Figure 1 (A) Pedigree of the family with hereditary neuropathy with liability to pressure palsies (HNPP) with the splice site mutation. Black symbols indicate affected individuals; circles, females; squares, males; roman numerals, generations; arabic numbers, individuals. (B) Transverse semithin section from the sural nerve biopsy of patient II.1. The density of myelinated fibres is normal. Several fibres show focal thickenings of the myelin sheath (arrows), typical of HNPP. Stain, toluidine blue; bar = 20 µm. (C) Agarose gel electrophoresis of polymerase chain reaction (PCR) products obtained from the amplification of the cDNAs from the patient II.1 (lanes 2 and 5) and from normal control (lanes 1 and 4). The 984 bp PCR product corresponds to the control gene G3PDH (glyceraldeyde‐3‐phosphate dehydrogenase). Lane 3: DNA molecular weight marker IX (φX174). Lane 6: DNA molecular weight marker XIII (Roche). (D) Schematic figure representing the structure of the PMP22 gene and the position of the primers used; PMP22‐RT F (→), PMP22‐intr2R (←) and PMP22‐RT R (grey reverse arrow). Grey line shows a possible mechanism of splicing of the transcript from the mutated allele.