What Is dSMA-5?
dSMA-5 is a type of CMT caused by autosomal recessive mutations in the DNAJB2 gene. This gene provides instructions for making a protein that helps clear damaged proteins from motor nerve cells. Mutations in the DNAJB2 gene disrupt this function, leading to impaired nerve signal transmission.
dSMA-5 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 dSMA-5 is variable, ranging from childhood to adulthood. As a motor neuropathy, dSMA-5 primarily affects the most distal points, with weakness and atrophy of the feet and hands, and little to no involvement of the sensory nerves. Nerve conduction studies usually show somewhat slowed conduction velocities and reduced amplitudes, consistent with an axonal form of CMT.
dSMA-5 symptoms may include:
- Weakness and atrophy in the feet and lower legs
- Foot drop
- Reduced or absent reflexes
- A steppage-style walking pattern
- Foot deformities, including high arches, and hammertoes (clawed toes)
- Progressive involvement of the hands
- Difficulty with fine motor skills and manual dexterity
- Additional symptoms not listed here
Disease Course
dSMA-5 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.
