Transgenic mouse models of CMT1A and HNPP.

We have generated several PMP22 animal mutants with altered PMP22 gene dosage. A moderate increase in the number of PMP22 genes led to hypomyelination comparable to CMT1A, whereas high copy numbers of transgenic PMP22 resulted in phenotypes resembling more severe forms of hereditary motor and sensory neuropathies. In contrast, eliminating one of the two normal PMP22 genes by gene targeting caused unstable focal hypermyelination (tomacula) similar to the pathology in HNPP. A related but more severe phenotype was observed in mice that lack PMP22 completely. Detailed analysis of the different PMP22 mutants revealed, in addition to the obvious myelinopathy, distal axonopathy as a characteristic feature. We conclude that the maintenance of axons might be a promising target for therapeutic interventions in these demyelinating hereditary neuropathies. Furthermore, our results strongly support the concept that PMP22-related neuropathies (and most likely also other forms of inherited motor and sensory neuropathies) should be viewed as the consequence of impaired neuron-Schwann cell interactions that are likely already to be operative during development. Such considerations should be taken into account in the design of potential novel treatment strategies.