Under fourth normal form, a record type should not contain two or more independent multi-valued facts about an entity. In addition, the record must satisfy third normal form. The main problem with violating fourth normal form is that it leads to uncertainties in the maintenance policies.
Fifth normal form deals with cases where information can be reconstructed from smaller pieces of information that can be maintained with less redundancy. Second, third, and fourth normal forms also serve this purpose, but fifth normal form generalizes to cases not covered by the others.
Fourth and fifth normal forms both deal with combinations of multivalued facts.