Rapid genetic screening of Charcot-Marie-Tooth disease type 1A and hereditary neuropathy with liability to pressure palsies patients

Abstract

We used the allele-specific PCR-double digestion method on peripheral myelin protein 22 (PMP22) to determine duplication and deletion mutations in the proband and family members of one family with Charcot-Marie-Tooth disease type 1 and one family with hereditary neuropathy with liability to pressure palsies. The proband and one subclinical family member from the Charcot-Marie-Tooth disease type 1 family had a PMP22 gene duplication; one patient from the hereditary neuropathy with liability to pressure palsies family had a PMP22 gene deletion. Electron microscopic analysis of ultrathin sections of the superficial peroneal nerve from the two probands demonstrated demyelination and myelin sheath hyperplasia, as well as an 'onion-like' structure in the Charcot-Marie-Tooth disease type 1A patient. We observed an irregular thickened myelin sheath and 'mouse-nibbled'-like changes in the patient with hereditary neuropathy with liability to pressure palsies. In the Charcot-Marie-Tooth disease type 1A patient, nerve electrophysiological examination revealed moderate-to-severe reductions in the motor and sensory conduction velocities of the bilateral median nerve, ulnar nerve, tibial nerve, and sural nerve. Moreover, the compound muscle action potential amplitude was decreased. In the patient with hereditary neuropathy with liability to pressure palsies, the nerve conduction velocity of the bilateral tibial nerve and sural nerve was moderately reduced, and the nerve conduction velocity of the median nerve and ulnar nerve of both upper extremities was slightly reduced.

Keywords: Charcot-Marie-Tooth disease; PCR-double digestion method; action potential; gene mutation; hereditary neuropathy with liability to pressure palsies; myelin sheath; neural regeneration; neuropathology; peripheral myelin protein 22.

Figure 1

Family pedigrees. (A) CMT1A family; (B) HNPP family. ↗: Proband; ▪: male patient; ●: female patient; □: normal male; ○: normal female; : deceased male; ∅: deceased female. CMT1: Charcot-Marie-Tooth disease myelin sheath type; HNPP: hereditary neuropathy with liability to pressure palsies.

Figure 2

Ultrastructural nerve pathology (transmission electron microscopy, × 5 000) in CMT1A and HNPP. (A) CMT1A: Superficial peroneal nerve pathology indicated by irregular thickening of the myelin sheath of myelinated nerve fibers, onion-like structures (→), and enlarged gaps in the myelin sheath surrounding the axons (↓). (B) HNPP: Superficial peroneal nerve pathology indicated by a degenerated myelin sheath of myelinated nerve fibers, irregular thickening, loosing, edema, and a ‘mouse-nibbled’ appearance (←). CMT1: Charcot-Marie-Tooth disease myelin sheath type; HNPP: hereditary neuropathy with liability to pressure palsies.

Figure 3

Electropherograms showing PCR and double digestion of the PMP22 allele. (A, B) PCR amplification products with the indicated primer pairs. 1: A-III1; 2: A-II3; 3: A-II4; 4: B-II3; 5: B-II4; 6: B-III1; 7: normal control; 8: CMT1A positive control. (C, D) PCR amplification products with the indicated primer pairs (the first three lanes of each half) and EcoRI and NsiI double digestion of the PCR products (the second three lanes of each half). 1: A-III1; 2: B-II3; 3: normal control; M: DNA marker. CMT1: Charcot-Marie-Tooth disease myelin sheath type; PMP22: peripheral myelin protein 22.