The patient was tested for 2 of the most common causes of CMT: duplication of the PMP22  (peripheral myelin protein 22) gene (which accounts for approximately 67% of demyelinating CMT cases) and mutations in the MPZ (myelin protein zero) gene (approximately 10% of demyelinating CMT cases) (1).
2] Human genes: PMP22, peripheral myelin protein 22; MPZ, myelin protein zero; GJB1, gap junction protein, beta 1, 32kDa; MFN2, mitofusin 2.
If the family history is not consistent with male-to-male transmission, testing for PMP22  (peripheral myelin protein 22) gene duplication should be initially performed, because it is by far the most common type of CMT1 (CMT type 1) (approximately 70% of patients).
The three STRs were tested successfully in a family with one child carrying four copies of the PMP22 region and illustrating all possible allele combinations (Fig.
4] Nonstandard abbreviations: CMT, Charcot-Marie-Tooth; PMP22, peripheral myelin protein 22; RFLP, restriction fragment length polymorphism; STR, short tandem repeat; BAC, bacterial artificial chromosome; and HNPP, hereditary neuropathy with liability to pressure palsies.
4] Nonstandard abbreviations: CMT, Charcot-Marie-Tooth disease; CMT1A-REP, CMT1A repeat; PMP22
, peripheral myelin protein 22; HNPP, hereditary neuropathy with liability to pressure palsy; PFGE, pulsed-field gel electrophoresis; FISH, fluorescence in situ hybridization; STR, short tandem repeat; FAM, 6-carboxy-fluorescein; HEX, hexachloro-6-carboxyfluorescein; and TET, 4,7,2',7'-tetrachloro-6-carboxyfluorescein.
A 239-bp fragment including exon 3 and the intron-exon boundaries of the PMP22 gene was amplified using the primers described by Nicholson et al.
The 239-bp PMP22 fragment containing exon 3 and the exon-intron boundaries was amplified from DNA samples of two homozygous individuals (C/C and T/T) for the +31(C/T) polymorphism.
Two different unaffected genomic controls were also used: one homozygous +31 (T/T) for the intronic polymorphic site of PMP22 gene, which was coamplified with the competitive WTs, and other homozygous +31(C/C) for the polymorphic site, which was coamplified with the Ps.
2 was calculated by integration, and the target: reference PCR product ratio for both EW401 and PMP22 amplifications was calculated for each sample analyzed.
The average of both PMP22 and EW401 ratio results for CMT1A, unaffected, and HNPP samples were 1.
Each PCR amplification, EW401 with NF1 and PMP22 with NF1, was conducted in triplicate (on each of the 10 occasions) for each unaffected individual, and two averaged ratio values (EW401:NF1 and PMP22:NF1) were calculated.