[Molecular genetics of inherited neuropathies]

To clarify the specific features and molecular mechanisms of five diseases that we previously reported, we reviewed recent progress in HMSN-P linked to chromosome 3, CMT4F caused by PRX, CMT4A caused by GDAP1, CMT4B2 caused by SBF2/MTMR13F, and SCAN1 caused by TDP1. HMSN-P is characterized by late onset, proximal dominant severe muscle weakness, fasciculations, muscle cramp and sensory involvement. HMSN-P is a primary neuronopathy. Mutations in periaxin are associated with a broad spectrum of demyelinating neuropathies including DSS, a sensory dominant form and early onset slowly progressive CMT. Pathologically, loss of myelinated fibers, demyelination, small onion bulb formations, tomacula formation and myelin foldings were seen in sural nerves. Absence of septate like junction in the paranodal loop suggests that periaxin could be required for the adhesion complex. GDAP1 is a relatively common cause of CMT4. Half of reported patients showed the demyelinating form, while the rest showed the axonal form. The typical feature of CMT4A is paresis of the vocal cords and diaphragm. CMT4B2 is characterized by autosomal recessive, juvenile onset glaucoma and focally folded myelin in sural nerves. SBF2/MTMR13 mutations cause CMT4B2. Early onset glaucoma was seen in patients with nonsense mutations. SBF2/MTMR13 and MTMR2, which is the cause of CMT4B1, could be acting on the same 3-phosphoinositide signaling pathway. Clinical phenotypes of patients with SCAN1 showed cerebellar ataxia and axonal neuropathy. TDP1 acts on the single strand break repair pathway, and works specifically on topoisomerase I related SSBR. Disruption of TDP1 could induce a delay in the transcription process. The low rate of protein supply could lead to deaths of large neuronal cell.