Editor—Hereditary neuropathy with liability to pressure palsies (HNPP) or tomaculous neuropathy is an autosomal dominant disease.1 HNPP patients present with acute or recurrent transient muscle palsies and paraesthesias, usually after minor trauma. HNPP is characterised from the pathological point of view by the presence of sausage shaped swelling of the myelin sheath or tomacula2 in sensory and motor nerves.3

A deletion on the proximal short arm of chromosome 17 was detected in affected members of HNPP families.4 5 The deleted region is the same as that duplicated in Charcot-Marie-Tooth disease type 1 (CMT1A). While the CMT1A phenotype is mostly the result of extra dosage of the genes contained in this duplicated region, the HNPP phenotype results from monosomy of the same region in over 85% of cases.6 This duplication/deletion event is thought to occur because of the unequal crossing over between two large repeats bordering the CMT1A region,7 which encompasses 1.5 Mb of 17p11.2.8

The association between CMT1A and the peripheral myelin protein 22 (PMP22) gene, located within the CMT1A duplicated region, was established by the finding of point mutations …