Mutational analysis of PMP22, EGR2, LITAF and NEFL in Greek Charcot–Marie–Tooth type 1 patients

To the Editor : Charcot–Marie–Tooth (CMT) disease is classified into CMT1 (demyelinating) and CMT2 (axonal) based on motor conduction velocities. Dominant CMT1 is the commonest in most populations, excepting communities with high consanguinity rates, where recessive CMT1 may be common (1). We recently reported on a cohort of Greek CMT1 patients screened for the PMP22 duplication and point mutations in GJB1 and MPZ . This screen elucidated the cause in ∼30% of cases, placing Greece among the countries with a low duplication frequency (2). To further elucidate the cause of CMT1 in the Greek population, we screened 86 undiagnosed patients from the original cohort for point mutations in PMP22 , EGR2 , LITAF and NEFL. Sixty-four cases were familial (50 suggestive of dominant inheritance) and 22 non-familial. Informed consent was obtained and DNA extracted from peripheral blood. Coding exons and adjacent intronic sequences of PMP22 , EGR2 , LITAF and NEFL were sequenced according to established protocols. Three pathogenic mutations were found (3.5%); two recently reported micromutations in PMP22 (3), and one known point mutation in EGR2 (4, 5). No pathogenic mutations were detected in LITAF or NEFL. All variants detected are shown in Table 1. Clinical and genetic details of patients with pathogenic mutations are shown in Table 2. The first PMP22 mutation was a de novo dominant 6 bp deletion in exon 4. The patient had severe CMT1 (Dejerine–Sottas phenotype). The second mutation was a dominantly inherited 21 bp duplication in exon 5. The patient had CMT1 and moderately restricted mobility throughout childhood. The mother carried the same mutation with a milder phenotype. The above mutations cause in-frame changes leading to stable transcripts and result in CMT1 of varying severity (3). The EGR2 mutation (Arg381His) was identified in an adolescent with severe CMT1 and no cranial neuropathies. It has been previously reported in patients with severe CMT1 and occasional cranial nerve involvement (4, 5). In one family, the proband developed cranial neuropathies in his 30s, but his affected daughter had none (4). In the other, the patient had congenital hypomyelination and Duane syndrome (5). It is too early to exclude a late emergence of cranial neuropathies in our patient. These cases show the phenotypic variability associated with the Arg381His mutation, most patients occupying the severe end of the CMT1 spectrum. The finding of two PMP22 (2.3%) and one EGR2 mutation (1.2%) in our cohort is in agreement with previously reported frequencies (1, 6). Given the rarity of mutations in LITAF and NEFL, it is no surprise that none were detected. Our data suggest that a molecular diagnosis can be reached in just over 35% of Greek patients with CMT1 (∼45% in cases suggestive of dominant inheritance) (2). This is considerably lower than most populations, such as the UK, where ∼60–80% of CMT1 patients are accounted for by the genes screened (6). Interestingly, studies from Turkey, Norway and Japan, all three relatively isolated populations, have yielded similar results to ours (2, 7). There is also some evidence that in the general population the PMP22 duplication frequency may be significantly lower than in clinic-based cohorts (7). Limitations in the methodology used to detect the CMT1A duplication and a somewhat permissive electrophysiological cut-off may have contributed to the low frequency observed in our cohort (2). Now that all genes known to cause dominant CMT1 have been screened and after excluding the CMT1A duplication with the most sensitive techniques, it would be important to screen familial cases consistent with recessive inheritance and isolated cases for known genes causing recessive CMT1. In general, recessive forms of CMT are rare in Europe, but in populations with increased consanguinity and in isolated populations this can be significantly higher (1). In addition, the presence of as yet unidentified genes contributing significantly to the pool of Greek CMT patients is a distinct possibility.