Genetic factors may be learnt from families with gene mutations that render nerve-injury sus-ceptibility even to ordinary physical activities. A typical example is hereditary neuropathy with liability to pressure palsies (HNPP). HNPP is caused by a heterozygous deletion of PMP22 gene. PMP22 deficiency disrupts myelin junctions (such as tight junction and adherens junctions), leading to abnormally increased myelin permeability that explains the nerve susceptibility to injury. This ifnding should motivate investigators to identify additional genetic factors contribut-ing to nerve vulnerability of injury.