Charcot-Marie-Tooth neuropathy type 1 (CMT1), the most common hereditary neurological disorder in humans, is characterized by clinical and genetic heterogeneity. It is caused mainly by a 1.5 Mb duplication in 17p11.2, but also by mutations in the myelin genes PMP22 (peripheral myelin protein 22), MPZ (myelin protein zero), Cx32 (connexin 32; also called GJB1), and EGR2 (early growth response 2). In this study, we have screened 172 index cases of Italian families in which there was at least one subject with a CMT1 diagnosis for the duplication on 17p11.2 and mutations in these genes. Among 170 informative unrelated patients, the overall duplication frequency was 57.6%. A difference could be observed between the duplication frequency in familial cases (71.6%) and that observed in non-familial cases (36.8%). Among the non-duplicated patients, 12 were mutated in Cx32, four in MPZ, two in PMP22, and none in the EGR2. In the non-duplicated cases, the overall point mutation frequency for these genes was 25.0%. We describe the mutations identified, and consider possible genotype-phenotype correlation.

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Charcot-Marie-Tooth disease type 1 (CMT1) is the most common form of the hereditary motor sensory neuropathies (HMSN) with a prevalence in the Italian population of 9.4/ 100,000 inhabitants. CMT 1 is a genetically heterogeneous disorder. Forty CMT 1 families (35 with recurrence of cases and 5 sporadic cases) living in northeastern Italy were analyzed with the probe pVAW409R3 to reveal the presence of 17p11.2 duplication. The duplication frequency that resulted was about 82% and not significantly different in familial and in sporadic cases (p = 0.801). This kind of molecular analysis can be very useful for the differential diagnosis of CMT 1 and for the early diagnosis in the absence of a clear clinical manifestation.

The incidence rates of Duchenne and Becker muscular dystrophies (X-linked recessive) in a given sample of the Italian population were recalculated using the results of DNA and dystrophin analysis. While the incidence rate of Duchenne muscular dystrophy remained unchanged, the new figure for the incidence of Becker muscular dystrophy (7.2 per 100,000 male live births) was much higher than previously reported, since molecular diagnosis revealed additional cryptic cases, but this incidence is still an underestimate.

Charcot-Marie-Tooth disease type 1 (CMT1) is a peripheral neuropathy characterised by progressive distal muscular atrophy and sensory loss with markedly decreased nerve conduction velocity, mostly inherited as an autosomal dominant trait. The most common form, type IA, is associated with a 1-5Mb DNA duplication in region pll.2-p12 of chromosome 17 in many patients.In this study a non-radioactive test for detection ofthe CMT1A duplication based on an RM11-GT microsatellite polymorphism is presented. Although different methods have been devised for this purpose, the present method has the advantage of being rapid, informative, economical, easily interpretable, and, therefore, it represents a very useful tool for diagnosis of CMT1A, especially before clear manifestation of clinical symptoms.Seventy-eight patients diagnosed clinically as having CMT and evaluated by electrophysiological methods were tested with an RMII-GT microsatellite and with probe pVAW409R3. The CMT1A duplication was found in 76% of the 56 unrelated patients. RMII-GT was the most informative marker with a heterozygosity of 89%.