Molecular Diagnosis of PMP22 Duplication in Charcot-Marie-Tooth Patients by PCR-RFLP and MLPA Methods

Charcot-Marie-Tooth (CMT) is the commonest neurogenetic disorder with phenotypic and genotyping heterogeneity. CMT1A encompasses approximately 60% of all types of CMT and has AD inheritance. CMT1A maps to chromosome17 p11.2 and is majorly caused by 1.5 Mb DNA duplication that includes the peripheral protein 22 (PMP) genes. The severity, onset and progression of CMT1A vary markedly within and between families. Patients usually develop symptoms in the first two decades of life and onset after 30 years is rare. Patients develop a slowly progressive atrophy and weakness of the distal muscles of the leg and feet but rarely lose the ability to walk later in the disease course; most patients develop weakness and wasting in the hands. We investigated 67 patients compatible with electeroclinical presentations of CMT1A for the PMP22 gene duplication by PCR-RFLP method. Moreover, the RFLP dosage test is uninformative if the patient is homozygous and an alternative test is required. In this study, PMP22 duplication was found in 36% of our patients. However, up to 30% of the cases with a CMT1 phenotype who had a strand exchange event outside the hotspot region could have remained undetected by our method. Therefore, we used this method as a screening approach to detect patients with crossovers in the hotspot and then performed MLPA to identify the remaining 30% of the patients with crossovers outside the hotspot. Key Note: The problems of genetic diagnosis of CMT are: a) many genes are involved in the same phenotype b) many phenotypes are caused by the same gene. So, a battery of genetic diagnosis needs to clarify the cause of the disease such as MPZ, PMP22 and EGR2 by PCR-Sequencing method to diagnose the point mutations.