Overview of Charcot-Marie-Tooth Disease Type 1A

Area of Science:

• Genetics
• Neurology
• Molecular Biology

Background:

• Type 1A CMT disease is frequently associated with a segmental duplication on chromosome 17p11.2.
• This duplication results in an increased gene dosage of the peripheral myelin protein 22 (PMP22) gene.
• The disorder typically follows an autosomal dominant inheritance pattern.

Purpose of the Study:

• To investigate the genetic basis of Charcot-Marie-Tooth type 1A disease.
• To understand the relationship between PMP22 gene dosage and disease phenotype.
• To characterize the pathological mechanisms underlying CMT1A.

Main Methods:

• Analysis of nerve biopsies.
• Genetic analysis to identify duplications and point mutations in the PMP22 gene.
• Clinical phenotyping of affected individuals.

Main Results:

• Increased PMP22 gene dosage due to duplication is the primary cause of CMT1A.
• Symptom onset typically occurs in the first decade, with nerve conduction velocity slowing evident by age 2.
• Pathological findings include active demyelination in childhood, hypertrophic onion bulb changes, and progressive axonal loss.
• Common phenotypes include distal muscle wasting, weakness, and sensory loss; other variants involve tremor, ataxia, or severe sensory deficits.

Conclusions:

• Genetic duplication of PMP22 is the main driver of CMT1A.
• The disease mechanism involves developmental demyelination and subsequent axonal degeneration.
• Clinical presentation is variable, ranging from typical CMT to Roussy-Lévy syndrome.