The specific study I was referencing looked at multiple outcomes, not just a condition by condition comparison which I think is important because I believe a lot of our modern issues have a similar environmental cause. I do think there is a predisposition within families for injury from certain environmental issues. I see it in my husband's family where him and his siblings have a few minor issues with auto-immunity or allergies while his parents have nothing, but his nieces and nephews are plagued by an obscene level of neurological and auto-immune issues including type 1 diabetes, sensory processing disorder, autism, selective eating disorder, selective mutism, food allergies, ADHD, Depression, Anxiety, Hypothyroidism. My brother is the same (he is adopted) his entire cohort of biological siblings as well as himself have multiple and severe auto-immune and neurological issues from fibromyalgia, rheumatoid arthritis, hashimoto's disease, graves, bipolar, depression, anxiety, schizophrenia but non of them share one diagnosis, their issues all manifested in a different way, but clearly there is something about the family that has made them susceptible to auto immunity and neurological issues.