def METHOD_NAME(db_ns):
    """Return the prefix for the given INDRA namespace in Bioregistry."""
    # First if there is an explicit override, we return that
    if db_ns in bioregistry_overrides:
        return bioregistry_overrides[db_ns]
    # Next, if INDRA matches a curated synonym, we return that
    if db_ns in synonym_reverse:
        return synonym_reverse[db_ns]
    # Otherwise, we check if the lowercase version of the namespace if
    # a valid prefix and return that
    if db_ns.lower() in registry:
        return db_ns.lower()
    # If none of these match, we return None
    return None