What Is the Difference Between CMT Type 1 and Type 2?

If you have been diagnosed with Charcot-Marie-Tooth (CMT) disease, you likely want to understand exactly what is happening in your body. The most common question patients ask is about the difference between CMT Type 1 (CMT1) and CMT Type 2 (CMT2). At its core, the difference comes down to which part of the nerve is primarily damaged ^[1].

To understand this, it helps to think of your nerves as electrical wires carrying signals from your brain to your muscles. A standard electrical wire has two main parts: an inner copper core that carries the electricity, and an outer plastic insulation that protects the core and helps the signal travel quickly. Your nerves are built the exact same way. The inner core is called the axon, and the outer insulation is called the myelin sheath.

CMT Type 1: Damage to the Insulation

CMT Type 1 is often called a demyelinating neuropathy ^[1][2]. This means the genetic mutation primarily damages the protective insulation (the myelin sheath) surrounding the nerve ^[3][4].

When the myelin insulation is damaged or degrades, the nerve signal is forced to travel much slower than normal ^[1]. If your doctor performed a nerve conduction study (NCS)—a test where mild electrical pulses are used to measure nerve function—they likely noted that your nerve conduction velocity (NCV) was significantly slowed down ^[2][5]. Generally, speeds below 38 meters per second in the arm nerves point toward CMT1 ^[6].

While the signal still reaches the muscle, the delay makes it harder for the brain to coordinate movements quickly and efficiently. Over time, the poor insulation can eventually lead to secondary damage of the inner wire (the axon) as well ^[7][8].

CMT Type 2: Damage to the Wire Core

CMT Type 2 is known as an axonal neuropathy ^[1][2]. In this type, the protective insulation is relatively healthy, but the inner wire core itself (the axon) is damaged or degenerating ^[9][10].

Because the insulation is mostly intact, the nerve signals that do get through travel at a normal or near-normal speed (typically above 38 meters per second) ^[10][6]. However, because the core wire is damaged, the strength or amount of the electrical signal that reaches the muscle is significantly reduced ^[10][11]. On your medical reports, this reduced signal strength is often referred to as a low amplitude ^[10][6].

Going back to the wire analogy, it is like trying to power a large appliance with a very thin, frayed wire; the electricity moves fast, but there simply isn’t enough power reaching the destination to do the job properly.

Quick Comparison

Why the Distinction Matters

While CMT1 and CMT2 affect the nerve differently, they both result in similar physical challenges, such as muscle weakness, foot drop, and sensory loss in the hands and feet. Fortunately, tools like physical therapy, targeted exercises, and orthotics (such as ankle-foot braces or AFOs) can effectively help manage these symptoms regardless of your type. The distinction between Type 1 and Type 2 is crucial for a few reasons:

• Diagnostic clarity: Doctors use the differences in nerve conduction speeds and signal amplitude to help pinpoint exactly which genetic mutation you might have ^[12][5]. (Note: NCS measures these nerve signals, whereas an EMG uses small needles to look at the muscle health directly).
• Disease progression: Both types generally progress slowly over many years, but different subtypes have different typical timelines ^[13][14]. For instance, CMT1A symptoms often progress consistently starting in childhood and adolescence, whereas many forms of CMT2 often do not appear or progress until adulthood ^[14].
• Future treatments: Because the biological root causes are different, future targeted therapies and gene therapies will likely be specific to whether the disease is demyelinating (CMT1) or axonal (CMT2) ^[15][16].

In some cases, patients may have features of both slow speeds and low amplitudes, which is sometimes referred to as Intermediate CMT ^[6][17]. Knowing your specific type empowers you to understand your symptoms, anticipate your needs, and participate actively in discussions about your care.