I just joined the list, so I apologize if someone else answered your question already, and now I am starting a new thread on the same topic. We have recently also asked ourselves a very similar question, how to reference items to wikidata in the gene infobox that appears on human gene pages. The solution we came up with is creating a link to the references section that then links back to the reference on the wikidata page for that item. For example, on the wikipedia page for the gene Reelin (
https://en.wikipedia.org/wiki/Reelin) there is a section in the infobox for "Genetically Related Diseases". In this section, there is a superscript [1] that is displayed in the reference section and is a link to the property Genetically Related Diseases in wikidata. This link looks like this
https://www.wikidata.org/wiki/Q414043#P2293 where Q414043 is Reelin and P2293 is Genetically Related Diseases. In your case, the link would look like
https://www.wikidata.org/wiki/Q158840#P485. The text for the reference is
"Diseases that are genetically associated with RELN view/edit references on wikidata". I generated the <ref>{{cite web |url=...</ref> tag via lua code on lines 578-591 of
Module:Infobox_gene . I think you should be able do something similar for your example and link the references for P485 to that section of the wikidata page.