Study Identifies Differences in Progression and Onset Between Type 4B1 and 4B2 Charcot-Marie-Tooth Disease

According to a story from Charcot-Marie-Tooth News, a recent study was conducted that compared the presentation of symptoms between two different variants of Charcot-Marie-Tooth disease (CMT): CMT4B1 and CMT4B2. The scientists found that type 4B1 was overall more severe compared to type 4B2, with earlier onset of symptoms, greater developmental delays, and more frequent respiratory complications. There are three different sub types of Charcot-Marie-Tooth disease type 4B in total.

About Charcot-Marie-Tooth Disease (CMT)

Charcot-Marie-Tooth disease is a hereditary disorder of the peripheral nervous system. It is most characterized by a progressive loss of touch sensation and muscle tissue in several different parts of the body. The cause of this disease is usually linked to a genetic mutation, but the mutation involved varies depending on the variant of Charcot-Marie-Tooth disease. There are multiple types of Charcot-Marie-Tooth disease, with all types aside from type 2 having a demyelinization effect. Type 2 causes damage to the neuronal axon instead. Symptoms include foot drop, muscle wasting (typically in the arms, legs, and hands), painful muscle spasms, loss of sensation in the limbs, scoliosis, trouble speaking, chewing, swallowing, and tremors. Treatment typically includes therapy and surgery in order to maintain function. There is no cure. The disease can occur early in life or as late as the 30s and 40s. To learn more about Charcot-Marie-Tooth disease, click here.

About The Study

The type 4B variants of the illness are among the most rare types. All three of the sub types have been determined to be clinically unique from each other. They are often characterized by early onset of symptoms, excessive focal formulation of myelin (the insulating fatty sheath that coats nerve cells and helps them function), and significantly slower nerve conduction. 

The study was conducted over a period spanning July 2016 until January 2019 and assessed a total of 50 patients. Of this group, 26 were diagnosed with 4B1, 19 of them had 4B2, and the remaining five had 4B3. The analysis revealed a clear disparity in average age of onset, which was 6.7 years for 4B2 but just 2.8 years for 4B1. Almost all patients with 4B1 experienced weakness of the lower limbs as their first symptom. Meanwhile, most 4B2 patients saw lower limb weakness, walking difficulties, or hand tremors. Congenital glaucoma was also present.

4B1 patients were far more likely to have motor milestone delays (50 percent vs 20 percent), but scoliosis was more common in 4B2 patients. Measures of muscle strength indicated substantially more severe muscle weakness in 4B1, and age had a stronger correlation with disease severity (the older the patient, the worse the symptoms). The researchers concluded that overall, Charcot-Marie-Tooth disease type 4B1 was more severe than type 4B2.

Check out the original study (from the journal Annals of Neurology) here.

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