One of the major interests in recent years was the question for the role of JCV genotypes and TCR subtypes in the pathogenesis of JCV associated disease.  Although a large number of studies was published in recent years and the knowledge on sequence, structure and distribution of the JCV variants increased considerably, a functional association of specific types to virulence could not be found.  At present, the role of the widely distributed prominent rearrangements in the TCR remains unclear.  Similarly, the genotypes could be related to historical migrations in population studies suggesting a stable configuration of mutations.  However, individual genotypes were only seldomly linked to pathogenesis.