What Is HSAN-7?
HSAN-7 is a type of CMT caused by autosomal dominant mutations in the SCN11A gene. This gene provides instructions for making part of a sodium channel that regulates the excitability of pain-sensing nerve cells. Mutations in the SCN11A gene disrupt this function, leading to impaired nerve signal transmission.
HSAN-7 is autosomal dominant, meaning that just one of the gene’s two copies needs a mutation to cause this subtype.
Clinical Features
The age of symptom onset in HSAN-7 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-7 symptoms may include:
- Progressive loss of sensation in the feet and hands
- Loss of pain and temperature sensation
- Excessive sweating (hyperhidrosis)
- Gastrointestinal dysmotility (impaired movement through the digestive tract)
- 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-7 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.
