What Is HMSN-6C?
HMSN-6C is a type of CMT caused by autosomal recessive mutations in the PDXK gene. This gene provides instructions for making pyridoxal kinase, an enzyme that activates vitamin B6 into the form the body uses in many nerve cell processes. Mutations in the PDXK gene disrupt this function, leading to impaired nerve signal transmission.
HMSN-6C 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 HMSN-6C is variable, ranging from childhood to adulthood. Symptoms typically begin in the lower extremities and progress over time to involve the upper limbs. Nerve conduction studies usually show somewhat slowed conduction velocities and reduced amplitudes, consistent with an axonal form of CMT.
HMSN-6C symptoms may include:
- Weakness in the feet and lower legs
- Muscle atrophy
- Foot drop
- Reduced or absent reflexes
- Reduced sensation
- A steppage-style walking pattern
- Foot deformities, including high arches, and hammertoes (clawed toes)
- Progressive involvement of the hands and forearms
- Difficulty with fine motor skills and manual dexterity
- Additional symptoms not listed here
Disease Course
HMSN-6C 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.
