First Chinese Case of CMT4F Linked to Mutation in PRX Gene

A mutation in the periaxin (PRX) gene has been reported for the first time as the cause of Charcot-Marie-Tooth (CMT) type 4F in a Chinese patient.

The report, “Novel mutation in the periaxin gene causal to Charcot-Marie-Tooth disease type 4F” was published in the Journal of International Medical Research.

CMT4F is the result of mutations in the PRX gene that lead to movement and sensory impairment. The gene codes for a protein that plays an important role in maintaining the stability of myelin, the fat-rich substance that wraps around nerve fibers (axons). Mutations in the gene cause damage to the myelin sheath, which affects the function of peripheral nerves (those outside the brain and spinal cord).

To date, mutations in the PRX gene have been reported in dozens of patients throughout the world but none had been found in Chinese patients.

Now, a team of researchers has reported the first case of mutation in the PRX gene in a 14-year-old Chinese boy.

The boy, born from two healthy parents and with a healthy older sister, began walking when he was 1.5 years old. At this time, he showed clumsy walking and a tendency to fall. These symptoms progressed slowly, but by age 7, the muscles in his legs were weak to such an extent that he had difficulty standing up from a squatting position and was unable to pick up food with chopsticks.

“At the age of 14, he can still walk independently and feed himself with a spoon,” the researchers said.

During a neurological exam, clinicians noted he had scoliosis and pes cavus (high foot arch), a foot deformity associated with CMT, in both feet. Moreover, he showed severe muscle weakness.

Electrophysiological (the study of how electrical signals are transmitted through nerves in the body) analyses confirmed severe impairments to the function of peripheral nerves. The same analyses of both parents and his older sister detected no dysfunction at the motor and sensory nerves.

Clinicians suspected CMT and performed a genetic analysis for 39 CMT-related genes. They identified a mutation in exon 6 — the part of a gene with the information for protein production — of the PRX gene as the likely cause for the disease. The mutation identified has never before been reported.

“CMT patients with extremely low or undetectable sensory and motor nerve conduction and high levels of [cerebrospinal fluid] protein should be considered for PRX screening,” the authors wrote.

“To the best of our knowledge, this is the first patient of Chinese origin with a PRX mutation,” they concluded.