CDC now recommends a 4th vaccine dose to be given at least 12 weeks after the 3rd dose for mRNA vaccines in patients >12 years old with moderate or severe immunocompromise. No such recommendation is yet given by the CDC for <12-year-old individuals.
Given that APS1 patients carry type I IFN autoantibodies and many are also on immunomodulatory medications that can decrease immune function, and because of the higher risk of severe disease associated with the autoantibodies and their underlying autoimmune disease including pneumonitis, which affects up to 40% of all patients, I think it is reasonable to include APS1 in the moderately to severely immunocompromised category that CDC refers to. Therefore, a 4th mRNA vaccine dose in >12 year old patients, at least 12 weeks apart from the 3rd dose of vaccination is reasonable.