Purpose: An evidence-based approach was used to determine the frequency distribution of genes contributing to the Charcot-Marie-Tooth (CMT) disease phenotype. Methods: We performed a combined analysis of 11 populationbased studies from various ethnic backgrounds to generate an evidence-based testing scheme. To estimate the relative frequencies of the responsible genes for which population-based studies are not available, we used our cohort of clinically classified patients with CMT and related neuropathies collected before the availability of genetic testing. Results: Similar mutation frequencies were detected in the various studies, revealing a uniform distribution of pathogenic mutations. In CMT1 70% of patients harbor the CMT1A duplication, followed by GJB1 mutations at 8.8%. MPZ and PMP22 mutations are less common, identified on average in 2.9% and 1.5% of patients,respectively. Other genes not tested in population-based studies contribute to less than 1% of disease individually.In CMT2 MFN2 mutations are the most common, although population-based studies are not yet available.
Conclusion:CMT represents a heterogeneous group of disorders at the molecular level. Nevertheless, testing for the CMT1A duplication (i.e., duplication of PMP22) alone yields an accurate molecular diagnosis in approximately half of all patients. If one further specifies the clinical type (demyelinating vs. axonal), the yield of detecting a molecular defect increases to 75% to 80% in the demyelinating or CMT1 group with a screening test that evaluates for CMT1A duplication/hereditary neuropathy with liability to pressure palsies deletion and GJB1 point mutations. Case vignette: A 35-year-old man presents with a 5-year history of numbness in his feet and occasional tripping. Family history reveals that he has an 8-year-old daughter. He and his wife lost a 5-year-old daughter 1 year ago, who developed acute lymphoblastic leukemia and became paralyzed after the first dose of chemotherapy. His wife is expecting another child.
Genet MedSigns and symptoms of peripheral neuropathy are often identified during office visits to both the neurologist and generalist physician. When neuropathy presents in the context of a systemic illness, such as diabetes or uremia, the acquired nature is easily recognized. However, in the absence of overt systemic illness, the ability to distinguish acquired from inherited neuropathies on clinical grounds is often challenging, particularly in sporadic disease.Charcot-Marie-Tooth (CMT) and related peripheral neuropathies represent a heterogeneous group of hereditary disorders of the peripheral nervous system with an estimated frequency of 1 in 2500 individuals. 1 CMT is characterized by slow and progressive weakness of the legs followed, in some cases, by hand involvement. On the basis of motor nerve conduction velocities (NCVs), two major types can be distinguished: the demyelinating form (CMT1), which is characterized by symmetrically slowed NCV (usually Ͻ 38 m/sec; normal is Ͼ 45 m/sec), and the axonal form (CMT...