What Is HSAN-9?
HSAN-9 is a type of CMT caused by autosomal recessive mutations in the TECPR2 gene. This gene provides instructions for making a protein involved in autophagy, the process by which nerve cells clear and recycle their internal components. Mutations in the TECPR2 gene disrupt this function, leading to impaired nerve signal transmission.
HSAN-9 is autosomal recessive, meaning that both copies of the gene must have a mutation to cause this subtype.
Clinical Features
The age of symptom onset in HSAN-9 is variable, ranging from childhood to adulthood. The disease involves loss of sensation that begins in the hands and feet (glove-and-stocking distribution) and progresses over time towards the center of the body. Nerve conduction studies usually show somewhat slowed conduction velocities and reduced amplitudes, consistent with an axonal form of CMT.
HSAN-9 symptoms may include:
- Progressive loss of sensation in the feet and hands
- Loss of pain and temperature sensation
- Autonomic dysfunction
- Cognitive impairment and developmental delay
- Spasticity (muscle stiffness) and ataxia (impaired balance and coordination)
- Reduced or absent reflexes
- Foot deformities, including high arches, and hammertoes (clawed toes)
- Distal weakness that develops as the disease progresses
- Foot drop
- Additional symptoms not listed here
Disease Course
HSAN-9 shows wide variability in severity and progression. Some individuals are mildly affected, while others develop a more severe disease. Disease progression is generally slow, and life expectancy is not reduced.
