Hi @choim09,
There are some SNOMED and MedDRA terms that can’t be mapped 1-to-1 where we need to implement uphill mapping. But, this is not the actual issue that prevents us from creating a single hierarchy between MedDRA and SNOMED. The actual issue is that when you build the hierarchy the semantics of each term implies not only the actual terms but also a subset of all its descendants. If the rules on which the descendants are gathered are different, then you need to consider all the concepts down the hierarchy when you deal with each concept. What is not a trivial task.
We will ping you in PM.