Atypical hereditary neuropathy with liability to pressure palsies (HNPP): the value of direct DNA diagnosis.

We report two patients with suspected hereditary liability to pressure palsies. Neurophysiological studies showed a mixed axonal-demyelinating sensory-motor polyneuropathy with focal slowing of conduction velocities at the common sites of entrapment. Morphological studies on sural nerve biopsy from the proband showed active axonal regeneration without typical tomacula. Molecular analysis confirmed the presence of a deletion of chromosome 17p11.2 in both patients. Our observation confirms the heterogeneity of hereditary liability to pressure palsies and the relevance of DNA testing for the diagnosis of this hereditary neuropathy.