What Is HSAN-1A?
HSAN-1A is a type of CMT caused by autosomal dominant mutations in the SPTLC1 gene. This gene provides instructions for making part of an enzyme involved in the production of sphingolipids, a class of fats essential to nerve cell membranes. Mutations in the SPTLC1 gene disrupt this function, leading to impaired nerve signal transmission.
HSAN-1A 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-1A is variable, typically in the second or third decade of life. The disease is sensory-predominant, with loss of pain and temperature sensation in the feet that leads to unnoticed injuries. Nerve conduction studies reflect a sensory and axonal process.
HSAN-1A symptoms may include:
- Progressive loss of sensation in the feet and lower legs
- Painless injuries and slow-healing foot ulcers
- Lancinating (shooting) pains in some individuals
- Reduced or absent reflexes
- Distal weakness that develops as the disease progresses
- Foot deformities
- Foot drop
- Additional symptoms not listed here
Disease Course
HSAN-1A 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.
